Hi,

Welcome to my group.  It was created to have a place to discuss topics
that weren't quite at home in other places, like really fast mirrors.

I'll check the group as often as I can, but I spend a lot of time in
my shop and I'm not always online.

   Mike Lockwood
   Lockwood Custom Optics

--- In zambutomirrorgroup@yahoogroups.com, Paul Leuba <ngc891@...> wrote:
> This is what I would like to know as well...  I use a ParaCorr for
> low power deep sky in a SM 14.5 ZOC F/4.3.  At what point
> (F-ratio) does coma become so intrusive that even a PowerCor is of
> dubious use...  In other words, how low can you go?

That's what I'm trying to find out.  F/3 is OK for deep sky, I haven't
tried serious planetary yet.

I am thinking about trying a 14.5" F/2.6-2.7 for another experiment.

>  I don't much
> care for the views at F/4.3 without the ParaCorr - and I use all
> well corrected eyepieces - Nagler T4's, T5's and T6's.  Ancillary
> to this is that for high power planetary, I remove the ParaCorr
> because the ParaCorr does add some Spherical Aberration to the
> image.

Yes, a good point - most people don't realize that.

> At F/3, the diffraction limited area in the precise center of the
> optic is so tiny that  breathing upwind of the uppercage will be
> enough flex the structure to affect collimation - just kidding!!!
>   But, I think you get the picture.  For deep sky, I doubt it will
> be noticed.  Planetary, and double stars, on the other hand, will
> be problematic if collimation drifts around.  And really, if the
> optician fabricates the mirror a high standard (much better then
> diffraction-limited) it would be a shame if the telescope as a
> system was "collimation limited".   Sure precise collimation can
> be had, but its doubtful in an environ with falling temps and
> vigorous object-to-object slews, that collimation will be
> maintained with any sort of regularity.

That's a superb summary of the issues involved.

I didn't seen any collimation drift during my one night of observing
with it, all over the sky.  I'm still learning what the scope will do,
and I will learn more soon.  I intend to address those issues.

> My ZOC 14.5 SM goto/track has been the absolute best investment
> I've made in 32 years in the hobby.

It's a great combo - excellent optics and a nice size.

> Perhaps I am biased, but I am
> not a big fan of utra-fast, big aperture glass.  At the end of the
> day, I think the opticians will need to balance the market demand
> for F/3 glass with the ability of the "telescope-as-a-system"  to
> display diffraction limited views.  It would be a shame these F/3
> scopes to be relegated highend light bucket status.

Agreed, but I think diffraction limited is certainly doable, and I
will be the first one to demand that, being a picky observer.  I just
wish the atmosphere would cooperate!

What I saw last Saturday night impressed me, though, despite obviously
poor seeing conditions, and that is not easy to do.

What is more interesting is that it impressed THREE other serious,
experienced observers, too.

F/3 has other interesting advantages, such as for Mallincam and
Stellacam users (shorter exposure times) and for people who have
issues climbing ladders.

The 20" F/3 has certainly made my observing a lot more fun,
interesting, and comfortable lately (seated observing, no ladder).

   Mike Lockwood
   Lockwood Custom Optics

Hey Mike,

I rebuilt the focuser and moved the mirrors even closer.  I even got
the autofocuser working so now can focus perfectly every time.  I may
have moved the mirrors a little to close as the wagon wheels are back.
  I will see. check out the latest images from last night in the images
section.  With the moon up there is not much to image that is not
washed out.  Still trying to get a rochi image but it was just to cold
last night to be swapping out cameras and such.

Drew

I believe I had the chance to look through one of your mirrors last
year.

It was a 24" StarMaster that was shipped to California. Rick had it out
testing it at the Kansas groups dark sky site. The optics were great, I
liked the short stature of the scope , I have a 24" f4.2, and I would
not trade it for the world, but it takes an 8" ladder.

Are you located in central IL?

I'm in Bloomington and may have to make a trip to your shop sometime.

