Dear Guys,   Please check the picture attached to view how i measure focal lenght with the help of sunlight..Please also check attached pictures of Sun at focal point .. i  have used a Wooden sheet & mount a empty bucket of Paint at the base to hold Mirror in place.A 2x2 square ordinary mirror piece is used as diagonal at 45 Degrees to get Sun image on a White Paper.The Sun image is about Half inch in size . The question is am i doing Right??? If i am getting Sun image in half inch size at about 55 inch focal lenght Does this mean that i am somewhere between  f 9 & f10. & my mirror is somehow spherical..   Any Suggestion/Correction is Strongly Appreciated.   Regards,

I would 2nd that comment. The primary correction needs to be held within +_
0.01% correction and that's usually with a primary that's F/4 or faster.
Also the RC of both the primary and secondary have to be close to the design
values, especially if you have little room for error in the final back focus
position.  In short, a DK is the easiest cass. to make but the level of
difficulty is certainly much higher then a Newtonian, especially if the
Newtonian is of moderate focal ratio and RC only needs to be in the
ballpark. If you're not confident of being able to hold the tolerances
you'll be much better off with a Newtonian and barlow.

Tony
BigEye Optics


----- Original Message -----
From: "a.johnw" <a.johnw@...>
To: <atm_free@yahoogroups.com>
Sent: Wednesday, December 31, 2008 9:09 AM
Subject: [atm_free] Re: ATM Cassegrain?


Comments about the ease of making a dk often don't point out that the
radius of curvature of the 2ndry  needs to be very closely matched to
the figure of the primary. The only truly easy thing about them is the
lack of the need for a complicated 2ndry mirror test. The primary can
also be null figured if reqd. Some would advise making the 2ndry 1st
and then a primary to match/

John

--- In atm_free@yahoogroups.com, lance clarke <alaskawolfjoe@...> wrote:
>
> The DK is easier to make both optically and mechanically. For the
secondary, you just make the secondary tool into a spherical test
plate (foucault null test this), and then use it to fringe test the
secondary mirror. As for figuring the primary of a DK, the elipsoid
is actually easier to figure than a parabola, or at least that was my
experience.
>
> Lance
>
>
>
>
> ________________________________
> From: albireo13 <albireo13@...>
> To: atm_free@yahoogroups.com
> Sent: Thursday, December 4, 2008 1:31:55 PM
> Subject: [atm_free] Re: ATM Cassegrain?
>
>
> Hmmm ... I'd like to play around with a SW simulator to check
> sensitivity of a design to variations in tilt and separation.
> I'm not a precision machinest so the mechanical construction issues
> may drive me to favor one design over another.
>
> Can anyone suggest a sw program for simulating Cass. optical
> systems? Something relatively basic, with spot diagram output would
> be nice. So far I've been using CassDes by Mike Jones. It comes
> up with designs and generates spot diagrams ... quite nice.
> However, it doesn't let you modify spacings, etc to test effects on
> the focal plane spot diagram.
>
> Rob
>
> --- In atm_free@yahoogroup s.com, "albireo13" <albireo13@ ..> wrote:
> >
> > I guess it boils down between which is harder to make
> successfully .... the ellipsoidal DK
> > primary or the hyperbolopidal CC secondary.
> >
> > If I go DK, what techniques have folks used for testing the DK
> primary?
> >
> > Thanks,
> > Rob
> >
> > Rob--- In atm_free@yahoogroup s.com, "Tony Gondola" <acgna@> wrote:
> > >
> > > In that case it really sounds like a longer focus DK would be
> the best
> > > balance between performance and ease of construction.
> > >
> > > Tony
> > >
> > > ----- Original Message -----
> > > From: "albireo13" <albireo13@>
> > > To: <atm_free@yahoogroup s.com>
> > > Sent: Wednesday, December 03, 2008 4:11 PM
> > > Subject: [atm_free] Re: ATM Cassegrain?
> > >
> > >
> > > > This would strictly be for visual ....
> lunar/planetary/ doubles.
> > > > With bigger CO and longer tube, I don't think Gregorian is
> worth it. I
> > > > won't use it for
> > > > terrestrial so a non-inverted view is not important.
> > > > Hmmm ....
> > > >
> > > > Rob
> > > >
> > > >
> > > > --- In atm_free@yahoogroup s.com, "Tony Gondola" <acgna@> wrote:
> > > >>
> > > >> Hi Rob,
> > > >>
> > > >> Since you're looking at a fairly long focal ratio system
> (F/15-18) I
> > > >> wouldn't think that the extended field performance
> performance would
> > > >> really
> > > >> be an issue. Also, keep in mind that a DK primary is simply an
> > > >> under-corrected Newtonian primary. As you go from a sphere to
> a parabolic
> > > >> surface you pass through the shape and correction required
> for the DK.
> > > >> It's
> > > >> usually around a conic constant of -0.8 or 80% of the full
> correction
> > > >> you'd
> > > >> usually apply for a Newtonian primary. You just have to know
> when to
> > > >> stop.
> > > >> Just plug in the correct target conic constant into your test
> data
> > > >> reduction
> > > >> software and you're good to go.
> > > >>
> > > >> To answer your question about Gregorian verses DK I ray
> traced two
> > > >> systems,
> > > >> both 6" F/16. The DK gives a diffraction limited FOV of
> 2.4' , the
> > > >> Gregorian
> > > >> gives 24'. Both systems were calculated with F 3.3 primaries.
> At first
> > > >> the
> > > >> Gregorian field looks great but it comes at the expense of a
> much larger
> > > >> diameter secondary. Interestingly, it's diffraction limited
> field
> > > >> performance is slightly better then an equivalent classical
> cassegrain
> > > >> but
> > > >> you'll pay for that obstruction percentage. I haven't played
> with that
> > > >> design enough to know how much that can be reduced but I
> suspect that
> > > >> because of the position of the secondary which is outside
> focus, it will
> > > >> always be larger then the other designs for an equal amount
> of field
> > > >> illumination.
> > > >>
> > > >> I think what this really comes down to is what is the scope
> going to be
> > > >> used
> > > >> for? If it's lunar and planetary viewing and imaging you may
> as well go
> > > >> with
> > > >> the DK and extend the f ratio out into the F/22-24 range.That
> will give
> > > >> you
> > > >> enough EFL that you won't need a barlow and the secondary can
> be kept
> > > >> small
> > > >> (sort of the whole point of a long focus cass.) At that F
> ratio, the
> > > >> diffraction limited field opens up to almost 4' (plenty for
> the intended
> > > >> use) and the image scale is just about perfect in terms of
> over-sampling
> > > >> for
> > > >> diffraction limited imaging without a barlow.
> > > >>
> > > >> Tony
> > > >>
> > > >>
> > > >>
> > > >>
> > > >>
> > > >> ----- Original Message -----
> > > >> From: "albireo13" <albireo13@>
> > > >> To: <atm_free@yahoogroup s.com>
> > > >> Sent: Tuesday, December 02, 2008 5:37 PM
> > > >> Subject: [atm_free] Re: ATM Cassegrain?
> > > >>
> > > >>
> > > >> > Hi Tony,
> > > >> > I was leaning towards a classical Cass for two reasons:
> > > >> >
> > > >> > 1. it has far better coma performance than a like-f-ratio
> DK
> > > >> >
> > > >> > 2. the primary is a paraboloid. I've done a few newt
> mirrors so doing
> > > >> > a
> > > >> > paraboloid is
> > > >> > something I understand. Doing an ellipsoid (DK) would be a
> leap of
> > > >> > faith
> > > >> >
> > > >> > Of course the hyperboloid secondary would be the CC
> challenge.
> > > >> >
> > > >> > I was always intruiged by a gregorian so that would be a
> neat option
> > > >> > too.
> > > >> >
> > > >> > Any thoughts on how a Greg. would compare to a DK under the
> stars?
> > > >> >
> > > >> > Rob
> > > >> >
> > > >> >
> > > >> > --- In atm_free@yahoogroup s.com, "Tony Gondola" <acgna@>
> wrote:
> > > >> >>
> > > >> >> I make 10" and 12.5" F/24 DK cassegrains on a regular
> basis. It would
> > > >> >> be
> > > >> >> by
> > > >> >> far the easiest cassegrain type to make. As you know the
> secondary is
> > > >> >> spherical and can be easily tested just just polishing out
> the tool
> > > >> >> and
> > > >> >> using that as a test plate. The primary is a bit easier
> then a good
> > > >> >> newtonian primary except that you really have to nail the
> overall
> > > >> >> correction
> > > >> >> if you want the best system performance.
> > > >> >>
> > > >> >> If tube length isn't a problem you might also consider a
> gregorian. It
> > > >> >> also
> > > >> >> uses a parabolic primary and slightly corrected secondary
> which is
> > > >> >> concave
> > > >> >> so it's also very easy to make and test.
> > > >> >>
> > > >> >> Tony
> > > >> >> BigEye Optics
> > > >> >>
> > > >> >>
> > > >> >>
> > > >> >> ----- Original Message -----
> > > >> >> From: "albireo13" <albireo13@>
> > > >> >> To: <atm_free@yahoogroup s.com>
> > > >> >> Sent: Tuesday, December 02, 2008 8:41 AM
> > > >> >> Subject: [atm_free] ATM Cassegrain?
> > > >> >>
> > > >> >>
> > > >> >> >I have always had the itch to do a ATM Cassegrain ..
> either Dall-
> > > >> >> > Kirkham or Classical Cassegrain. I've done a few
> Newtonian mirrors
> > > >> >> > so I
> > > >> >> > can handle paraboloids. The fastest I've done is a
> f/4.7. This is
> > > >> >> > a
> > > >> >> > modest size scope for visual use only, maybe 6-8"
> aperture and
> > > >> >> > f/15-18.
> > > >> >> >
> > > >> >> > Any thoughts on which would be easier to complete? Any
> hidden
> > > >> >> > pitfalls? I'd love to hear from others who have
> caompleted one.
> > > >> >> >
> > > >> >> >
> > > >> >> > Thanks,
> > > >> >> > Rob
> > > >> >> >
> > > >> >> >
> > > >> >> >
> > > >> >> > ------------ --------- --------- ------
> > > >> >> >
> > > >> >> > Yahoo! Groups Links
> > > >> >> >
> > > >> >> >
> > > >> >> >
> > > >> >>
> > > >> >>
> > > >> >> ------------ --------- --------- --------- ---------
--------- -
> --
> > ---
> > > > ---
> > > >> > ------------ -
> > > >> >>
> > > >> >>
> > > >> >>
> > > >> >> No virus found in this incoming message.
> > > >> >> Checked by AVG - http://www.avg. com
> > > >> >> Version: 8.0.176 / Virus Database: 270.9.12/1824 - Release
> Date:
> > > >> >> 12/2/2008
> > > >> >> 9:31 AM
> > > >> >>
> > > >> >
> > > >> >
> > > >> >
> > > >> >
> > > >> > ------------ --------- --------- ------
> > > >> >
> > > >> > Yahoo! Groups Links
> > > >> >
> > > >> >
> > > >> >
> > > >>
> > > >>
> > > >> ------------ --------- --------- --------- --------- --------- -
> --
> > ---
> > > > ------------ -
> > > >>
> > > >>
> > > >>
> > > >> No virus found in this incoming message.
> > > >> Checked by AVG - http://www.avg. com
> > > >> Version: 8.0.176 / Virus Database: 270.9.13/1825 - Release
> Date:
> > > >> 12/2/2008
> > > >> 8:44 PM
> > > >>
> > > >
> > > >
> > > >
> > > >
> > > > ------------ --------- --------- ------
> > > >
> > > > Yahoo! Groups Links
> > > >
> > > >
> > > >
> > >
> > >
> > > ------------ --------- --------- --------- --------- --------- -
> --
> > ------------ -
> > >
> > >
> > >
> > > No virus found in this incoming message.
> > > Checked by AVG - http://www.avg. com
> > > Version: 8.0.176 / Virus Database: 270.9.13/1827 - Release Date:
> 12/3/2008
> > > 5:41 PM
> > >
> >
>



