--- In bigdob@yahoogroups.com, "Les Dalrymple" <lesdal@o...> wrote:
> Hi Bill & All,
>
> I tried to respond to you off list to you as the visibility of the
Pal clusters as it seems to get discussed pretty frequently on this
list, but the the email link off your web page won't work for me (Nice
web page BTW).  Here goes [excellent notes snipped]

Les, Thanks for posting your notes. I've saved them to my computer for
future reference and look forward to tackling more of these
challenging globulars over the next year or so.

Bill in Flagstaff

Try "Newt" (freeware) at
<http://home.att.net/~dale.keller/atm/newtonians/newtsoft/newtsoft.htm>

-John


--- Panoscanner <jordanka@...> wrote:

> Just finished an 18" AstroSystems Telekit.  Trying to optimize the scope for
> Denk II
> binoviewers.  Have shortened the tubes by 1.25" so the bino's will focus.
> Looks like I need to
> lose another .5" to be able to use the filter slide.  At this point none of
> my single eyepieces
> will focus but have a 2" focuser extension if I want to bo to cyclops mode.
> Starting to get
> concerned about losing light by moving the secondary closer to the primary
> and am thinking
> of going from a 3.1" diagonal to a 3.5" diagonal.  Haven't found any software
> programs to let
> me model the effect of moving the secondary closer to the primary and see the
> effects with a
> Ray trace.  Anybody have any ideas?  Thanks in advance.
>
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
>


__________________________________________________
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Paul, others:

The narrow-beam laser will show the aim of the focuser axis (reflected in
the secondary) on the primary, but the position of the returning beam is a
mixture (=vector sum) of the aiming errors of the focuser and primary axes.

The Cheshire, as well as the barlowed laser, shows the collimation of the
primary, independently (within reason) of the focuser axis - the B.L. might
have the advantage if you can look at the target at close range - depending
on the design of the focuser and upper tube assembly (the Cheshire will be
seen as if one f.l. away but the precision of reading is also influenced by
the size of the spot/donut). Thus, the Cheshire and B.L should agree, and
there is no obvious point in using the one to check the other.

The autocollimator shows a strange mixture of errors - it can be very
sensitive, but totally non-specific - it may show that collimation is off
even by a small amount, but won't give you a clue to what to adjust! You
will have to use it with a Cheshire or BL to set the primary collimation
right - this done, you can conclude that the remaining error, if any, is
that of the focuser axis.

Also you might consider that an error of the primary will show up as coma in
the center of the field, while miscollimation of the focuser axis can only
show up at the edge as defocusing - you can allow a pointing error of 1/30
of the primary diameter and still have the defocusing error very much less
than the unavoidable coma - i.e 1/2" on a 15" mirror! Using a coma
corrector, you should aim for 1/150 or so - 0.1" on that 15". You will
easily do it with an AC or laser beam - provided the focuser is good enough
not to sag under the load of the laser *or* the EP!

Just some thoughts.

Nils Olof


---- Original Message -----
From: "paul_winalski" <Prune@...>
To: <bigdob@yahoogroups.com>
Sent: Tuesday, August 30, 2005 2:57 AM
Subject: [bigdob] Re: how to collimate a tscope T14 or a big dob?


> --- In bigdob@yahoogroups.com, "Koehler, Steve" <steve_koehler@s...>
> wrote:
>>
>> Someone mentioned
>> checking the barlowed laser results with a Cheshire.  It's not a bad
> idea to
>> double check critical adjustments, but if one trusts the Cheshire
> more than the
>> laser, why not save time and just use the Cheshire?
>
> I was the one who made that remark.  I do trust the Cheshire more than
> the laser, but I find it much easier to make the adjustments using the
> laser than with the Cheshire.  So I use the laser for the adjustments
> themselves and the Cheshire as a last-minute double check.  If the
> double check still shows things are off a tad (and usually it
> doesn't), then I'll go through the (for me) more tedious process of
> adjusting the primary tilt using the Cheshire.
>
> -Paul W.
>
>
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
>