This is a group that I will monitor, because if I ever get a larger
scope , it would have the super fast optics in it.

Dan

Dan,

--- In lockwood_optics@yahoogroups.com, "bigdob24" <dsm@...> wrote:
> I believe I had the chance to look through one of your mirrors last
> year. It was a 24" StarMaster that was shipped to California. Rick
> had it out testing it at the Kansas groups dark sky site. The
> optics were great, I liked the short stature of the scope,

Thanks for the feedback.  Those 24"s are a really convenient size and
don't require a ladder, just a good three-step stool.

> I have a 24" f4.2, and I would
> not trade it for the world, but it takes an 8' ladder.

Ah, you're Dan from Bloomington with the 24" SM.  I looked through
your telescope at Astrofest a number of few years ago.  It is a fine
instrument.

> Are you located in central IL?

Yes, I live in Champaign, and I'm in the Bloomington area fairly
frequently.

> This is a group that I will monitor, because if I ever
> get a larger scope, it would have the super fast optics in it.

If you've been watching the Starmaster group, you may have seen that I
will be making a 30" F/3.3 later this year.  Not sure if that
interests you or not, but I thought I'd mention it.

Here are some general news items for everyone:
---------------------------------------------
Rick is now offering a 22" F/3.3 telescope as a standard model, and I
have started on a mirror for the first one.

I will make 20"-30" mirrors faster than F/3.7 for Starmaster
Telescopes, and Rick will build them (as with the 30" F/3.3 mentioned
above).  These are custom telescopes, and they are priced
appropriately.  Contact Rick if you are interested.

While I have glass in stock for standard sizes/focal ratios and
sources for large Pyrex blanks right now, I don't know how long they
will last.  I expect large blanks to be available in the future from
Pyrex substitutes/equivalents and cellular Pyrex/borosilicate (and
some smaller blanks in quartz), but prices of all of those will almost
surely be higher than good old sheet Pyrex.

So, if you're contemplating a 20"-40" Pyrex mirror in the future from
me, or if you are considering a large Starmaster telescope, then
starting your project sooner rather than later will probably save you
some money.

I will remain exclusive with Rick on 16"-30" f/3.7 mirrors, and on the
22" F/3.3.  Other sizes/focal ratios are non-exclusive.

Call Rick for Starmaster inquiries.  Email me for custom mirror inquiries.

   Mike Lockwood
   Lockwood Custom Optics

Last year at Mid South Star gaze at Rainwater observatory, MS, I met
Rick Singmaster for the first time.  He was there delivering the first
Lockwood FX 16.5 f/3.6.  I had my trusty and much loved 14.5 SM ZO,
and got to compare views.  Until that time I had thought the 14.5 was
the perfect scope for convenience, transportability, etc.  The 16.5"
changed my mind.  I also had my Teleket 25 inch f/4 Swazey there,
which is very heavy, needs a trailer to transport, and was getting a
bit too much for me to handle.

I had been thinking about getting another large scope that would be
bigger than the 14.5 but easier to handle than the 25, both of which
are now for sale.  Rick told me about Mike, and how they had met and
decided to experiment -- to push the envelope, as it were, with faster
optics.  Rick told me he had been looking for the right partner for a
long time.  He was convinced the old saws about faster mirrors having
excess coma, lack of flat field and being poor for planetary
observations were just plain wrong.  Together, they have proved this
to be so, at least up to a certain point, which they keep pushing.
Three years ago I was told an f4 was pushing it, then I saw the f3.6
FX 16.5" and the f/3.7 28" Starmasters that John had there at Mid
South.  It convinced me to put down a deposit for the first FX20 inch,
f 3.7.

It is a magnificent scope.  Rick delivered it to Chiefland Astronomy
Village and I was able to observe with him for several days under dark
skies with the moon waxing, sigh.  I belong to the Ponchartrain
Astronomy Society in New Orleans and I have posted a pic of me with
the scope at our dark sky site.

