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Re: [APML] Schmidt camera dismanteled
Robert,
Even though I don't own a Schmidt camera, I enjoyed reading your manual and
learned a lot. As you embark on this journey, please take lots of detailed
close up photos and post them. It would be most informative.
Rick Kellogg
----- Original Message -----
From: "Robert Reeves" <reeves10@swbell.net>
To: <astro-photo@seds.org>
Sent: Sunday, June 09, 2002 9:37 PM
Subject: [APML] Schmidt camera dismanteled
> Greetings fellow Schmidt camera owners,
>
> My adventures in overhauling my 8-inch Schmidt camera continue...slowly.
>
> I have decided to have Clausing apply their 98% reflective Diamondbright
> coating to the mirror (unless some one knows a reason why I shouldn't use
> this???) But the $100+ cost of it has me in a hold right now because the
> 9-to5 daytime job is real slow now for some reason. So I decided to take
> the camera appart anyway, then reassemble it with the existing mirror just
> to make sure I can do it right and get it properly collimated and
refocused.
> This is a training run before I fiddle with a pristine mirror.
>
> After worrying about taking it appart, disassembling the 8-inch Schmidt
was
> rather easy. After marking the tube where all the shims and corrector and
> mirror orientation went, I pulled the mounting screws out of the
collimation
> adjuster backets and cut through the silicone with an Exacto knife. I
found
> that buried inside each silicone pad glueing the mirror in place was a 1/2
> sqaure inch spot of bakalite which acted as a pad between the mirror back
> and the collimation adjusting screws. Once these were out and the
silicone
> cleaned off the back of the tube, the mirror fell right out. Wow! An
> 8-inch f/1.5 mirror is a deep bowl! For those who wondered, the mirror is
> 8.75 inches in diameter and the cell masks it down to 8.5 inches in
> diameter.
>
> The corrector plate had four sets of paper shims around the perimeter of
the
> glass. Each was a stack of three to six thin strips of paper slightly
> heavier than typing paper. I guess Celestron chopped up whatever was
handy.
> There was printing on the paper, but it was too cut up to understand what
it
> said. What really suprized me was how chipped up the edge of the
corrector
> was. It is chipped almost all the way around its rim. This must have
> happened at the factory because there are no chips in the holding cell.
> None of the chipping is visible once the retaining ring is in place.
>
> I have heard Celestron made the correctors out of ordinary window glass.
I
> don't know if this is true, but the thickness of the corrector is very
> similar to window pane glass. Contrary to what I was told, I can tell
which
> side of the corrector has been ground into the Schmidt corrector shape.
> When I looked at the reflection of straight lines that were at an angle to
> each other, such as the roof and side of my house as seen out the garage
> door, the corrector side showed those straight lines as mushy and bowed
> compared to the mormal reflection from the flat side of the corrector.
The
> corrector was 8.5 inches in diameter and is masked down to exactly 8
inches
> by its retainer.
>
> There was one cork shim about a half inch wide every 120 degrees around
the
> rim of the mirror centering it in the cell and there was a small 1/4-inch
> square spot of cork (very flattened) under the lip of the cell where the
> Invar rods meet the face of the mirror. There is certainly no effort to
> make any floatation support for the mirror. It is simply held into its
cell
> by being pushed into place with the three bakalite pads under the
> collimation jackscrews, then being siliconed in three places.
>
> Now I can see why some Schmidt cameras produce good images while others
> produce fantastic images. It looks like the mirror can be warped slightly
> in the cell if it has to be pushed hard on one side to achieve
collimation.
> I think mine is a "good image" Schmidt :-( I saw an 8-inch Schmidt image
> years ago in S&T that was taken by John Gleason. His camera clearly makes
> better images than mine used to. After I get through tinkering with it,
who
> knows? Maybe I can get this puppy to sing for supper too!
>
> Anyway, over the next several days I will be adding these adventures and
a
> few more things to my Schmidt camera guide on my web site.
>
> Robert Reeves reeves10@swbell.net
> 520 Rittiman Rd. www.robertreeves.com
> San Antonio, Texas 78209 210-828-9036
> USA 29.484 98.440 200 meters
>
>
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