------------------------------------

Yahoo! Groups Links





--------------------------------------------------------------------------------



No virus found in this incoming message.
Checked by AVG - http://www.avg.com
Version: 8.0.176 / Virus Database: 270.10.1/1870 - Release Date: 12/31/2008
8:44 AM

what the purpose of your mesument

 

verify

calculus

 

atm project

 

what kind of pecision do you need

 

 

jack 47'n 71'W

 

Dear Guys,   Please check the picture attached to view how i measure focal lenght with the help of sunlight..Please also check attached pictures of Sun at focal point .. i  have used a Wooden sheet & mount a empty bucket of Paint at the base to hold Mirror in place.A 2x2 square ordinary mirror piece is used as diagonal at 45 Degrees to get Sun image on a White Paper.The Sun image is about Half inch in size . The question is am i doing Right??? If i am getting Sun image in half inch size at about 55 inch focal lenght Does this mean that i am somewhere between  f 9 & f10. & my mirror is somehow spherical..   Any Suggestion/Correction is Strongly Appreciated.   Regards,

I give a pressure gage to my dauther for his car and byke

but his byke is a roud type whit 115 to 130 lb
not 30 like a car the gage go from 0 to 60

how i can divide the pressure simple way

just help

jack 47'n 71'W

Bonjour Jaques,

Sorry, but that's about as far as I go en francais!  Here's a link to
an ebay 'buy it now' auction a bike tire gage that reads up to 160
PSI, 11 bar.

<http://cgi.ebay.com/ZEFAL-TWIN-GRAPH-BIKE-AIR-TIRE-PRESSURE-GAUGE-TOOL-NEW_W0QQ\
itemZ380088082687QQcmdZViewItemQQptZCycling_Parts_Accessories?_trksid=p3286.m20.\
l1116>

It's a little expensive, at $US 19.99.  There may be some cheaper,
it's just the first that I saw that would go so high.

But it's a lot less trouble than building some rig that she would have
to hold between the pressure gage and the tire.

Knowing women as I do, which is hardly any at all, I'm sure that your
daughter appreciate it, too.

-Jim-

--- In atm_free@yahoogroups.com, "Jacques Savard" <jacquessavard@...>
wrote:
>
> I give a pressure gage to my dauther for his car and byke
>
> but his byke is a roud type whit 115 to 130 lb
> not 30 like a car the gage go from 0 to 60
>
> how i can divide the pressure simple way
>
> just help
>
> jack 47'n 71'W
>

Its also worth going here
http://networkadvertising.org/managing/opt_out.asp
to opt out of a variety of advertising systems but check tribal fusion
as you may have to visit their web site to opt out here.
http://www.exponential.com/who-we-are/privacy-policy.jsp
of course if you are really worried just set your browser to not accept
cookies but then a lot of sites wont work.

--


Si Hoc Legere Scis Nimium Eruditionis Habes

sorry, sent this to the wrong address

--


Si Hoc Legere Scis Nimium Eruditionis Habes

Hi Lance. I did sort of intimate that. There is still the problem of
having to make a mirror with a very specific curve which ever one is
made 1st. There was a uk home site that went into the problem in some
detail but it seems to have disappeared. It also intimated that higher
mag dk's suffered less extra coma.
I uploaded a cas spread sheet last year and had hoped to update it to
include dk figures but other things have been pressing. My search was
for a dual purpose instrument - moon fills the view at the cass end
and moderate wide field at the other end. What I hoped to do
eventually is come up with a simple corrector to allow a dk primary to
be used as an effective newt. Having said that though I still have
doubts about figuring the main mirror to match a known spherical
2ndry. It might be easier to use 2 conics and figure the 2ndry against
an artificial star. From memory texereau and others give information
on the modified mirror spacings needed to do that. One of the
attractions of going that way is that it would allow the use of a
commercial coma reducer at the newtonian end. Errors in the conic
constants will just alter the magnification. DK's aren't so simple.