I agonized over what size scope to order.  I didn't want to go too far
below the 25" I owned and hoped to sell.  It was between a 20 and a 22
inch.  The deciding factor was the weight of the mirror and the
dimensions.  It had to be transportable in my Escalade.  No more
trailers for weekend travel to our site!  I was tired of step stools.
  The new scope had to be fast and short!  I often store my scope
assembled in the house, and it had to be able to go through a standard
36" door with the wheelbarrow handles.  The choice was made.  I really
wanted the 22", but only the 20" met the criteria. I am 5' 11", and at
the zenith only have to be 9" up! In the photo section I have posted
some photos of how I transport the scope.

The FX20 has turned out to be everything I had wished for.  It has
been judged as, "the best scope in the club", which, of course is
subjective, but the PAS is 50 years old this year and has a lot of
veteran accomplished observers far more capable of judging than me.

Well, as fate would have it, if I had waited I could have had the
larger 22".  Rick and Mike have gone ahead and pushed the envelope
some more and are offering a 22" f3.3, which will be in virtually the
same rocker and mirror boxes as the 20"! Same size, probably a lighter
mirror, and even shorter than the 20".  What a dream scope that will
be!  Maybe I will trade up someday, but I am still being amazed by the
brilliant images the 20 is affording me and all my fellow club members
who observe at our club site.

Dark, clear skies all,
Gary

Hi Mike!
    Here's a better way to use an f/3 primary. I uploaded a file for a
20 inch F/5 using a coma corrector on a f/3 primary. I could kick
myself for not taking home the special glass needed for this design
that they were throwing away at work.

Ed Jones

Ed,

Interesting.

What is the diameter of the lenses?
Does it require an uncommon type of glass?
How many Paracorrs would it cost?

   Mike Lockwood

--- In lockwood_optics@yahoogroups.com, "Ed Jones" <ejones@...> wrote:
>    Here's a better way to use an f/3 primary. I uploaded a file for a
> 20 inch F/5 using a coma corrector on a f/3 primary. I could kick
> myself for not taking home the special glass needed for this design
> that they were throwing away at work.
> Ed Jones

Hello Mike, hello group,

Thanks for the invitation! For now I do not have a telescope with
Mike's optics in it, but I can't wait for it to be the case!
The thing is that I am trying to make a bino-dob with Mike's optics
and that is a more demanding task the two separate dobs.

Anyway I will keep you updated with my progresses :-)

Hugues
Luxembourg, Europe


> Welcome to my group.  It was created to have a place to discuss topics
> that weren't quite at home in other places, like really fast mirrors.
>

Hi Mike,

<What is the diameter of the lenses? > 4.25 and 3.8 inches
<Does it require an uncommon type of glass?> ye one is
<How many Paracorrs would it cost?> I don't know what a Paracorr
costs or how much this glass costs but I would guess the blank would
cost less. I need to do a patent search to see if this has been done
before.

Ed


--- In lockwood_optics@yahoogroups.com, "Mike Lockwood"
<parabola30@...> wrote:
>
> Ed,
>
> Interesting.
>
> What is the diameter of the lenses?
> Does it require an uncommon type of glass?
> How many Paracorrs would it cost?
>
>   Mike Lockwood
>
> --- In lockwood_optics@yahoogroups.com, "Ed Jones" <ejones@> wrote:
> >    Here's a better way to use an f/3 primary. I uploaded a file
for a
> > 20 inch F/5 using a coma corrector on a f/3 primary. I could
kick
> > myself for not taking home the special glass needed for this
design
> > that they were throwing away at work.
> > Ed Jones
>

Is the prescription available for this?
The pdf showed the performance, but not the prescription.

