Posts Made By: John Biretta

Focusser needs to go IN by 10.0mm after swapping
in the Klee 2.8x (for 19mm Panoptic).

Yeah, I've had a little experience with it.
Check out

http://radiojove.gsfc.nasa.gov/

My guess is that no one will want to
touch the Fluorite element. I think
Takahashi is the only one out there coating
Fluorite; most other makers don't coat
the Fluorite element at all (too fragile).
If the problem is the other element, try
http://www.majestic-coatings.com/ on the
astromart home page.

Sounds to me like you've got a trace of coma from
slight mis-collimation like Mitch says. I was able
to fix this in my ETX-90 my tweaking the collimation
screws behind the primary mirror. But I have no idea
how you'd make the same adjustment on a Starmax.

I've attempted to remove corrector plates from a
C5 and C9.25 so can (briefly?) comment. First, be
aware the $100 will later seem cheap if you screw-up
the scope. So be sure you really want to go down the
"do it yourself" path. Secondly, make sure the
optics are really dirty -- a little dust or haze will
not hurt anything. During the daytime, take the
caps off the scope, take out the eyepiece, and
point it at a plain white wall. If you can't see the
dirt when looking in the back of the scope, its
probably not worth the trouble to clean it.

Alright, assuming you really want to do this...
First make a nice clean area to work. Maybe a large
table with some soft towels on it to pad the tube
and later the corrector plate. Place the tube so it
is horizontal with the front of the scope slightly
higher than the rear of the scope.

There is usually a thin black retaining ring at the front
face of the scope which holds the corrector plate in.
This ring is held in by a number of small screws.
OK, so first mark the retaining ring and the tube
so you can get it back on in exactly the same way
(use tiny bit of tape, etc., to mark). Remove the
small screws. The retaining should come right off.
Mark the edge of the corrector plate (now visible)
in the same place as you marked the tube and retaining
ring. Also note if there are any shims around the
edges of the corrector plate to keep it centered --
some scopes will have these -- if there are shims,
carefully mark them and mark their locations.

Now the fun begins. Using cotton gloves or piece
of soft cloth, grasp the secondary holder at the
center of the corrector plate, tilt the front of
the scope downward slightly, and tip out the
corrector. Maybe it helps to have a friend hold
the scope while you do this.

(continued....)

Here's the snag. In both cases I tried, the back
face of the corrector plate rests against plastic
pads which are slightly sticky, so it may not
come out right away. On the C9.25 I was able to
use a thick toothpick and gently pried the edge
of the corrector plate slowly working my way
around the plate until it came loose at one spot,
and finally came loose all around the circumference.
Then I could just lift out the corrector.

However on the older orange C5, the corrector
was really stuck in there on these pads, and no
reasonable amount of prying did anything. I
gave up on that one, and put it back together.
I think gently heating the scope (put it in
small room (bath room?) and put the heat up to
80 or 90F for couple hours) might have fixed this,
but did not try it.

Assuming you do get the plate off, any generic
advice for optics cleaning will suffice. Sterile
cotton balls and solution (1 pint 91% isopropyl
alcohol, 1 pint distilled water, 1 drop plain
dish soap) works well. Canned air or
"Dust-Off" helps alot. First used canned air to
blow dust off surface. Use the solution and
cotton balls next -- completely wet cotton ball
in solution, using only weight of the wet cotton
ball, make one straight swipe on the surface, and
throw away the cotton ball. Get another one, and
repeat until you've done the whole surface. Then
repeat entire surface with plain distilled water
to rinse. Finally use canned air to blow off
water droplets, and blot edges of glass as needed
with paper towels to absorb water as it comes off
the optic. Put it in a clean place while any
remaining traces of water dry off.

Good luck. And consider again sending it to the
experts at Celestron.

No. Chromacor is a zero-power device. Entrance
and exit surfaces are flat; internal elements
appear cemented. It uses thick glasses with strange
dispersion properties to delay/advance focus of
different wavelengths. There is also some correction
for sphero-chromatic aberration. Some also have
correction for spherical aberration (O and U models).

I would highly recommend John Hopper at
astrobuffet.com as source for Chromacor.
I've bought several from him and from others;
I would definitely say Hopper is the best.
Knowledge, packing, and service are superb.

I am not sure if he still offers the Synta
matching service.

Marty,

Quick answer is "yes, it does approach APO views."
But you do have to put in some work to get there --
collimation of the Synta needs to be pretty good, and
you may need to experiment with spacing / rotating
the Chromacor in your scope. But if you like tinkering
with this stuff, you'll have alot of fun and get some
great views when you're done.

Here's a couple of my past posts on the subject:

http://www.astromart.com/messages.asp?message_id=2777

http://www.astromart.com/messages.asp?message_id=4220

http://www.astromart.com/messages.asp?message_id=24960

http://www.astromart.com/messages.asp?message_id=30411

http://www.astromart.com/messages.asp?message_id=39481

G-11 should be fine; probably even a little more
mount than you need. I used it on a CG-5.

Best wishes, - John B.

Heres a couple guesses:

1) They look alot like filter internal reflections.
Are you using a UV or skylight filter?
Try another shot without the filter, or get a multi-
coated filter.

2) The vertical streak appearance of the reflections
is probably due to some vibration when the shutter is
tripped. Its also visible on the bright star images
themselves. You seem to get it at the very start and very
end of the exposure. Try covering up the front of the
lens with a large sheet of cardboard while you operate
the shutter release.

3) If it still persists, think about your scanner. Could
also be there. Get a magnifier and see if the streaks
are actually on the film or not.