John

--- In atm_free@yahoogroups.com, lance clarke <alaskawolfjoe@...> wrote:
>
> It is only difficult if you try to match the ROC of the secondary to
the figure of the primary.  It is much easier to finish the secondary,
and then figure the primary to match.
>
> Lance
>
>
>
> ________________________________
> From: a.johnw <a.johnw@...>
> To: atm_free@...
> Sent: Wednesday, December 31, 2008 12:09:10 PM
> Subject: [atm_free] Re: ATM Cassegrain?
>
>
> Comments about the ease of making a dk often don't point out that the
> radius of curvature of the 2ndry needs to be very closely matched to
> the figure of the primary. The only truly easy thing about them is the
> lack of the need for a complicated 2ndry mirror test. The primary can
> also be null figured if reqd. Some would advise making the 2ndry 1st
> and then a primary to match/
>
> John
>
> --- In atm_free@yahoogroup s.com, lance clarke <alaskawolfjoe@ ...>
wrote:
> >
> > The DK is easier to make both optically and mechanically.  For the
> secondary, you just make the secondary tool into a spherical test
> plate (foucault null test this), and then use it to fringe test the
> secondary mirror.  As for figuring the primary of a DK, the elipsoid
> is actually easier to figure than a parabola, or at least that was my
> experience.
> >
> > Lance
> >
> >
> >
> >
> > ____________ _________ _________ __
> > From: albireo13 <albireo13@ ..>
> > To: atm_free@yahoogroup s.com
> > Sent: Thursday, December 4, 2008 1:31:55 PM
> > Subject: [atm_free] Re: ATM Cassegrain?
> >
> >
> > Hmmm ... I'd like to play around with a SW simulator to check
> > sensitivity of a design to variations in tilt and separation.
> > I'm not a precision machinest so the mechanical construction issues
> > may drive me to favor one design over another.
> >
> > Can anyone suggest a sw program for simulating Cass. optical
> > systems? Something relatively basic, with spot diagram output would
> > be nice. So far I've been using CassDes by Mike Jones. It comes
> > up with designs and generates spot diagrams .... quite nice.
> > However, it doesn't let you modify spacings, etc to test effects on
> > the focal plane spot diagram.
> >
> > Rob
> >
> > --- In atm_free@yahoogroup s.com, "albireo13" <albireo13@ ..> wrote:
> > >
> > > I guess it boils down between which is harder to make
> > successfully ..... the ellipsoidal DK
> > > primary or the hyperbolopidal CC secondary.
> > >
> > > If I go DK, what techniques have folks used for testing the DK
> > primary?
> > >
> > > Thanks,
> > > Rob
> > >
> > > Rob--- In atm_free@yahoogroup s.com, "Tony Gondola" <acgna@> wrote:
> > > >
> > > > In that case it really sounds like a longer focus DK would be
> > the best
> > > > balance between performance and ease of construction.
> > > >
> > > > Tony
> > > >
> > > > ----- Original Message -----
> > > > From: "albireo13" <albireo13@>
> > > > To: <atm_free@yahoogrou p s.com>
> > > > Sent: Wednesday, December 03, 2008 4:11 PM
> > > > Subject: [atm_free] Re: ATM Cassegrain?
> > > >
> > > >
> > > > > This would strictly be for visual ....
> > lunar/planetary/ doubles.
> > > > > With bigger CO and longer tube, I don't think Gregorian is
> > worth it. I
> > > > > won't use it for
> > > > > terrestrial so a non-inverted view is not important.
> > > > > Hmmm ....
> > > > >
> > > > > Rob
> > > > >
> > > > >
> > > > > --- In atm_free@yahoogroup s.com, "Tony Gondola" <acgna@> wrote:
> > > > >>
> > > > >> Hi Rob,
> > > > >>
> > > > >> Since you're looking at a fairly long focal ratio system
> > (F/15-18) I
> > > > >> wouldn't think that the extended field performance
> > performance would
> > > > >> really
> > > > >> be an issue. Also, keep in mind that a DK primary is simply an
> > > > >> under-corrected Newtonian primary. As you go from a sphere to
> > a parabolic
> > > > >> surface you pass through the shape and correction required
> > for the DK..
> > > > >> It's
> > > > >> usually around a conic constant of -0.8 or 80% of the full
> > correction
> > > > >> you'd
> > > > >> usually apply for a Newtonian primary. You just have to know
> > when to
> > > > >> stop.
> > > > >> Just plug in the correct target conic constant into your test
> > data
> > > > >> reduction
> > > > >> software and you're good to go.
> > > > >>
> > > > >> To answer your question about Gregorian verses DK I ray
> > traced two
> > > > >> systems,
> > > > >> both 6" F/16. The DK gives a diffraction limited FOV of
> > 2.4' , the
> > > > >> Gregorian
> > > > >> gives 24'. Both systems were calculated with F 3.3 primaries.
> > At first
> > > > >> the
> > > > >> Gregorian field looks great but it comes at the expense of a
> > much larger
> > > > >> diameter secondary. Interestingly, it's diffraction limited
> > field
> > > > >> performance is slightly better then an equivalent classical
> > cassegrain
> > > > >> but
> > > > >> you'll pay for that obstruction percentage. I haven't played
> > with that
> > > > >> design enough to know how much that can be reduced but I
> > suspect that
> > > > >> because of the position of the secondary which is outside
> > focus, it will
> > > > >> always be larger then the other designs for an equal amount
> > of field
> > > > >> illumination.
> > > > >>
> > > > >> I think what this really comes down to is what is the scope
> > going to be
> > > > >> used
> > > > >> for? If it's lunar and planetary viewing and imaging you may
> > as well go
> > > > >> with
> > > > >> the DK and extend the f ratio out into the F/22-24 range.That
> > will give
> > > > >> you
> > > > >> enough EFL that you won't need a barlow and the secondary can
> > be kept
> > > > >> small
> > > > >> (sort of the whole point of a long focus cass.) At that F
> > ratio, the
> > > > >> diffraction limited field opens up to almost 4' (plenty for
> > the intended
> > > > >> use) and the image scale is just about perfect in terms of
> > over-sampling
> > > > >> for
> > > > >> diffraction limited imaging without a barlow.
> > > > >>
> > > > >> Tony
> > > > >>
> > > > >>
> > > > >>
> > > > >>
> > > > >>
> > > > >> ----- Original Message -----
> > > > >> From: "albireo13" <albireo13@>
> > > > >> To: <atm_free@yahoogrou p s.com>
> > > > >> Sent: Tuesday, December 02, 2008 5:37 PM
> > > > >> Subject: [atm_free] Re: ATM Cassegrain?
> > > > >>
> > > > >>
> > > > >> > Hi Tony,
> > > > >> > I was leaning towards a classical Cass for two reasons:
> > > > >> >
> > > > >> > 1. it has far better coma performance than a like-f-ratio
> > DK
> > > > >> >
> > > > >> > 2. the primary is a paraboloid. I've done a few newt
> > mirrors so doing
> > > > >> > a
> > > > >> > paraboloid is
> > > > >> > something I understand. Doing an ellipsoid (DK) would be a
> > leap of
> > > > >> > faith
> > > > >> >
> > > > >> > Of course the hyperboloid secondary would be the CC
> > challenge.
> > > > >> >
> > > > >> > I was always intruiged by a gregorian so that would be a
> > neat option
> > > > >> > too.
> > > > >> >
> > > > >> > Any thoughts on how a Greg. would compare to a DK under the
> > stars?
> > > > >> >
> > > > >> > Rob
> > > > >> >
> > > > >> >
> > > > >> > --- In atm_free@yahoogroup s.com, "Tony Gondola" <acgna@>
> > wrote:
> > > > >> >>
> > > > >> >> I make 10" and 12.5" F/24 DK cassegrains on a regular
> > basis. It would
> > > > >> >> be
> > > > >> >> by
> > > > >> >> far the easiest cassegrain type to make. As you know the
> > secondary is
> > > > >> >> spherical and can be easily tested just just polishing out
> > the tool
> > > > >> >> and
> > > > >> >> using that as a test plate. The primary is a bit easier
> > then a good
> > > > >> >> newtonian primary except that you really have to nail the
> > overall
> > > > >> >> correction
> > > > >> >> if you want the best system performance.
> > > > >> >>
> > > > >> >> If tube length isn't a problem you might also consider a
> > gregorian. It
> > > > >> >> also
> > > > >> >> uses a parabolic primary and slightly corrected secondary
> > which is
> > > > >> >> concave
> > > > >> >> so it's also very easy to make and test.
> > > > >> >>
> > > > >> >> Tony
> > > > >> >> BigEye Optics
> > > > >> >>
> > > > >> >>
> > > > >> >>
> > > > >> >> ----- Original Message -----
> > > > >> >> From: "albireo13" <albireo13@>
> > > > >> >> To: <atm_free@yahoogrou p s.com>
> > > > >> >> Sent: Tuesday, December 02, 2008 8:41 AM
> > > > >> >> Subject: [atm_free] ATM Cassegrain?
> > > > >> >>
> > > > >> >>
> > > > >> >> >I have always had the itch to do a ATM Cassegrain ..
> > either Dall-
> > > > >> >> > Kirkham or Classical Cassegrain. I've done a few
> > Newtonian mirrors
> > > > >> >> > so I
> > > > >> >> > can handle paraboloids. The fastest I've done is a
> > f/4.7. This is
> > > > >> >> > a
> > > > >> >> > modest size scope for visual use only, maybe 6-8"
> > aperture and
> > > > >> >> > f/15-18.
> > > > >> >> >
> > > > >> >> > Any thoughts on which would be easier to complete? Any
> > hidden
> > > > >> >> > pitfalls? I'd love to hear from others who have
> > caompleted one.
> > > > >> >> >
> > > > >> >> >
> > > > >> >> > Thanks,
> > > > >> >> > Rob
> > > > >> >> >
> > > > >> >> >
> > > > >> >> >
> > > > >> >> > ------------ --------- --------- ------
> > > > >> >> >
> > > > >> >> > Yahoo! Groups Links
> > > > >> >> >
> > > > >> >> >
> > > > >> >> >
> > > > >> >>
> > > > >> >>
> > > > >> >> ------------ --------- --------- --------- ---------
> --------- -
> > --
> > > ---
> > > > > ---
> > > > >> > ------------ -
> > > > >> >>
> > > > >> >>
> > > > >> >>
> > > > >> >> No virus found in this incoming message.
> > > > >> >> Checked by AVG - http://www.avg. com
> > > > >> >> Version: 8.0.176 / Virus Database: 270.9.12/1824 - Release
> > Date:
> > > > >> >> 12/2/2008
> > > > >> >> 9:31 AM
> > > > >> >>
> > > > >> >
> > > > >> >
> > > > >> >
> > > > >> >
> > > > >> > ------------ --------- --------- ------
> > > > >> >
> > > > >> > Yahoo! Groups Links
> > > > >> >
> > > > >> >
> > > > >> >
> > > > >>
> > > > >>
> > > > >> ------------ --------- --------- --------- ---------
--------- -
> > --
> > > ---
> > > > > ------------ -
> > > > >>
> > > > >>
> > > > >>
> > > > >> No virus found in this incoming message.
> > > > >> Checked by AVG - http://www.avg. com
> > > > >> Version: 8.0.176 / Virus Database: 270.9.13/1825 - Release
> > Date:
> > > > >> 12/2/2008
> > > > >> 8:44 PM
> > > > >>
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > ------------ --------- --------- ------
> > > > >
> > > > > Yahoo! Groups Links
> > > > >
> > > > >
> > > > >
> > > >
> > > >
> > > > ------------ --------- --------- --------- --------- --------- -
> > --
> > > ------------ -
> > > >
> > > >
> > > >
> > > > No virus found in this incoming message.
> > > > Checked by AVG - http://www.avg. com
> > > > Version: 8.0.176 / Virus Database: 270.9.13/1827 - Release Date:
> > 12/3/2008
> > > > 5:41 PM
> > > >
> > >
> >
>

On tilt and decentering etc you might be able to do something with
winspot. It's a tct telescope design program and very easy to use.
Olso lt will also do that sort of thing but don't ask me how.