Thanks,
Scott Beard

--- In lockwood_optics@yahoogroups.com, "Ed Jones" <ejones@...> wrote:
>
> Hi Mike!
>    Here's a better way to use an f/3 primary. I uploaded a file for a
> 20 inch F/5 using a coma corrector on a f/3 primary. I could kick
> myself for not taking home the special glass needed for this design
> that they were throwing away at work.
>
> Ed Jones
>

Ed,

Why not just develop an optimized coma corrector to go in a 2" or 3"
focuser for use at or near F/3?

That solution would be less expensive, it is not an integral part of
the instrument and thus could be moved from telescope to telescope.

If anyone on this group can suggest sources for coma correctors that
perform better than the Paracorr at F/3 and are practical to use with
eyepieces like Naglers and Ethos, I would like to hear about it.  It
will be difficult to beat the Paracorr for the price.

The 3" Keller correctors are fairly difficult to get and are
expensive.  What else is there?

   Mike Lockwood

Ed probably has some better explanation about the corrector, but from
what I know...

The further downstream you go (closer to the eyepiece), the harder it
is to get good correction. (Which is why the Parracor is a 6 element
corrector, rather than a 2 element, like Ed is showing.)

Also, if the corrector is built into the scope, you don't need
the "twist adjustement" that the paracorr has, that needs to be
adjusted for each type of eyepiece.  If your corrector moves with the
eyepiece, you need to be able to adjust for the fact that not all
eyepieces have their focal plane at the same distance from the
eyepiece "shoulder".  Fixing it to the secondary mirror solves that
problem.

Scott Beard

--- In lockwood_optics@yahoogroups.com, "Mike Lockwood"
<parabola30@...> wrote:
>
> Ed,
>
> Why not just develop an optimized coma corrector to go in a 2" or 3"
> focuser for use at or near F/3?
>
> That solution would be less expensive, it is not an integral part of
> the instrument and thus could be moved from telescope to telescope.
>
> If anyone on this group can suggest sources for coma correctors that
> perform better than the Paracorr at F/3 and are practical to use
with
> eyepieces like Naglers and Ethos, I would like to hear about it.  It
> will be difficult to beat the Paracorr for the price.
>
> The 3" Keller correctors are fairly difficult to get and are
> expensive.  What else is there?
>
>   Mike Lockwood
>

Scott,

--- In lockwood_optics@yahoogroups.com, "scott_beard2000"
<indianola@...> wrote:
> The further downstream you go (closer to the eyepiece), the harder
> it is to get good correction. (Which is why the Parracor is a 6
> element corrector, rather than a 2 element, like Ed is showing.)

Right, but the Paracorr does a fairly good job as is.  I wonder how it
would do if its design was optimized for F/3 rather than F/4.5.

It is a 4-element corrector (two doublets) according to the TeleVue
site, by the way:
   http://www.televue.com/engine/page.asp?ID=56

> If your corrector moves with the eyepiece, you need to be able to
> adjust for the fact that not all eyepieces have their focal plane
> at the same distance from the eyepiece "shoulder".

Good point.

However, 4" lens elements are not inexpensive, and to make one of
these for a 30" F/3 would mean closer to 6" lenses.  The design also
increases the focal ratio, which imagers and some visual observers
will not find desirable because it increases exposure time and reduces
the field of view.

So, while it might be suitable for use in smaller scopes or telescopes
used for wide-field imaging, I do not think its cost can be justified
for visual use.

Has anyone used a non-Paracorr corrector visually?

   Mike Lockwood

It makes an intersting question.

As you correct more coma, you create more spherical abberation. This
is why the parracor has some residual spherical abberation. You can't
get rid of it, but you can reduce it by either adding more lenses, or
moving the assembly 'upstream'.

Whether in correcting for the greater coma of an F3, the larger
residual SA gets too bad, or whether it pushes you into a 6-element
design, I don't know.  (You are also fighting astigmatism, which also
gets better with either more elements, or moving upstream.)Someone
would have to give it a try.

It is certainly an intersting idea. With more F3's likely to come on
line, there will be a market for someone who answers that question.