> Try "Newt" (freeware) at

Thanks for the tip.  Newt is a nice program though as far as I can determine,
there is no way
to change the secondary to primary distance parameter which is what is important
in this
case.  Maybe somebody can suggest a work-around to fool the program.

can we computed a follded newton  like this one maybe
http://johanneswilm.isasecret.com/mike/telescope/

it is a very new desing but interessting for big at f bigger then 8

jack 47'N 71'O



> Try "Newt" (freeware) at
> <http://home.att.net/~dale.keller/atm/newtonians/newtsoft/newtsoft.htm>
>
> -John
>
>
> --- Panoscanner <jordanka@s...> wrote:
>
> > Just finished an 18" AstroSystems Telekit.  Trying to optimize the
scope for
> > Denk II
> > binoviewers.  Have shortened the tubes by 1.25" so the bino's will
focus.
> > Looks like I need to
> > lose another .5" to be able to use the filter slide.  At this
point none of
> > my single eyepieces
> > will focus but have a 2" focuser extension if I want to bo to
cyclops mode.
> > Starting to get
> > concerned about losing light by moving the secondary closer to the
primary
> > and am thinking
> > of going from a 3.1" diagonal to a 3.5" diagonal.  Haven't found
any software
> > programs to let
> > me model the effect of moving the secondary closer to the primary
and see the
> > effects with a
> > Ray trace.  Anybody have any ideas?  Thanks in advance.
> >
> >
> >
> >
> >
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
> >
> >
>
>
> __________________________________________________
> Do You Yahoo!?
> Tired of spam?  Yahoo! Mail has the best spam protection around
> http://mail.yahoo.com

Paul,

> I was the one who made that remark.  I do trust the Cheshire more than
> the laser, but I find it much easier to make the adjustments using the
> laser than with the Cheshire.  So I use the laser for the adjustments
> themselves and the Cheshire as a last-minute double check.  If the
> double check still shows things are off a tad (and usually it
> doesn't), then I'll go through the (for me) more tedious process of
> adjusting the primary tilt using the Cheshire.

This makes sense.  You must be able to adjust the primary while at the
collimation screws, and not have to walk around to the front of the telescope.
Collimation got faster for me with the Cheshire when I noticed that one
collimation screw mostly moves the center spot up and down, while the other
collimation screw mostly moves the center spot left and right.  Now, if I can
only remember which direction to turn the screws!  Nevertheless, collimation
with the Cheshire never takes me more than about a minute.

-- Steve Koehler
    steve_koehler@...

The information contained in this email message may be privileged, confidential
and protected from disclosure. If you are not the intended recipient, any
review, dissemination, distribution or copying is strictly prohibited. If you
have received this email message in error, please notify the sender by reply
email and delete the message and any attachments.

That's a "dependent" variable in the program.  Set all the rest of the relevant
specs, and the tube length will be calculated for you.  Enter the aperture and
focal ratio (so the program knows the focal length), and then enter the spacing
from mirror face to tube rear, and focuser to tube front.  Then enter the
focuser height.  Finally, set the "spare focuser in travel" to a high enough
number to allow the binoviewer to reach focus.  Then click "accept" and the
tube length (and thus the sec to primary distance) will be adjusted to fit.

-John


--- Panoscanner <jordanka@...> wrote:

>
> > Try "Newt" (freeware) at
>
> Thanks for the tip.  Newt is a nice program though as far as I can determine,
> there is no way
> to change the secondary to primary distance parameter which is what is
> important in this
> case.  Maybe somebody can suggest a work-around to fool the program.
>
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
>
>


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around
http://mail.yahoo.com

--- In bigdob@yahoogroups.com, "Koehler, Steve" <steve_koehler@s...>
wrote:
> Paul,
>
> This makes sense.  You must be able to adjust the primary while at the
> collimation screws, and not have to walk around to the front of the
telescope.