Being fair to DK's most books that mention them point out that they
have considerably more coma than conventional cas designs and then go
on to say that they are primarily planetary scopes and on that basis
it doesn't matter. Miss match the curves though and things are going
to be worse. Get them correct and one is likely to end up with a
decent scope as the comments on coma relate to straight cass's f20 and
or even more. Many peoples use f4 and even lower newts and are
entirely happy with them despite the high levels of coma. An f20 cas
has the same amount of coma as an f20 newt - hardly any at all. One
thing I have always wondered about in this area is raliegh limit
spherical mirrors. Is there an all spherical cass that meets or
exceeds that limit? There should be.

John

--- In atm_free@yahoogroups.com, "Tony Gondola" <acgna@...> wrote:
>
> I would 2nd that comment. The primary correction needs to be held
within +_
> 0.01% correction and that's usually with a primary that's F/4 or
faster.
> Also the RC of both the primary and secondary have to be close to
the design
> values, especially if you have little room for error in the final
back focus
> position.  In short, a DK is the easiest cass. to make but the level of
> difficulty is certainly much higher then a Newtonian, especially if the
> Newtonian is of moderate focal ratio and RC only needs to be in the
> ballpark. If you're not confident of being able to hold the tolerances
> you'll be much better off with a Newtonian and barlow.
>
> Tony
> BigEye Optics
>
>
> ----- Original Message -----
> From: "a.johnw" <a.johnw@...>
> To: <atm_free@yahoogroups.com>
> Sent: Wednesday, December 31, 2008 9:09 AM
> Subject: [atm_free] Re: ATM Cassegrain?
>
>
> Comments about the ease of making a dk often don't point out that the
> radius of curvature of the 2ndry  needs to be very closely matched to
> the figure of the primary. The only truly easy thing about them is the
> lack of the need for a complicated 2ndry mirror test. The primary can
> also be null figured if reqd. Some would advise making the 2ndry 1st
> and then a primary to match/
>
> John
>
> --- In atm_free@yahoogroups.com, lance clarke <alaskawolfjoe@> wrote:
> >
> > The DK is easier to make both optically and mechanically. For the
> secondary, you just make the secondary tool into a spherical test
> plate (foucault null test this), and then use it to fringe test the
> secondary mirror. As for figuring the primary of a DK, the elipsoid
> is actually easier to figure than a parabola, or at least that was my
> experience.
> >
> > Lance
> >
> >
> >
> >
> > ________________________________
> > From: albireo13 <albireo13@>
> > To: atm_free@yahoogroups.com
> > Sent: Thursday, December 4, 2008 1:31:55 PM
> > Subject: [atm_free] Re: ATM Cassegrain?
> >
> >
> > Hmmm ... I'd like to play around with a SW simulator to check
> > sensitivity of a design to variations in tilt and separation.
> > I'm not a precision machinest so the mechanical construction issues
> > may drive me to favor one design over another.
> >
> > Can anyone suggest a sw program for simulating Cass. optical
> > systems? Something relatively basic, with spot diagram output would
> > be nice. So far I've been using CassDes by Mike Jones. It comes
> > up with designs and generates spot diagrams ... quite nice.
> > However, it doesn't let you modify spacings, etc to test effects on
> > the focal plane spot diagram.
> >
> > Rob
> >
> > --- In atm_free@yahoogroup s.com, "albireo13" <albireo13@ ..> wrote:
> > >
> > > I guess it boils down between which is harder to make
> > successfully .... the ellipsoidal DK
> > > primary or the hyperbolopidal CC secondary.
> > >
> > > If I go DK, what techniques have folks used for testing the DK
> > primary?
> > >
> > > Thanks,
> > > Rob
> > >
> > > Rob--- In atm_free@yahoogroup s.com, "Tony Gondola" <acgna@> wrote:
> > > >
> > > > In that case it really sounds like a longer focus DK would be
> > the best
> > > > balance between performance and ease of construction.
> > > >
> > > > Tony
> > > >
> > > > ----- Original Message -----
> > > > From: "albireo13" <albireo13@>
> > > > To: <atm_free@yahoogroup s.com>
> > > > Sent: Wednesday, December 03, 2008 4:11 PM
> > > > Subject: [atm_free] Re: ATM Cassegrain?
> > > >
> > > >
> > > > > This would strictly be for visual ....
> > lunar/planetary/ doubles.
> > > > > With bigger CO and longer tube, I don't think Gregorian is
> > worth it. I
> > > > > won't use it for
> > > > > terrestrial so a non-inverted view is not important.
> > > > > Hmmm ....
> > > > >
> > > > > Rob
> > > > >
> > > > >
> > > > > --- In atm_free@yahoogroup s.com, "Tony Gondola" <acgna@> wrote:
> > > > >>
> > > > >> Hi Rob,
> > > > >>
> > > > >> Since you're looking at a fairly long focal ratio system
> > (F/15-18) I
> > > > >> wouldn't think that the extended field performance
> > performance would
> > > > >> really
> > > > >> be an issue. Also, keep in mind that a DK primary is simply an
> > > > >> under-corrected Newtonian primary. As you go from a sphere to
> > a parabolic
> > > > >> surface you pass through the shape and correction required
> > for the DK.
> > > > >> It's
> > > > >> usually around a conic constant of -0.8 or 80% of the full
> > correction
> > > > >> you'd
> > > > >> usually apply for a Newtonian primary. You just have to know
> > when to
> > > > >> stop.
> > > > >> Just plug in the correct target conic constant into your test
> > data
> > > > >> reduction
> > > > >> software and you're good to go.
> > > > >>
> > > > >> To answer your question about Gregorian verses DK I ray
> > traced two
> > > > >> systems,
> > > > >> both 6" F/16. The DK gives a diffraction limited FOV of
> > 2.4' , the
> > > > >> Gregorian
> > > > >> gives 24'. Both systems were calculated with F 3.3 primaries.
> > At first
> > > > >> the
> > > > >> Gregorian field looks great but it comes at the expense of a
> > much larger
> > > > >> diameter secondary. Interestingly, it's diffraction limited
> > field
> > > > >> performance is slightly better then an equivalent classical
> > cassegrain
> > > > >> but
> > > > >> you'll pay for that obstruction percentage. I haven't played
> > with that
> > > > >> design enough to know how much that can be reduced but I
> > suspect that
> > > > >> because of the position of the secondary which is outside
> > focus, it will
> > > > >> always be larger then the other designs for an equal amount
> > of field
> > > > >> illumination.
> > > > >>
> > > > >> I think what this really comes down to is what is the scope
> > going to be
> > > > >> used
> > > > >> for? If it's lunar and planetary viewing and imaging you may
> > as well go
> > > > >> with
> > > > >> the DK and extend the f ratio out into the F/22-24 range.That
> > will give
> > > > >> you
> > > > >> enough EFL that you won't need a barlow and the secondary can
> > be kept
> > > > >> small
> > > > >> (sort of the whole point of a long focus cass.) At that F
> > ratio, the
> > > > >> diffraction limited field opens up to almost 4' (plenty for
> > the intended
> > > > >> use) and the image scale is just about perfect in terms of
> > over-sampling
> > > > >> for
> > > > >> diffraction limited imaging without a barlow.
> > > > >>
> > > > >> Tony
> > > > >>
> > > > >>
> > > > >>
> > > > >>
> > > > >>
> > > > >> ----- Original Message -----
> > > > >> From: "albireo13" <albireo13@>
> > > > >> To: <atm_free@yahoogroup s.com>
> > > > >> Sent: Tuesday, December 02, 2008 5:37 PM
> > > > >> Subject: [atm_free] Re: ATM Cassegrain?
> > > > >>
> > > > >>
> > > > >> > Hi Tony,
> > > > >> > I was leaning towards a classical Cass for two reasons:
> > > > >> >
> > > > >> > 1. it has far better coma performance than a like-f-ratio
> > DK
> > > > >> >
> > > > >> > 2. the primary is a paraboloid. I've done a few newt
> > mirrors so doing
> > > > >> > a
> > > > >> > paraboloid is
> > > > >> > something I understand. Doing an ellipsoid (DK) would be a
> > leap of
> > > > >> > faith
> > > > >> >
> > > > >> > Of course the hyperboloid secondary would be the CC
> > challenge.
> > > > >> >
> > > > >> > I was always intruiged by a gregorian so that would be a
> > neat option
> > > > >> > too.
> > > > >> >
> > > > >> > Any thoughts on how a Greg. would compare to a DK under the
> > stars?
> > > > >> >
> > > > >> > Rob
> > > > >> >
> > > > >> >
> > > > >> > --- In atm_free@yahoogroup s.com, "Tony Gondola" <acgna@>
> > wrote:
> > > > >> >>
> > > > >> >> I make 10" and 12.5" F/24 DK cassegrains on a regular
> > basis. It would
> > > > >> >> be
> > > > >> >> by
> > > > >> >> far the easiest cassegrain type to make. As you know the
> > secondary is
> > > > >> >> spherical and can be easily tested just just polishing out
> > the tool
> > > > >> >> and
> > > > >> >> using that as a test plate. The primary is a bit easier
> > then a good
> > > > >> >> newtonian primary except that you really have to nail the
> > overall
> > > > >> >> correction
> > > > >> >> if you want the best system performance.
> > > > >> >>
> > > > >> >> If tube length isn't a problem you might also consider a
> > gregorian. It
> > > > >> >> also
> > > > >> >> uses a parabolic primary and slightly corrected secondary
> > which is
> > > > >> >> concave
> > > > >> >> so it's also very easy to make and test.
> > > > >> >>
> > > > >> >> Tony
> > > > >> >> BigEye Optics
> > > > >> >>
> > > > >> >>
> > > > >> >>
> > > > >> >> ----- Original Message -----
> > > > >> >> From: "albireo13" <albireo13@>
> > > > >> >> To: <atm_free@yahoogroup s.com>
> > > > >> >> Sent: Tuesday, December 02, 2008 8:41 AM
> > > > >> >> Subject: [atm_free] ATM Cassegrain?
> > > > >> >>
> > > > >> >>
> > > > >> >> >I have always had the itch to do a ATM Cassegrain ..
> > either Dall-
> > > > >> >> > Kirkham or Classical Cassegrain. I've done a few
> > Newtonian mirrors
> > > > >> >> > so I
> > > > >> >> > can handle paraboloids. The fastest I've done is a
> > f/4.7. This is
> > > > >> >> > a
> > > > >> >> > modest size scope for visual use only, maybe 6-8"
> > aperture and
> > > > >> >> > f/15-18.
> > > > >> >> >
> > > > >> >> > Any thoughts on which would be easier to complete? Any
> > hidden
> > > > >> >> > pitfalls? I'd love to hear from others who have
> > caompleted one.
> > > > >> >> >
> > > > >> >> >
> > > > >> >> > Thanks,
> > > > >> >> > Rob
> > > > >> >> >
> > > > >> >> >
> > > > >> >> >
> > > > >> >> > ------------ --------- --------- ------
> > > > >> >> >
> > > > >> >> > Yahoo! Groups Links
> > > > >> >> >
> > > > >> >> >
> > > > >> >> >
> > > > >> >>
> > > > >> >>
> > > > >> >> ------------ --------- --------- --------- ---------
> --------- -
> > --
> > > ---
> > > > > ---
> > > > >> > ------------ -
> > > > >> >>
> > > > >> >>
> > > > >> >>
> > > > >> >> No virus found in this incoming message.
> > > > >> >> Checked by AVG - http://www.avg. com
> > > > >> >> Version: 8.0.176 / Virus Database: 270.9.12/1824 - Release
> > Date:
> > > > >> >> 12/2/2008
> > > > >> >> 9:31 AM
> > > > >> >>
> > > > >> >
> > > > >> >
> > > > >> >
> > > > >> >
> > > > >> > ------------ --------- --------- ------
> > > > >> >
> > > > >> > Yahoo! Groups Links
> > > > >> >
> > > > >> >
> > > > >> >
> > > > >>
> > > > >>
> > > > >> ------------ --------- --------- --------- ---------
--------- -
> > --
> > > ---
> > > > > ------------ -
> > > > >>
> > > > >>
> > > > >>
> > > > >> No virus found in this incoming message.
> > > > >> Checked by AVG - http://www.avg. com
> > > > >> Version: 8.0.176 / Virus Database: 270.9.13/1825 - Release
> > Date:
> > > > >> 12/2/2008
> > > > >> 8:44 PM
> > > > >>
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > ------------ --------- --------- ------
> > > > >
> > > > > Yahoo! Groups Links
> > > > >
> > > > >
> > > > >
> > > >
> > > >
> > > > ------------ --------- --------- --------- --------- --------- -
> > --
> > > ------------ -
> > > >
> > > >
> > > >
> > > > No virus found in this incoming message.
> > > > Checked by AVG - http://www.avg. com
> > > > Version: 8.0.176 / Virus Database: 270.9.13/1827 - Release Date:
> > 12/3/2008
> > > > 5:41 PM
> > > >
> > >
> >
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>
>
>
>
--------------------------------------------------------------------------------
>
>
>
> No virus found in this incoming message.
> Checked by AVG - http://www.avg.com
> Version: 8.0.176 / Virus Database: 270.10.1/1870 - Release Date:
12/31/2008
> 8:44 AM
>