Regarding simpler 2-element correctors at the focuser-
I read several reviews of some less expensive comma correctors, prior
to buying my parracor. The reviews at that time all stated that the
non-parracor correctors were only for photographic work. They weren't
good enough for visual.

At the time, the alternates were all 2-element. Photo only for a 2
element at focuser is what I would have expected.

(sorry for the miss-statement about 6 elements. I read an article
years ago, when they were first developing it. At that time they were
anticipating a 6 element.  That incorrect factoid keeps popping up in
my memory, when I'm not paying close enough attention.)

Scott Beard


--- In lockwood_optics@yahoogroups.com, "Mike Lockwood"
<parabola30@...> wrote:
>
> Scott,
>
> --- In lockwood_optics@yahoogroups.com, "scott_beard2000"
> <indianola@> wrote:
> > The further downstream you go (closer to the eyepiece), the
harder
> > it is to get good correction. (Which is why the Parracor is a 6
> > element corrector, rather than a 2 element, like Ed is showing.)
>
> Right, but the Paracorr does a fairly good job as is.  I wonder how
it
> would do if its design was optimized for F/3 rather than F/4.5.
>
> It is a 4-element corrector (two doublets) according to the TeleVue
> site, by the way:
>   http://www.televue.com/engine/page.asp?ID=56
>
> > If your corrector moves with the eyepiece, you need to be able to
> > adjust for the fact that not all eyepieces have their focal plane
> > at the same distance from the eyepiece "shoulder".
>
> Good point.
>
> However, 4" lens elements are not inexpensive, and to make one of
> these for a 30" F/3 would mean closer to 6" lenses.  The design also
> increases the focal ratio, which imagers and some visual observers
> will not find desirable because it increases exposure time and
reduces
> the field of view.
>
> So, while it might be suitable for use in smaller scopes or
telescopes
> used for wide-field imaging, I do not think its cost can be
justified
> for visual use.
>
> Has anyone used a non-Paracorr corrector visually?
>
>   Mike Lockwood
>

Mike,
   <<Why not just develop an optimized coma corrector to go in a 2"
or 3"  focuser for use at or near F/3?>>
Actually exploring that option I found a Paracorr "like" solution
that uses common glass.  It would interesting to compare it a
Paracorr but I don't have the prescription. I guess the only
criticism is that it would need a bigger flat, over 5 inches.

Ed

--- In lockwood_optics@yahoogroups.com, "Mike Lockwood"
<parabola30@...> wrote:
>
> Ed,
>
> Why not just develop an optimized coma corrector to go in a 2" or
3"
> focuser for use at or near F/3?
>
> That solution would be less expensive, it is not an integral part
of
> the instrument and thus could be moved from telescope to telescope.
>
> If anyone on this group can suggest sources for coma correctors
that
> perform better than the Paracorr at F/3 and are practical to use
with
> eyepieces like Naglers and Ethos, I would like to hear about it.
It
> will be difficult to beat the Paracorr for the price.
>
> The 3" Keller correctors are fairly difficult to get and are
> expensive.  What else is there?
>
>   Mike Lockwood
>

I uploaded a file on a Paracorr "like" coma corrector that I designed
in about 5 minutes for a 20 inch F/3 primary. The doublets are SF2/BK7
pairs about 1.4 inches in diameter and 2 inches from focus. I have no
idea what the real Paracorr is but one could be made to work. Final F#
is 3.8.

Ed Jones

Greetings all,

I'll post this in full tomorrow and on the ATM list after I get my
notes together...

Last fall I had an interesting lengthy discussion with Al Nagler about
what Tele Vue could do for very fast mirrors - as the converging trend
lines of thin/fast/light coupled with new design on supporting
structures meant one didn't have to be too psychic to spot the last
piece needed for a killer commercial product.

To cut to the chase, Al's very interested in building small qty runs
of a new prototype ParaCorr with improved SA correction and suited for
f/3-4 application, most likely by adding an extra element to the
current production model.  Ya gotta love that!