Yes.  The narrow-beam laser collimator I have, the Orion Lasermate
Deluxe, has an observing hole cut in the side.  You can stand at the
back of the scope and tweak the collimation screws while watching the
beam.  You fiddle with the screws until the returning beam shines back
into the hole it's projected from.  This gets one very close to
perfect, without having to run back and forth between the eyepiece and
the bnck of the scope.  If the double check with the Cheshire still
shows some error, then I'll make those final few tweaks the hard way.

-Paul W.

> Yes.  The narrow-beam laser collimator I have, the Orion Lasermate
> Deluxe, has an observing hole cut in the side.  You can stand at the
> back of the scope and tweak the collimation screws while watching the
> beam.

Thanks, Paul.  It sounds like this is not a barlowed laser, then.

-- Steve Koehler
    steve_koehler@...

The information contained in this email message may be privileged, confidential
and protected from disclosure. If you are not the intended recipient, any
review, dissemination, distribution or copying is strictly prohibited. If you
have received this email message in error, please notify the sender by reply
email and delete the message and any attachments.

Steve,
one way is to put a sticker somewhere convenient near the focuser, drawing
two arrows on it indicating the direction that the spot (or the Cheshire
background) seems to move when you move either of the two collimating screws
inwards (or outwards - you decide and memorize which). With most setups the
directions will be at 60 degrees (or 120 if you prefer) to each other.

With some telescopes, at least, you may look down the mirror box and see the
reflection in the primary of the Barlowed laser via the secondary, while
reaching the collimation bolts. This would allow you to do all but perhaps
the last little tweak under visual control.... or even watch the reflection
magnified in one half of a binocular - it is focused at infinity.

Nils Olof

> This makes sense.  You must be able to adjust the primary while at the
> collimation screws, and not have to walk around to the front of the
> telescope.
> Collimation got faster for me with the Cheshire when I noticed that one
> collimation screw mostly moves the center spot up and down, while the
> other
> collimation screw mostly moves the center spot left and right.  Now, if I
> can
> only remember which direction to turn the screws!  Nevertheless,
> collimation
> with the Cheshire never takes me more than about a minute.

Nils Olof,

> one way is to put a sticker somewhere convenient near the focuser, drawing
> two arrows on it indicating the direction that the spot (or the Cheshire
> background) seems to move when you move either of the two collimating
> screws
> inwards (or outwards - you decide and memorize which).

Yes, I'm aware of this idea.  I just haven't implemented it, yet.  I have
attempted to remember without this aid, but one aspect that makes it confusing
is that clockwise on one screw moves the spot away from the center, but
clockwise on the other screw moves the spot toward the center.

> With most setups the
> directions will be at 60 degrees (or 120 if you prefer) to each other.

That's the case for me, too, but with the scope pointed at 45 degrees (which is
how I usually collimate), the two screws move the center spot approximately
horizontally and vertically.  At least, this makes it easy for me to remember
what they do.  I usually work by adjusting the right screw to put the center
spot at the same altitude as the Cheshire circle, then work the left screw to
move it side-to-side into place.  It usually takes another adjustment or two of
both screws to finish.

-- Steve Koehler
    steve_koehler@...

The information contained in this email message may be privileged, confidential
and protected from disclosure. If you are not the intended recipient, any
review, dissemination, distribution or copying is strictly prohibited. If you
have received this email message in error, please notify the sender by reply
email and delete the message and any attachments.