All of the DK sets I've made have been longer the F/20, used almost
exclusively for lunar and planetary imaging where the camera chips are
typically small enough that off axis aberrations really don't come into
play.

On all spherical cass designs I don't think you can do it with just two
surfaces, The closest I can think of is the Pressmann-Camichel. It uses a
spherical primary and a hyperbolic secondary. Not all spherical but at least
all the correction is in the small element. Thing is, it's a whopping amount
of correction around -6.0. If you want talk all spherical surfaces the
simplest I can think of  would be a long focus Gregory Maksutov, just three
surfaces, all spherical. The downside is the cost of BK7 in larger diameters
but manufacture would be fairly easy.

To my mind, the most interesting DK designs are the type that use a two
element corrector group near focus. Some of these can deliver large
diffraction limited fields at reasonable focal ratios.

I'm sure there's much I've missed here design wise but that's all that I can
pull off the top of my head at the moment.

Tony
BigEye Optics



----- Original Message -----
From: "a.johnw" <a.johnw@...>
To: <atm_free@yahoogroups.com>
Sent: Sunday, January 04, 2009 12:06 PM
Subject: [atm_free] Re: ATM Cassegrain?


> On tilt and decentering etc you might be able to do something with
> winspot. It's a tct telescope design program and very easy to use.
> Olso lt will also do that sort of thing but don't ask me how.
>
> Being fair to DK's most books that mention them point out that they
> have considerably more coma than conventional cas designs and then go
> on to say that they are primarily planetary scopes and on that basis
> it doesn't matter. Miss match the curves though and things are going
> to be worse. Get them correct and one is likely to end up with a
> decent scope as the comments on coma relate to straight cass's f20 and
> or even more. Many peoples use f4 and even lower newts and are
> entirely happy with them despite the high levels of coma. An f20 cas
> has the same amount of coma as an f20 newt - hardly any at all. One
> thing I have always wondered about in this area is raliegh limit
> spherical mirrors. Is there an all spherical cass that meets or
> exceeds that limit? There should be.
>
> John
>
> --- In atm_free@yahoogroups.com, "Tony Gondola" <acgna@...> wrote:
>>
>> I would 2nd that comment. The primary correction needs to be held
> within +_
>> 0.01% correction and that's usually with a primary that's F/4 or
> faster.
>> Also the RC of both the primary and secondary have to be close to
> the design
>> values, especially if you have little room for error in the final
> back focus
>> position.  In short, a DK is the easiest cass. to make but the level of
>> difficulty is certainly much higher then a Newtonian, especially if the
>> Newtonian is of moderate focal ratio and RC only needs to be in the
>> ballpark. If you're not confident of being able to hold the tolerances
>> you'll be much better off with a Newtonian and barlow.
>>
>> Tony
>> BigEye Optics
>>
>>
>> ----- Original Message -----
>> From: "a.johnw" <a.johnw@...>
>> To: <atm_free@yahoogroups.com>
>> Sent: Wednesday, December 31, 2008 9:09 AM
>> Subject: [atm_free] Re: ATM Cassegrain?
>>
>>
>> Comments about the ease of making a dk often don't point out that the
>> radius of curvature of the 2ndry  needs to be very closely matched to
>> the figure of the primary. The only truly easy thing about them is the
>> lack of the need for a complicated 2ndry mirror test. The primary can
>> also be null figured if reqd. Some would advise making the 2ndry 1st
>> and then a primary to match/
>>
>> John
>>
>> --- In atm_free@yahoogroups.com, lance clarke <alaskawolfjoe@> wrote:
>> >
>> > The DK is easier to make both optically and mechanically. For the
>> secondary, you just make the secondary tool into a spherical test
>> plate (foucault null test this), and then use it to fringe test the
>> secondary mirror. As for figuring the primary of a DK, the elipsoid
>> is actually easier to figure than a parabola, or at least that was my
>> experience.
>> >
>> > Lance
>> >
>> >
>> >
>> >
>> > ________________________________
>> > From: albireo13 <albireo13@>
>> > To: atm_free@yahoogroups.com
>> > Sent: Thursday, December 4, 2008 1:31:55 PM
>> > Subject: [atm_free] Re: ATM Cassegrain?
>> >
>> >
>> > Hmmm ... I'd like to play around with a SW simulator to check
>> > sensitivity of a design to variations in tilt and separation.
>> > I'm not a precision machinest so the mechanical construction issues
>> > may drive me to favor one design over another.
>> >
>> > Can anyone suggest a sw program for simulating Cass. optical
>> > systems? Something relatively basic, with spot diagram output would
>> > be nice. So far I've been using CassDes by Mike Jones. It comes
>> > up with designs and generates spot diagrams ... quite nice.
>> > However, it doesn't let you modify spacings, etc to test effects on
>> > the focal plane spot diagram.
>> >
>> > Rob
>> >
>> > --- In atm_free@yahoogroup s.com, "albireo13" <albireo13@ ..> wrote:
>> > >
>> > > I guess it boils down between which is harder to make
>> > successfully .... the ellipsoidal DK
>> > > primary or the hyperbolopidal CC secondary.
>> > >
>> > > If I go DK, what techniques have folks used for testing the DK
>> > primary?
>> > >
>> > > Thanks,
>> > > Rob
>> > >
>> > > Rob--- In atm_free@yahoogroup s.com, "Tony Gondola" <acgna@> wrote:
>> > > >
>> > > > In that case it really sounds like a longer focus DK would be
>> > the best
>> > > > balance between performance and ease of construction.
>> > > >
>> > > > Tony
>> > > >
>> > > > ----- Original Message -----
>> > > > From: "albireo13" <albireo13@>
>> > > > To: <atm_free@yahoogroup s.com>
>> > > > Sent: Wednesday, December 03, 2008 4:11 PM
>> > > > Subject: [atm_free] Re: ATM Cassegrain?
>> > > >
>> > > >
>> > > > > This would strictly be for visual ....
>> > lunar/planetary/ doubles.
>> > > > > With bigger CO and longer tube, I don't think Gregorian is
>> > worth it. I
>> > > > > won't use it for
>> > > > > terrestrial so a non-inverted view is not important.
>> > > > > Hmmm ....
>> > > > >
>> > > > > Rob
>> > > > >
>> > > > >
>> > > > > --- In atm_free@yahoogroup s.com, "Tony Gondola" <acgna@> wrote:
>> > > > >>
>> > > > >> Hi Rob,
>> > > > >>
>> > > > >> Since you're looking at a fairly long focal ratio system
>> > (F/15-18) I
>> > > > >> wouldn't think that the extended field performance
>> > performance would
>> > > > >> really
>> > > > >> be an issue. Also, keep in mind that a DK primary is simply an
>> > > > >> under-corrected Newtonian primary. As you go from a sphere to
>> > a parabolic
>> > > > >> surface you pass through the shape and correction required
>> > for the DK.
>> > > > >> It's
>> > > > >> usually around a conic constant of -0.8 or 80% of the full
>> > correction
>> > > > >> you'd
>> > > > >> usually apply for a Newtonian primary. You just have to know
>> > when to
>> > > > >> stop.
>> > > > >> Just plug in the correct target conic constant into your test
>> > data
>> > > > >> reduction
>> > > > >> software and you're good to go.
>> > > > >>