Best,
Mark Cowan

--- In lockwood_optics@yahoogroups.com, eric charl <ericcharl@...>
wrote:
>
> Hi,
>  
> i have founded some prescriptions here:
>  
> http://www.jeandijon.com/correcteurs_de_champ_pour_miroir.htm
>  
> Lot's of different design are proposed and analysed.
> It is a french vvebsite.
>  
> Do you think it can help you ?


Very usefull.I recall an article in the TM series of a off the self
home made coma corrector from stock lenses.

Ric
>

Hi Everyone;
     In Telescope Making # 45 page 30 thru 33. There is a article on
How To Make A Coma Corrector with Off-the-shelf Optics.
     I made a PDF file, but could not upload to the site. Anyone that
does not have the article I could try to email it or regular mail.
Gordon

--- In lockwood_optics@yahoogroups.com, "Ric Rokosz" <radicell2@...>
wrote:
>
> --- In lockwood_optics@yahoogroups.com, eric charl <ericcharl@>
> wrote:
> >
> > Hi,
> >  
> > i have founded some prescriptions here:
> >  
> > http://www.jeandijon.com/correcteurs_de_champ_pour_miroir.htm
> >  
> > Lot's of different design are proposed and analysed.
> > It is a french vvebsite.
> >  
> > Do you think it can help you ?
>
>
> Very usefull.I recall an article in the TM series of a off the self
> home made coma corrector from stock lenses.
>
> Ric
> >
>

Hi,

--- In lockwood_optics@yahoogroups.com, "Aurigema, Andrew N.
(KSC)[ASRC AEROSPACE]" <andrew.n.aurigema@...> wrote:
> did you try to put it in the " FILES " section.  I would like to
> see it.

That's copyrighted material, so it's not legal to post reproductions
of it in the files section or any other section here.

Thankfully some of the TM issues (long out of print) are beginning to
be offered electronically by Kalmbach.

I'm going to try to talk to Al Nagler about the Paracorr again.  I
told him about my F/3 project a few months ago.  I'm not sure if he'll
be at WSP to see it.

FYI, we generated a 14.5" F/2.6 mirror that I hope to work on later
this year.  That will be my new RFT, which stands for both "rich-field
telescope" and "really fast telescope".

   Mike Lockwood
   Lockwood Custom Optics

Hi,

--- In zambutomirrorgroup@yahoogroups.com, "Michael Gilbreath"
<MichaelGilbreath@...> wrote:
> As you undoubtedly know Al designed the Paracorr for use at about
> f/4.5. With a very small market at f/3 it would seem doubtful he
> would manufacture anything for use at this F-ratio.

When it came out, the Paracorr was very appropriate for the market and
matched the focal ratio range that needed it.

But now the imaging and visual market below F/4 is growing, and I
suspect a tweak of the design wouldn't be that difficult.

I've talked to Al about my F/3 project.  He seemed interested.

   Mike Lockwood
   Lockwood Custom Optics

Hi,

IN CASE you didn't see my warning in my previous message, posting
copyrighted material is illegal and I won't allow it here.  I removed
the message and the files.

Future posting or encouragement to post copyrighted materials will
cause me to delete messages and files or take other action.  I would
rather spend my time making mirrors than playing group policeman.

Here is a link to the back issues that are currently offered by the
former publisher of Telescope Making magazine:

http://kalmbachcatalog.stores.yahoo.net/astronomy-telescope-making-downloadable-\
issues.html

Hopefully they'll get all of the issues up there at some point.