For the ultimate in aperture envy:
http://www.nytimes.com/2005/08/30/science/space/30mirr.html

hat tip to David Sheppard on the Obsession User group


Login info from bugmenot.com for those who don't want to subscribe to
the NY Times web site:
Account #1
jabloughme
yayaya

Dave
macaddicted

[Non-text portions of this message have been removed]

--- In bigdob@yahoogroups.com, "Gregg" <starryskyn@y...> wrote:
> Royce has issued a statement that conical backed mirrors will have
a
> central zone that is aluminized and contiguous with the rest of
> surface.  Center spot application for laser alignment should be no
> problem.
Gregg
I'm curious, where have you seen this stated? (I will to email him
for more details) Unfortunately, this solves one problem while
creating another. The ability to secure the mirror against a backing
plate by way of that central pref is lost. Trade-offs...
Joe

About 5 years ago our astronomy club had its 20" primary mirror recoated. This
mirror was homemade, but quite respectable. Unfortunately, it had a lot of chips
around the edge, mostly the result of carelessness. At any rate, Spectrum coated
it, and it does remarkably well, regardless of the chips. (They coated right
over the chips.)

We have one very large chip, the size of a silver dollar, and a dozen small
chips (1/4" diameter). All are on the edge of the mirror.

Now we are in the process of rebuilding the rest of the telescope, using the
original optics. But several of our members have asked if we would not get
better image contrast if we somehow masked the chips. Ordinary flat black paint
sounds good, just enough to cover each chip, especially the edges. That should
stop any reflections from irregular surfaces.

But does this pose a problem to a future recoat?  Not that the mirror needs
coating right now -- it doesn't. But who knows what will happen 5 or 10 years
from now?

If you have experience with such a condition, could give us some advice about
painting out the chips? What will work that won't jeopardize a later recoat?

Thanks

Bob Arr

http://www.latimes.com/travel/outdoors/la-os-
dobson30aug30,1,3411545.story?coll=la-headlines-
outdoors&ctrack=1&cset=true

http://www.rfroyce.com/conical/  --it is best to go to the source.
--- In bigdob@yahoogroups.com, "Joe Cannavo" <jpcannavo@y...> wrote:
> --- In bigdob@yahoogroups.com, "Gregg" <starryskyn@y...> wrote:
> > Royce has issued a statement that conical backed mirrors will have
> a
> > central zone that is aluminized and contiguous with the rest of
> > surface.  Center spot application for laser alignment should be no
> > problem.
> Gregg
> I'm curious, where have you seen this stated? (I will to email him
> for more details) Unfortunately, this solves one problem while
> creating another. The ability to secure the mirror against a backing
> plate by way of that central pref is lost. Trade-offs...
> Joe

Hi Bob,

I remember at our society we faced a similar problem with a 16" f6 mirror that
had a couple of edge chips over 1/2" diameter. We simply "coloured the chips in"
with a black permanent marker.  Seemoed to work well in use. No probs at all
when it had to be re-coated 7 years later it came off with a suitable solvent.

Cheers & Clear Skies,


Les D

The three laws of Thermodynamics (summarised)
1st Law:   "You can't win".
2nd Law:  "You can't break even"
3rd Law:   "You can't leave the game"
   ----- Original Message -----
   From: mrbobarr
   To: bigdob@yahoogroups.com
   Sent: Wednesday, August 31, 2005 6:28 AM
   Subject: [bigdob] Chipped mirror


   About 5 years ago our astronomy club had its 20" primary mirror recoated. This
mirror was homemade, but quite respectable. Unfortunately, it had a lot of chips
around the edge, mostly the result of carelessness. At any rate, Spectrum coated
it, and it does remarkably well, regardless of the chips. (They coated right
over the chips.)

   We have one very large chip, the size of a silver dollar, and a dozen small
chips (1/4" diameter). All are on the edge of the mirror.

   Now we are in the process of rebuilding the rest of the telescope, using the
original optics. But several of our members have asked if we would not get
better image contrast if we somehow masked the chips. Ordinary flat black paint
sounds good, just enough to cover each chip, especially the edges. That should
stop any reflections from irregular surfaces.

   But does this pose a problem to a future recoat?  Not that the mirror needs
coating right now -- it doesn't. But who knows what will happen 5 or 10 years
from now?