>> > > > >> To answer your question about Gregorian verses DK I ray
>> > traced two
>> > > > >> systems,
>> > > > >> both 6" F/16. The DK gives a diffraction limited FOV of
>> > 2.4' , the
>> > > > >> Gregorian
>> > > > >> gives 24'. Both systems were calculated with F 3.3 primaries.
>> > At first
>> > > > >> the
>> > > > >> Gregorian field looks great but it comes at the expense of a
>> > much larger
>> > > > >> diameter secondary. Interestingly, it's diffraction limited
>> > field
>> > > > >> performance is slightly better then an equivalent classical
>> > cassegrain
>> > > > >> but
>> > > > >> you'll pay for that obstruction percentage. I haven't played
>> > with that
>> > > > >> design enough to know how much that can be reduced but I
>> > suspect that
>> > > > >> because of the position of the secondary which is outside
>> > focus, it will
>> > > > >> always be larger then the other designs for an equal amount
>> > of field
>> > > > >> illumination.
>> > > > >>
>> > > > >> I think what this really comes down to is what is the scope
>> > going to be
>> > > > >> used
>> > > > >> for? If it's lunar and planetary viewing and imaging you may
>> > as well go
>> > > > >> with
>> > > > >> the DK and extend the f ratio out into the F/22-24 range.That
>> > will give
>> > > > >> you
>> > > > >> enough EFL that you won't need a barlow and the secondary can
>> > be kept
>> > > > >> small
>> > > > >> (sort of the whole point of a long focus cass.) At that F
>> > ratio, the
>> > > > >> diffraction limited field opens up to almost 4' (plenty for
>> > the intended
>> > > > >> use) and the image scale is just about perfect in terms of
>> > over-sampling
>> > > > >> for
>> > > > >> diffraction limited imaging without a barlow.
>> > > > >>
>> > > > >> Tony
>> > > > >>
>> > > > >>
>> > > > >>
>> > > > >>
>> > > > >>
>> > > > >> ----- Original Message -----
>> > > > >> From: "albireo13" <albireo13@>
>> > > > >> To: <atm_free@yahoogroup s.com>
>> > > > >> Sent: Tuesday, December 02, 2008 5:37 PM
>> > > > >> Subject: [atm_free] Re: ATM Cassegrain?
>> > > > >>
>> > > > >>
>> > > > >> > Hi Tony,
>> > > > >> > I was leaning towards a classical Cass for two reasons:
>> > > > >> >
>> > > > >> > 1. it has far better coma performance than a like-f-ratio
>> > DK
>> > > > >> >
>> > > > >> > 2. the primary is a paraboloid. I've done a few newt
>> > mirrors so doing
>> > > > >> > a
>> > > > >> > paraboloid is
>> > > > >> > something I understand. Doing an ellipsoid (DK) would be a
>> > leap of
>> > > > >> > faith
>> > > > >> >
>> > > > >> > Of course the hyperboloid secondary would be the CC
>> > challenge.
>> > > > >> >
>> > > > >> > I was always intruiged by a gregorian so that would be a
>> > neat option
>> > > > >> > too.
>> > > > >> >
>> > > > >> > Any thoughts on how a Greg. would compare to a DK under the
>> > stars?
>> > > > >> >
>> > > > >> > Rob
>> > > > >> >
>> > > > >> >
>> > > > >> > --- In atm_free@yahoogroup s.com, "Tony Gondola" <acgna@>
>> > wrote:
>> > > > >> >>
>> > > > >> >> I make 10" and 12.5" F/24 DK cassegrains on a regular
>> > basis. It would
>> > > > >> >> be
>> > > > >> >> by
>> > > > >> >> far the easiest cassegrain type to make. As you know the
>> > secondary is
>> > > > >> >> spherical and can be easily tested just just polishing out
>> > the tool
>> > > > >> >> and
>> > > > >> >> using that as a test plate. The primary is a bit easier
>> > then a good
>> > > > >> >> newtonian primary except that you really have to nail the
>> > overall
>> > > > >> >> correction
>> > > > >> >> if you want the best system performance.
>> > > > >> >>
>> > > > >> >> If tube length isn't a problem you might also consider a
>> > gregorian. It
>> > > > >> >> also
>> > > > >> >> uses a parabolic primary and slightly corrected secondary
>> > which is
>> > > > >> >> concave
>> > > > >> >> so it's also very easy to make and test.
>> > > > >> >>
>> > > > >> >> Tony
>> > > > >> >> BigEye Optics
>> > > > >> >>
>> > > > >> >>
>> > > > >> >>
>> > > > >> >> ----- Original Message -----
>> > > > >> >> From: "albireo13" <albireo13@>
>> > > > >> >> To: <atm_free@yahoogroup s.com>
>> > > > >> >> Sent: Tuesday, December 02, 2008 8:41 AM
>> > > > >> >> Subject: [atm_free] ATM Cassegrain?
>> > > > >> >>
>> > > > >> >>
>> > > > >> >> >I have always had the itch to do a ATM Cassegrain ..
>> > either Dall-
>> > > > >> >> > Kirkham or Classical Cassegrain. I've done a few
>> > Newtonian mirrors
>> > > > >> >> > so I
>> > > > >> >> > can handle paraboloids. The fastest I've done is a
>> > f/4.7. This is
>> > > > >> >> > a
>> > > > >> >> > modest size scope for visual use only, maybe 6-8"
>> > aperture and
>> > > > >> >> > f/15-18.
>> > > > >> >> >
>> > > > >> >> > Any thoughts on which would be easier to complete? Any
>> > hidden
>> > > > >> >> > pitfalls? I'd love to hear from others who have
>> > caompleted one.
>> > > > >> >> >
>> > > > >> >> >
>> > > > >> >> > Thanks,
>> > > > >> >> > Rob
>> > > > >> >> >
>> > > > >> >> >
>> > > > >> >> >
>> > > > >> >> > ------------ --------- --------- ------
>> > > > >> >> >
>> > > > >> >> > Yahoo! Groups Links
>> > > > >> >> >
>> > > > >> >> >
>> > > > >> >> >
>> > > > >> >>
>> > > > >> >>
>> > > > >> >> ------------ --------- --------- --------- ---------
>> --------- -
>> > --
>> > > ---
>> > > > > ---
>> > > > >> > ------------ -
>> > > > >> >>
>> > > > >> >>
>> > > > >> >>
>> > > > >> >> No virus found in this incoming message.
>> > > > >> >> Checked by AVG - http://www.avg. com
>> > > > >> >> Version: 8.0.176 / Virus Database: 270.9.12/1824 - Release
>> > Date:
>> > > > >> >> 12/2/2008
>> > > > >> >> 9:31 AM
>> > > > >> >>
>> > > > >> >
>> > > > >> >
>> > > > >> >
>> > > > >> >
>> > > > >> > ------------ --------- --------- ------
>> > > > >> >
>> > > > >> > Yahoo! Groups Links
>> > > > >> >
>> > > > >> >
>> > > > >> >
>> > > > >>
>> > > > >>
>> > > > >> ------------ --------- --------- --------- ---------
> --------- -
>> > --
>> > > ---
>> > > > > ------------ -
>> > > > >>
>> > > > >>
>> > > > >>
>> > > > >> No virus found in this incoming message.
>> > > > >> Checked by AVG - http://www.avg. com
>> > > > >> Version: 8.0.176 / Virus Database: 270.9.13/1825 - Release
>> > Date:
>> > > > >> 12/2/2008
>> > > > >> 8:44 PM
>> > > > >>
>> > > > >
>> > > > >
>> > > > >
>> > > > >
>> > > > > ------------ --------- --------- ------
>> > > > >
>> > > > > Yahoo! Groups Links
>> > > > >
>> > > > >
>> > > > >
>> > > >
>> > > >
>> > > > ------------ --------- --------- --------- --------- --------- -
>> > --
>> > > ------------ -
>> > > >
>> > > >
>> > > >
>> > > > No virus found in this incoming message.
>> > > > Checked by AVG - http://www.avg. com
>> > > > Version: 8.0.176 / Virus Database: 270.9.13/1827 - Release Date:
>> > 12/3/2008
>> > > > 5:41 PM
>> > > >
>> > >
>> >
>>
>>
>>
>> ------------------------------------
>>
>> Yahoo! Groups Links
>>
>>
>>
>>
>>
>>
>
--------------------------------------------------------------------------------
>>
>>
>>
>> No virus found in this incoming message.
>> Checked by AVG - http://www.avg.com
>> Version: 8.0.176 / Virus Database: 270.10.1/1870 - Release Date:
> 12/31/2008
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> ------------------------------------
>
> Yahoo! Groups Links
>
>
>