   Mike Lockwood
   Lockwood Custom Optics

Hi Mike; Sorry about the posting it will not happen again. Just
trying to help the cause. Gordon

--- In lockwood_optics@yahoogroups.com, "Mike Lockwood"
<parabola30@...> wrote:
>
> Hi,
>
> IN CASE you didn't see my warning in my previous message, posting
> copyrighted material is illegal and I won't allow it here.  I
removed
> the message and the files.
>
> Future posting or encouragement to post copyrighted materials will
> cause me to delete messages and files or take other action.  I would
> rather spend my time making mirrors than playing group policeman.
>
> Here is a link to the back issues that are currently offered by the
> former publisher of Telescope Making magazine:
>
> http://kalmbachcatalog.stores.yahoo.net/astronomy-telescope-making-
downloadable-issues.html
>
> Hopefully they'll get all of the issues up there at some point.
>
>   Mike Lockwood
>   Lockwood Custom Optics
>

That would be great and I would for sure be interested if Al were to
do that.

Duane

--- In lockwood_optics@yahoogroups.com, "Mark Cowan" <toolontop@...>
wrote:
>
> Greetings all,
>
> I'll post this in full tomorrow and on the ATM list after I get my
> notes together...
>
> Last fall I had an interesting lengthy discussion with Al Nagler about
> what Tele Vue could do for very fast mirrors - as the converging trend
> lines of thin/fast/light coupled with new design on supporting
> structures meant one didn't have to be too psychic to spot the last
> piece needed for a killer commercial product.
>
> To cut to the chase, Al's very interested in building small qty runs
> of a new prototype ParaCorr with improved SA correction and suited for
> f/3-4 application, most likely by adding an extra element to the
> current production model.  Ya gotta love that!
>
> Best,
> Mark Cowan
>

WHY NOT?- simply because the closer you approach the focal point
of the main mirror, the more wicked the curves become to force the
correction in the shorter distance remaining, far more critical
spacing and collimation requirements, etc. Ed can correct me if I'm
wrong, but it's generally the case in any multi-element system.
    In retrospect, the closer you get to the focus of your fast
mirror, the more expensive it'll get!
Regards,  Mark
************************
--- In lockwood_optics@yahoogroups.com, "Mike Lockwood"
<parabola30@...> wrote:
>
> Ed,
>
> Why not just develop an optimized coma corrector to go in a 2" or
3"
> focuser for use at or near F/3?
>
> That solution would be less expensive, it is not an integral part
of
> the instrument and thus could be moved from telescope to telescope.
>
> If anyone on this group can suggest sources for coma correctors
that
> perform better than the Paracorr at F/3 and are practical to use
with
> eyepieces like Naglers and Ethos, I would like to hear about it.
It
> will be difficult to beat the Paracorr for the price.
>
> The 3" Keller correctors are fairly difficult to get and are
> expensive.  What else is there?
>
>   Mike Lockwood
>

Ed, is the Paracorr "like" corrector in front of the secondary flat,
or in the focuser???
Mark
********

--- In lockwood_optics@yahoogroups.com, "Ed Jones" <ejones@...>
wrote:
>
> Mike,
>   <<Why not just develop an optimized coma corrector to go in a 2"
> or 3"  focuser for use at or near F/3?>>
> Actually exploring that option I found a Paracorr "like" solution
> that uses common glass.  It would interesting to compare it a
> Paracorr but I don't have the prescription. I guess the only
> criticism is that it would need a bigger flat, over 5 inches.
>
> Ed
>
> --- In lockwood_optics@yahoogroups.com, "Mike Lockwood"
> <parabola30@> wrote:
> >
> > Ed,
> >
> > Why not just develop an optimized coma corrector to go in a 2"
or
> 3"
> > focuser for use at or near F/3?
> >
> > That solution would be less expensive, it is not an integral
part
> of
> > the instrument and thus could be moved from telescope to
telescope.
> >
> > If anyone on this group can suggest sources for coma correctors
> that
> > perform better than the Paracorr at F/3 and are practical to use
> with
> > eyepieces like Naglers and Ethos, I would like to hear about
it.
> It
> > will be difficult to beat the Paracorr for the price.
> >
> > The 3" Keller correctors are fairly difficult to get and are
> > expensive.  What else is there?
> >
> >   Mike Lockwood
> >
>