   If you have experience with such a condition, could give us some advice about
painting out the chips? What will work that won't jeopardize a later recoat?

   Thanks

   Bob Arr





   SPONSORED LINKS Astronomy telescope  Dobsonian telescope


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[Non-text portions of this message have been removed]

I believe there's some info on Royce's website that describes this.  The mirror
is still held by a single center bolt, but it's glued into a blind hole in the
back center of the mirror.

-John


--- Joe Cannavo <jpcannavo@...> wrote:

> --- In bigdob@yahoogroups.com, "Gregg" <starryskyn@y...> wrote:
> > Royce has issued a statement that conical backed mirrors will have
> a
> > central zone that is aluminized and contiguous with the rest of
> > surface.  Center spot application for laser alignment should be no
> > problem.
> Gregg
> I'm curious, where have you seen this stated? (I will to email him
> for more details) Unfortunately, this solves one problem while
> creating another. The ability to secure the mirror against a backing
> plate by way of that central pref is lost. Trade-offs...
> Joe
>
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
>


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around
http://mail.yahoo.com

Just completed the retro-fit drive system (ServoCat with Argo Navis) all
wireless hand controlled and wireless to the computer.  Since my 36" is
the largest and only 36" ever built by Starsplitter, I was certainly
apprehensive about the drive system being able to handle the monster.
  The scope is a f/5.1 so it reaches 19' when vertical.  However, the
ServoCat proved to be an easy match for that size scope.  It moved
errorlessly and seemingly effortlessly in both axes with virually no
sound.  Also, the go-to function was just simply "spot on".  I opted to
get the 10,000 tick encoders and my 36" is now more accurate than my 12"
Meade LX200 could ever imagine being even using the expert system and
accounting for drive gear errors.  I was too excited to let the scope
remain on any object too long, but we did stay on the Triffid going from
non-filter to filter for about 5 minutes, and there was no change of the
object position in the field of view. (ever see blues and reds in the
Triffid?)  In my case, we had to remove the previous drive system by
A.S. (don't want to be cruel), but what an amzing difference in ease of
movement, smothness and accuracy.  I feel like my scope has moved up in
it's ability to function as a serious scope by about 10 steps.  Should
add that the "spiral function" is simply ingenious.  With large dobs,
there are always some nearby smaller and dimmer fuzzies that are within
range of the scope.  A simple touch of a button and you search the area
out in a spiral pattern away from your object.  Stop when you notice
something and observe. Then  touch a button to return to the primary
object.  I just can't describe what a joy that feature adds to the scope
and the observing session.
      Besides the visual use of the scope, I do plan to experiment with
some video cams and feel confident that a new dimension has been added
to the scope in that regard, also.  Am I a happy camper!  You bet!
  Thanks to Gary of RX Design and the ServoCat, my 36" is now a
"complete" formidable instrument.  Anyone wishing to see the scope
"post" ServoCat, you can view it at
      http://c3po.cochise.edu/astro/observatories04.htm

--- In bigdob@yahoogroups.com, "Nils Olof Carlin" <nilsolof.carlin@t...> wrote:
> The autocollimator shows a strange mixture of errors - it can be very
> sensitive, but totally non-specific - it may show that collimation is off
> even by a small amount, but won't give you a clue to what to adjust!

In practice, when using the autocollimator, if you can see all four reflections
of the primary mirror center spot, you should use the "carefully decollimated
primary mirror" protocol. This protocol separates the reflections and allows
the user to first eliminate the focuser axial error and then systematically
zero the primary mirror axial error. As a final "proof" of accuracy, the
primary mirror axis can be confirmed with either a Cheshire eyepiece or
Barlowed laser.