--------------------------------------------------------------------------------



No virus found in this incoming message.
Checked by AVG - http://www.avg.com
Version: 8.0.176 / Virus Database: 270.10.2/1876 - Release Date: 1/5/2009
9:44 AM

>>>
To my mind, the most interesting DK designs are the type that use a two
element corrector group near focus. Some of these can deliver large
diffraction limited fields at reasonable focal ratios.
<<<


Another idea that intrigues me is the 4 mirror design.  Two large mirrors
which can be both spherical (or both parabolic) act to produce a parallel
beam of light that is then imaged by two more mirrors, with the correction
dumped (~12x over corrected) into the 3rd much smaller mirror (4th mirror is
smallest yet).  The whole design can be quite fast and quite compact (think
of the mirrors sitting in the edges of a box).  See Schroeder's Astronomical
Optics, the chapter on 4 mirror designs.

Mel Bartels

I picked up two 127mm f5.5 objectives this week and I plan on building
a big bino. I'm looking for two 1 1/4" helical focusers for the
project. I've looked all over the web but haven't found any. These were
fairly common 5+ years ago but seem scarcer than hens teeth nowadays.

Does any one know of a company selling them?

--- In atm_free@yahoogroups.com, "Greg" <starguy@...> wrote:
>
> I picked up two 127mm f5.5 objectives this week and I plan on
building
> a big bino. I'm looking for two 1 1/4" helical focusers for the
> project. I've looked all over the web but haven't found any. These
were
> fairly common 5+ years ago but seem scarcer than hens teeth nowadays.
>
> Does any one know of a company selling them?
>

Do any of these help? (you can go direct to Hutech)

http://www.sciencecenter.net/hutech/borg/focuser.htm

Tom

That sounds like one of the tilted component designs based on I think
a corrector by Baker. If so a design comes with winspot but a close
examination shows that the mirrors interfere with the light path. The
spot diagram is spectacular over a very wide field neglecting the
light path problems. Is this arrangement different Mel? There is also
a German patent on a 4 mirror design but so far I've had no luck with it.

John

--- In atm_free@yahoogroups.com, "Mel Bartels" <mbartels@...> wrote:
>
> >>>
> To my mind, the most interesting DK designs are the type that use a two
> element corrector group near focus. Some of these can deliver large
> diffraction limited fields at reasonable focal ratios.
> <<<
>
>
> Another idea that intrigues me is the 4 mirror design.  Two large
mirrors
> which can be both spherical (or both parabolic) act to produce a
parallel
> beam of light that is then imaged by two more mirrors, with the
correction
> dumped (~12x over corrected) into the 3rd much smaller mirror (4th
mirror is
> smallest yet).  The whole design can be quite fast and quite compact
(think
> of the mirrors sitting in the edges of a box).  See Schroeder's
Astronomical
> Optics, the chapter on 4 mirror designs.
>
> Mel Bartels
>

Celestron conversion

----------------------------------------------------------------------
----------

Hi,

This is my first post here and I will unashamedly admit I am seeking
advice and what better repository of knowledge could there be then
among the ATM community.

Due to an unhappy accident my beloved Celestron 9.25 has been left
devoid of a corrector plate and have deen advised to throw what is
left away, considering that the primary and secondary mirrors are in
perfect condition I feel loath to do this.

My thoughts turned to examples turned out from manufacturers such as
Tal, Vixen and Orion Optics that produce sub aperture designs that
utilise spherical aberration correction components either in front of
the secondary or further down the optical train.

Curiosity has led me to fabricating a secondary spider just to see
with my own eyes just how much spherical aberration is present
without the schmidt plate. (not completed yet), but my problem is how
would you determine the prescription for say a meniscus lens placed
in front of the secondary or a doublet or triplet set at the exit
pupil.

My reasoning is that these components are smaller and easier to
manufacture then a full aperture aspheriser's so may lead to a more
econonomic adaptation for a useful life of the remains.

The ideal scenario of course would be if I could make use of off the
shelf elements as that would contribute to the notion of economic
repair although without the specifications aquisition or manufacture
is academic.

So the sticking point seems to be how to calculate what is needed,
any suggestions would be happily received.

Hi; Measure the diameter of your tube I have made a vaccuum box
to do a 10 inch corrector plate. Email me if you want to borrow it.
Newport Glass carry the glass and you can have them cut it to the
correct diameter for your tube. Gordon

--- In atm_free@yahoogroups.com, "nddxc06" <nddxc06@...> wrote:
>
>  Celestron conversion
>
> --------------------------------------------------------------------
--
> ----------
>
> Hi,
>
> This is my first post here and I will unashamedly admit I am
seeking
> advice and what better repository of knowledge could there be then
> among the ATM community.
>
> Due to an unhappy accident my beloved Celestron 9.25 has been left
> devoid of a corrector plate and have deen advised to throw what is
> left away, considering that the primary and secondary mirrors are
in
> perfect condition I feel loath to do this.
>
> My thoughts turned to examples turned out from manufacturers such
as
> Tal, Vixen and Orion Optics that produce sub aperture designs that
> utilise spherical aberration correction components either in front
of
> the secondary or further down the optical train.
>
> Curiosity has led me to fabricating a secondary spider just to see
> with my own eyes just how much spherical aberration is present
> without the schmidt plate. (not completed yet), but my problem is
how
> would you determine the prescription for say a meniscus lens placed
> in front of the secondary or a doublet or triplet set at the exit
> pupil.
>
> My reasoning is that these components are smaller and easier to
> manufacture then a full aperture aspheriser's so may lead to a more
> econonomic adaptation for a useful life of the remains.
>
> The ideal scenario of course would be if I could make use of off
the
> shelf elements as that would contribute to the notion of economic
> repair although without the specifications aquisition or
manufacture
> is academic.
>
> So the sticking point seems to be how to calculate what is needed,
> any suggestions would be happily received.
>

>>>
That sounds like one of the tilted component designs based on I think
a corrector by Baker. If so a design comes with winspot but a close
examination shows that the mirrors interfere with the light path. The
spot diagram is spectacular over a very wide field neglecting the
light path problems. Is this arrangement different Mel? There is also
a German patent on a 4 mirror design but so far I've had no luck with it.
<<<


These are 4 mirror 2 axis optical configurations, on axis beams, ala
Paul-Schmidt design.  The design that Schroeder considers is for a 16m (!)
aperture with f/1.5 primary, a secondary that's 4m at f/1.5, the tertiary ~
3m at f/4.5 and so forth.  In this design the 4th mirror is strongly
hyperbolic (13x).  He says that an optimized design can achieve 0.2 arc
second image sizes over a 18 arc minute (!) field.  This is from Schroeder's
Astronomical Optics, 2 ed, page 154-.

He lists as one of the references

Wilson, R. and Delabre. B. ('97) Publication Astronomical Society Pacific,
109:53.

Mel Bartels

Hi Gordon,

Thank you for taking the time to reply to my thread.

I admire your skill if you have already produced the vacuum box for
making a corrector plate you sound as if you mean business.

If I understand the process correctly once you have created the right
shape from the vacuum box the plate has to be figured or gound to the
final configuration but how do you know what shape and configuration
is needed ?

I presume the hole for the secondary mount is cut into the glass
after vacuum forming and before figuring, how is the hole cut ?

I have to admit I have never figured glass before and I am not sure I
could aquire the skills to do so although I am very grateful for your
kind offer of the loan of your vacuum box I do not think I would know
how to use it and then do the figuring.

I have been told rightly or wrongly that the corrector plate is
matched to the primary on a test bench at the factory and that the
procedure requires an initial test which highlights any aberrations
and then the plate is re-figured and tested again until the right
match is achieved.

For me to duplicate this sounds a little to much for my skill level
as  my optical knowledge, as small as it is, has only been
accumulated since having to understand the problems with my scope.

If you are making a 10" cassegrain then I applaud you as it seems
that the majority of atm is involved with Newtonians, well done.