On the other hand, if you can't see all four reflections, you can safely assume
that any remaining error visible in the autocollimator after using a Cheshire
eyepiece or Barlowed laser is the result of a focuser axial error (as Nils Olof
mentions in his post.) The important clue here is *not* to adjust the primary
mirror! Typically, the primary mirror center spot will be flanked on either side
by two reflections, the upright reflection appearing twice as close as the
apparently inverted reflection. (If the flanking reflections appear equidistant
from the primary mirror center spot, you need to reevaluate your Cheshire/
Barlowed laser collimation!) In the typical "iterative" protocol, either the
diagonal
or focuser is aligned to merge the reflections, then the process is reiterated
with the Cheshire/Barlowed laser, then back to the autocollimator, until both
tools show properly (axially) collimated optics.

Vic

No, the Lasermate Deluxe isn't a barlowed laser collimator.  But with
a barlow lens and a Kentrick 125-BLM or 2-BLM mask (or homemade
equivalent), you can turn it into one.  I've taken to using that
method to fine-tune the collimation after using the Lasermate in
narrow-beam mode.

Of course, when barlowed in this way, you don't have the convenience
of standing at the back of the scope while you adjust things--you have
to run back and forth between the UCA and the back.

-Paul W.


--- In bigdob@yahoogroups.com, "Koehler, Steve" <steve_koehler@s...>
wrote:
> > Yes.  The narrow-beam laser collimator I have, the Orion Lasermate
> > Deluxe, has an observing hole cut in the side.  You can stand at the
> > back of the scope and tweak the collimation screws while watching the
> > beam.
>
> Thanks, Paul.  It sounds like this is not a barlowed laser, then.

Maybe I missed it, but I didn't see anything about an aluminized
center spot on that page.

-Paul W.

--- In bigdob@yahoogroups.com, "Gregg" <starryskyn@y...> wrote:
> http://www.rfroyce.com/conical/  --it is best to go to the source.
> --- In bigdob@yahoogroups.com, "Joe Cannavo" <jpcannavo@y...> wrote:
> > --- In bigdob@yahoogroups.com, "Gregg" <starryskyn@y...> wrote:
> > > Royce has issued a statement that conical backed mirrors will have
> > a
> > > central zone that is aluminized and contiguous with the rest of
> > > surface.  Center spot application for laser alignment should be no
> > > problem.
> > Gregg

Paul,

> Maybe I missed it, but I didn't see anything about an aluminized
> center spot on that page.

If you follow the link about mounting the 8" and 10" sizes at the bottom of the
page, you will see that in those sizes the perforation for the mount does not go
through to the front surface.  For 12.5" and larger the perforation does go
through to the front face.

-- Steve Koehler
    steve_koehler@...

The information contained in this email message may be privileged, confidential
and protected from disclosure. If you are not the intended recipient, any
review, dissemination, distribution or copying is strictly prohibited. If you
have received this email message in error, please notify the sender by reply
email and delete the message and any attachments.

I'm now thinking along the lines of getting the Kendrick 2"
laser collimator and possibly using a Cheshire as well to
double check after I collimate with the laser.  However, can
one actually use the Cheshire at night time and be able to
see what one is doing?

-Chuck M.


--- In bigdob@yahoogroups.com, "Koehler, Steve" <steve_koehler@s...>
wrote:
> Paul,
>
> > Maybe I missed it, but I didn't see anything about an aluminized
> > center spot on that page.
>
> If you follow the link about mounting the 8" and 10" sizes at the
bottom of the
> page, you will see that in those sizes the perforation for the
mount does not go
> through to the front surface.  For 12.5" and larger the perforation
does go
> through to the front face.
>
> -- Steve Koehler
>    steve_koehler@s...
>
> The information contained in this email message may be privileged,
confidential
> and protected from disclosure. If you are not the intended
recipient, any
> review, dissemination, distribution or copying is strictly
prohibited. If you
> have received this email message in error, please notify the sender
by reply
> email and delete the message and any attachments.

Chuck,

> However, can
> one actually use the Cheshire at night time and be able to
> see what one is doing?

Absolutely!  You must not have seen one in operation.  When it's dark, you light
up the diagonal face with a diffused red flashlight.  (I taped a piece of paper
over the hole, and shine the flashlight through that.)  What you see through the
peep hole is a donut of red light.  The center spot shows up as a dark
silhouette on the bright circle.  [Whew! I don't know if I have ever had to
spell silhouette before.] If you're anywhere close to collimated, the center
spot is easy to see.  The only problem might be if your collimation is far
enough off to throw the center spot outside the Cheshire's circle.  This would
be a large collimation error, indeed (more than 1/2" off at the focal plane).
In this case, it's definitely easier to use the Cheshire in the daylight, where
the center spot is visible wherever it happens to be.  This will only be a
problem the first time you collimate, or if you have done something drastic,
like moving the mirror up or down a long way using the collimation screws, and
not turning all the screws the same amount.

-- Steve Koehler
    steve_koehler@...

The information contained in this email message may be privileged, confidential
and protected from disclosure. If you are not the intended recipient, any
review, dissemination, distribution or copying is strictly prohibited. If you
have received this email message in error, please notify the sender by reply
email and delete the message and any attachments.

As the owner of a 2" Kendrick laser collimator, I should warn you that
though this laser has a fancy spider-web grid to help align the return
beam, as with all single-beam lasers, it's still possible to have rotation
and tilt errors in the secondary and get a return beam.
I would supplement the laser with a good sight tube, like the Catseye
one, for secondary alignment and then use the laser for primary
alignment (especially if used as a barlowed source, where collimation of
the laser is not critical).  Of course, if you add a good cheshire, you won't
need the laser at all unless you plan to check in the middle of the night.
And if you add an autocollimator, you'll achieve closer collimation than
the laser.
The second issue with this, and all single-beam lasers, is collimation of
the laser.  If you enjoy spending time collimating your collimation tools,
then by all means go ahead--the Kendrick is a good one.
You may detect my not-so-subtle bias against lasers, but I have checked
the collimation on way too many scopes collimated by lasers and found
them mis-collimated to believe that any laser can be trusted unless you
yourself have collimated the laser to the accuracy of not moving off a
pencil point at 20' with full rotation of the laser.  And obviously, most are
not so well collimated.
Don Pensack


--- In bigdob@yahoogroups.com, "Chuck M." <turandot0@s...> wrote:
> I'm now thinking along the lines of getting the Kendrick 2"
> laser collimator and possibly using a Cheshire as well to
> double check after I collimate with the laser.  However, can
> one actually use the Cheshire at night time and be able to
> see what one is doing?
>
> -Chuck M.

When it's dark and collimation of the primary is far off, I just shine a
flashlight on the primary to find the centerspot. So it's not really a
problem. As soon as the spot is within sight of the cheshire (a matter of
seconds) , I put the flashlight away.

Jan
http://home.wanadoo.nl/jhm.vangastel/Astronomy/

----- Original Message -----
From: "Koehler, Steve" <steve_koehler@...>
To: <bigdob@yahoogroups.com>
Sent: Wednesday, August 31, 2005 7:04 PM
Subject: RE: [bigdob] Re: how to collimate a tscope T14 or a big dob?


> Chuck,
>
> > However, can
> > one actually use the Cheshire at night time and be able to
> > see what one is doing?
>
> Absolutely!  You must not have seen one in operation.  When it's dark, you
light
> up the diagonal face with a diffused red flashlight.  (I taped a piece of
paper
> over the hole, and shine the flashlight through that.)  What you see
through the
> peep hole is a donut of red light.  The center spot shows up as a dark
> silhouette on the bright circle.  [Whew! I don't know if I have ever had
to
> spell silhouette before.] If you're anywhere close to collimated, the
center
> spot is easy to see.  The only problem might be if your collimation is far
> enough off to throw the center spot outside the Cheshire's circle.  This
would
> be a large collimation error, indeed (more than 1/2" off at the focal
plane).
> In this case, it's definitely easier to use the Cheshire in the daylight,
where
> the center spot is visible wherever it happens to be.  This will only be a
> problem the first time you collimate, or if you have done something
drastic,
> like moving the mirror up or down a long way using the collimation screws,
and
> not turning all the screws the same amount.
>
> -- Steve Koehler
>    steve_koehler@...
>
> The information contained in this email message may be privileged,
confidential
> and protected from disclosure. If you are not the intended recipient, any
> review, dissemination, distribution or copying is strictly prohibited. If
you
> have received this email message in error, please notify the sender by
reply
> email and delete the message and any attachments.
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
>
>