Dennis


--- In atm_free@yahoogroups.com, "ghb959" <ghberry@...> wrote:
>
>     Hi; Measure the diameter of your tube I have made a vaccuum box
> to do a 10 inch corrector plate. Email me if you want to borrow it.
> Newport Glass carry the glass and you can have them cut it to the
> correct diameter for your tube. Gordon
>
> --- In atm_free@yahoogroups.com, "nddxc06" <nddxc06@> wrote:
> >
> >  Celestron conversion
> >
> > ------------------------------------------------------------------
--
> --
> > ----------
> >
> > Hi,
> >
> > This is my first post here and I will unashamedly admit I am
> seeking
> > advice and what better repository of knowledge could there be
then
> > among the ATM community.
> >
> > Due to an unhappy accident my beloved Celestron 9.25 has been
left
> > devoid of a corrector plate and have deen advised to throw what
is
> > left away, considering that the primary and secondary mirrors are
> in
> > perfect condition I feel loath to do this.
> >
> > My thoughts turned to examples turned out from manufacturers such
> as
> > Tal, Vixen and Orion Optics that produce sub aperture designs
that
> > utilise spherical aberration correction components either in
front
> of
> > the secondary or further down the optical train.
> >
> > Curiosity has led me to fabricating a secondary spider just to
see
> > with my own eyes just how much spherical aberration is present
> > without the schmidt plate. (not completed yet), but my problem is
> how
> > would you determine the prescription for say a meniscus lens
placed
> > in front of the secondary or a doublet or triplet set at the exit
> > pupil.
> >
> > My reasoning is that these components are smaller and easier to
> > manufacture then a full aperture aspheriser's so may lead to a
more
> > econonomic adaptation for a useful life of the remains.
> >
> > The ideal scenario of course would be if I could make use of off
> the
> > shelf elements as that would contribute to the notion of economic
> > repair although without the specifications aquisition or
> manufacture
> > is academic.
> >
> > So the sticking point seems to be how to calculate what is
needed,
> > any suggestions would be happily received.
> >
>

My 8" F10 Mak-Cass, made by the late Max Bray, used a ribbed blank
from the discontinued Celestron 10" Schmidt-Cass/camera as the
primary. The 10" blank was then Blanchard ground to fit the smaller
diameter 9" primary. Max then ground and figured a BK7 mak corrector
with the third curve secondary ground and polished as an integral
part of the corrector. It was this Max Bray 8" Mak-Cass that my
prototype compliant moving mirror focuser was built for.

Don Clement
Running Springs, California



--- In atm_free@yahoogroups.com, "nddxc06" <nddxc06@...> wrote:
>
>  Celestron conversion
>
> --------------------------------------------------------------------
--
> ----------
>
> Hi,
>
> This is my first post here and I will unashamedly admit I am
seeking
> advice and what better repository of knowledge could there be then
> among the ATM community.
>
> Due to an unhappy accident my beloved Celestron 9.25 has been left
> devoid of a corrector plate and have deen advised to throw what is
> left away, considering that the primary and secondary mirrors are
in
> perfect condition I feel loath to do this.
>
> My thoughts turned to examples turned out from manufacturers such
as
> Tal, Vixen and Orion Optics that produce sub aperture designs that
> utilise spherical aberration correction components either in front
of
> the secondary or further down the optical train.
>
> Curiosity has led me to fabricating a secondary spider just to see
> with my own eyes just how much spherical aberration is present
> without the schmidt plate. (not completed yet), but my problem is
how
> would you determine the prescription for say a meniscus lens placed
> in front of the secondary or a doublet or triplet set at the exit
> pupil.
>
> My reasoning is that these components are smaller and easier to
> manufacture then a full aperture aspheriser's so may lead to a more
> econonomic adaptation for a useful life of the remains.
>
> The ideal scenario of course would be if I could make use of off
the
> shelf elements as that would contribute to the notion of economic
> repair although without the specifications aquisition or
manufacture
> is academic.
>
> So the sticking point seems to be how to calculate what is needed,
> any suggestions would be happily received.
>

Hi Don,

An 8" Mak sounds a great idea and my apoligies for not having heard
of Max Bray as he sounds like a very clever guy it is a shame he is
no longer with us.

It does prove one thing though, given the skills and motivation it
seems that good scopes can be made with recycled parts.

I hope you enjoy your scope Don and thanks for the reply.

Dennis



--- In atm_free@yahoogroups.com, "Donald Clement"
<donald_clement@...> wrote:
>
> My 8" F10 Mak-Cass, made by the late Max Bray, used a ribbed blank
> from the discontinued Celestron 10" Schmidt-Cass/camera as the
> primary. The 10" blank was then Blanchard ground to fit the smaller
> diameter 9" primary. Max then ground and figured a BK7 mak
corrector
> with the third curve secondary ground and polished as an integral
> part of the corrector. It was this Max Bray 8" Mak-Cass that my
> prototype compliant moving mirror focuser was built for.
>
> Don Clement
> Running Springs, California
>
>
>
> --- In atm_free@yahoogroups.com, "nddxc06" <nddxc06@> wrote:
> >
> >  Celestron conversion
> >
> > ------------------------------------------------------------------
--
> --
> > ----------
> >
> > Hi,
> >
> > This is my first post here and I will unashamedly admit I am
> seeking
> > advice and what better repository of knowledge could there be
then
> > among the ATM community.
> >
> > Due to an unhappy accident my beloved Celestron 9.25 has been
left
> > devoid of a corrector plate and have deen advised to throw what
is
> > left away, considering that the primary and secondary mirrors are
> in
> > perfect condition I feel loath to do this.
> >
> > My thoughts turned to examples turned out from manufacturers such
> as
> > Tal, Vixen and Orion Optics that produce sub aperture designs
that
> > utilise spherical aberration correction components either in
front
> of
> > the secondary or further down the optical train.
> >
> > Curiosity has led me to fabricating a secondary spider just to
see
> > with my own eyes just how much spherical aberration is present
> > without the schmidt plate. (not completed yet), but my problem is
> how
> > would you determine the prescription for say a meniscus lens
placed
> > in front of the secondary or a doublet or triplet set at the exit
> > pupil.
> >
> > My reasoning is that these components are smaller and easier to
> > manufacture then a full aperture aspheriser's so may lead to a
more
> > econonomic adaptation for a useful life of the remains.
> >
> > The ideal scenario of course would be if I could make use of off
> the
> > shelf elements as that would contribute to the notion of economic
> > repair although without the specifications aquisition or
> manufacture
> > is academic.
> >
> > So the sticking point seems to be how to calculate what is
needed,
> > any suggestions would be happily received.
> >
>

i have a celestron computerized NexStar102SLT that needs to have the
remote control firmware reflashed. does anyone know the pinout of the
modular (motor end) plug? (im using a USB to phone plug cable)..... $30
for a wire is way too much when i have everything to make one.

Thanks
John

Hi Mel,

This is interesting. I don't have Schroeder's but I think I have enough info
from your description to ray trace that.

On corrected DK's I've been playing mostly with a larger 16" designs. The
F/16 version has a diffraction limited field diameter of 0.75 deg. which far
exceeds what you would need to cover even a large format CCD like an SBIG
11000 ( 24 x 36mm).

Tony
BigEye Optics



----- Original Message -----
From: "Mel Bartels" <mbartels@...>
To: <atm_free@yahoogroups.com>
Sent: Monday, January 05, 2009 10:03 PM
Subject: RE: [atm_free] Re: ATM Cassegrain?


>>>>
> To my mind, the most interesting DK designs are the type that use a two
> element corrector group near focus. Some of these can deliver large
> diffraction limited fields at reasonable focal ratios.
> <<<
>
>
> Another idea that intrigues me is the 4 mirror design.  Two large mirrors
> which can be both spherical (or both parabolic) act to produce a parallel
> beam of light that is then imaged by two more mirrors, with the correction
> dumped (~12x over corrected) into the 3rd much smaller mirror (4th mirror
> is
> smallest yet).  The whole design can be quite fast and quite compact
> (think
> of the mirrors sitting in the edges of a box).  See Schroeder's
> Astronomical
> Optics, the chapter on 4 mirror designs.
>
> Mel Bartels
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>


--------------------------------------------------------------------------------



No virus found in this incoming message.
Checked by AVG - http://www.avg.com
Version: 8.0.176 / Virus Database: 270.10.3/1878 - Release Date: 1/6/2009
7:56 AM

Tony Gondola wrote:
> Hi Mel,
>
> This is interesting. I don't have Schroeder's but I think I have enough info
> from your description to ray trace that.
>
> On corrected DK's I've been playing mostly with a larger 16" designs. The
> F/16 version has a diffraction limited field diameter of 0.75 deg. which far
> exceeds what you would need to cover even a large format CCD like an SBIG
> 11000 ( 24 x 36mm).
>
> Tony
> BigEye Optics
>

Indeed.  It's sometimes amazing (to me, anyway) what a couple
of simple refractive elements can do.  Here is a corrected DK
(well, the conic had to be modified a bit) 16" f/10, flat
spectrum (395-1035 nm) diffraction limited over the field (about
0.47 degrees):

Title: rc7-02x
Corrected Dall-Kirkham Cassegrain

Surf     Radius  Thickness     Glass   Diameter    Conic

    1   Infinity       1050                516.7        0
STO   Infinity      11.16                  508        0
    3  -2892.035  -1036.802    MIRROR        508   -0.725
    4  -1152.982   1024.199    MIRROR      152.4        0
    5   Infinity       12.5     N-BK7         80        0
    6   -324.629        0.1                   80        0
    7   197.3163        5.5     N-BK7         80        0
    8   118.2409   375.4574                   80        0
IMA   Infinity                              42        0

Richard F.L.R. Snashall wrote:
> Indeed.  It's sometimes amazing (to me, anyway) what a couple
> of simple refractive elements can do.  Here is a corrected DK
> (well, the conic had to be modified a bit) 16" f/10, flat
>
Reconnect my brain long enough to call that 20" f/10...