--- In bigdob@yahoogroups.com, "paul_winalski" <Prune@A...> wrote:
> Maybe I missed it, but I didn't see anything about an aluminized
> center spot on that page.
>
> -Paul W.
>
> --- In bigdob@yahoogroups.com, "Gregg" <starryskyn@y...> wrote:
> > http://www.rfroyce.com/conical/  --it is best to go to the source.

The smaller Royce conicals are not perforated all the way through the
face of the primary mirror (as explained on their website.) However,
even if the mirror is perforated all the way through, there's nothing
stopping you from putting a primary mirror center spot on the actual
hardware instead of the primary mirror face. As long as the center
spot accurately defines the location of the primary mirror center (as
measured from the edge), it will still work with a Cheshire eyepiece.
If you plan on collimating at night--make sure you use a spot that
can be easily illuminated...

Vic

I was giving you a link that would have been leading to another page
by clicking on some hypertext: http://www.rfroyce.com/conical/mount%
20CFB.htm
When I wrote "a central zone that is aluminized and contiguous with
the rest of surface" I was putting into my own words these two facts:
1)the picture that shows a sample mirror on the test stand, with a
smooth front surface that appears fully aluminized, and,
2)the statement on the webpage "These mirrors have no holes in the
front."
I made an error by not refering to these two very specific ideas in
exact wording.

When you state " an aluminized center spot", you used your own words
to paraphrase my statement of "a central zone that is aluminized and
contiguous with the rest of surface", and were not quoting my exact
words.  Perhaps we both should be more careful on how we transform
the quotes and ideas of others when we post here.

--- In bigdob@yahoogroups.com, "paul_winalski" <Prune@A...> wrote:
> Maybe I missed it, but I didn't see anything about an aluminized
> center spot on that page.
>
> -Paul W.
>
> --- In bigdob@yahoogroups.com, "Gregg" <starryskyn@y...> wrote:
> > http://www.rfroyce.com/conical/  --it is best to go to the source.
> > --- In bigdob@yahoogroups.com, "Joe Cannavo" <jpcannavo@y...>
wrote:
> > > --- In bigdob@yahoogroups.com, "Gregg" <starryskyn@y...> wrote:
> > > > Royce has issued a statement that conical backed mirrors will
have
> > > a
> > > > central zone that is aluminized and contiguous with the rest
of
> > > > surface.  Center spot application for laser alignment should
be no
> > > > problem.
> > > Gregg

If you have a central perforation, it will of course serve as a central
"spot" (or, with the Royce mirror, the mounting washer) ! What you would
need is a white circle, a little larger than the spot itself arranged to be
centered around the optical axis near the focal plane, and a peephole also
centered on the axis (and of course ha hole in the white circle, large
enough to see the primary (at least the central part) through.

If the perforation/washer dia. is larger than the drawtube bore, you could
perhaps find a piece of tubing (or "plug) to fit if inserted from the
inside, making the white circle centered. That way, you will have a
"Cheshire" (or for that matter, the target to a Barlowed laser) designed for
your mirror. If smaller, a Cheshire isn't difficult to make, with an inside
"field stop" a little larger than the perforation/washer.

http://web.telia.com/~u41105032/kolli/kolli.html/#combination
http://web.telia.com/~u41105032/kolli/kolli2.htm#mkcombination