Posts Made By: John Biretta

I'm not an expert on oiling lenses. It's probably
difficult to know what it was oiled with, and hence
hard to predict long-term issues like haze. I'd suggest
to make some tests.

(1) Try to rule-out some sort of turn-edge or
oil problem right a the edge. Make some cardboard
or black paper masks with say 75mm, 70mm, 60mm holes
and see if masking off the outer bit of the lens makes
some large improvement on bright objects. Maybe it
won't, but easy enough to try it. If something like
a 75mm masked fixed it, I might be tempted to
make a more permanant mask and otherwise leave it alone.

(2) Try shining a laser pointer through the
lens and see where the light goes. Does the laser
beam gain some halo when shined through the lens
that not there alone, or with similar lenses.
Does the beam show a lot of light scattering
at either of the surfaces or the oil space.
I'm wondering here if the front surface
might be pitted or hazy.

(3) Get the lens + cell off the scope and hold
it up to a bright light. Does anything look hazy?
Is the haze in the oil space? Front surface?

I expect a reasonably capable ATMer could attempt to
re-oil the lens. Assuming the elements separate easily, you could
clean them well with 91% rubbing alcohol. Get some
high viscosity immersion oil from your favorite microscope
supply outfit. I might consider adding three spacers
around the edge (thin adhesive tape) to make future
disassembly easier. Put a couple drops of oil
on the concave side and slowly/gently lower the
convex side. Obviously you need to avoid bubbles.
Wipe excess from the edge and seal the edge it with something like
electrical tape (being mindful that it needs to fit
back in the cell).

Where I think you could get into trouble, is if the elements
don't want to separate. Then some experience as to using
solvents or mechanical means would be very valuable.

Alan mentioned two outfits that might work on it.
Some other people who probably have the skills are
Wolfgang Rohr (Germany)
http://rohr.aiax.de/hp_new/
and Roger Ceragioli (Arizona) who has made some oil-spaced lenses.

Also Markus Ludes (Germany) can probably refer you to people
with experience re-oiling old Zeiss lenses.

There is some discussion of oiled lenses at
http://bobmay.astronomy.net/refractor/Refrdesign.htm

Good luck!

This is a brilliant web site for optics tests. Not
only reflectors, but APOs, achros, MCT, SCT, etc.
Good to re-post it now and then.

Excellent eyepiece!

I take it you mean the Orion "Flip Mirror"? I've
used two of these. They are very nice in most
respects. Machine work is excellent. Good
adjustments available to collimate the mirror
so as to get the two exit ports aligned. Nice
focus adjustment on the eyepiece side.

All the ports use T-connections, so it is very easy
to re-configure and connect with other T-devices.
If you've got a T-thread filter wheel, or a T-thread
Barlow or PowerMate, you can just thread it all together.

The one negative aspect, is that the mirrors are pretty
bad optically. They are fine for aligning the
field of view, centering targets, etc. But if you
also want to use the eyepiece port to get a fine
focus on the camera, you can pretty much forget
about it. The view with a 5 mm eyepiece will show
several waves of astigmatism, making focus very
indistinct and hard to set accurately. It would be
nice if you could see the Airy disk in the mirror
and use it to set the focus, but not on these. On the
other hand if you just want it for centering the
target, and maybe getting a rough focus, then it
will be fine.

Some flip mirrors I tested from other makers had
really nice mirrors, but were terrible in
other respects. So I can't offer advice on a
"best" alternative model.

I've sometimes used tape to attached stuff to my
Celestron SCTs. Occassionally the item falls off,
and turns out the paint has pulled away from the
aluminum casting.

Out of curiosity: which fans are you planning
to use? I may try this on my C8 someday.

Very sharp! Why the blue filter --- why not a red filter?

I see what you are saying, but I don't think
backlash plays much role in wind driven vibration.
I usually leave plenty of backlash in the worm
adjustment, and that backlash corresponds to a huge
motion of objects in the field (at high powers like
500x). I can grab the scope and move it to the other
side of the backlash, and its a huge motion.
But I'm not seeing that large motion in wind conditions.
Instead I see very small motions. What I see happening,
is that the wheel gear settles against one side of the
backlash (due to either slight off-balance or drive
direction for RA) and stays there.
The wind-driven vibration is instead caused by
everything from the ground to the scope bending and
flexing slightly.

Maybe if the wind completely changed direction every
few seconds, I guess you could get the backlash coming in.
Like if it came from the East for 1 second, then from
the West during the next second, then from the
East again during the third second, etc.
But instead what I get is wind from a nearly constant
direction, which varies in velocity (pressure).
Everything flexes in proportion to this side-ways
variable pressure on the tripod / mount / scope.

Some vibration sources I found in my G11 stepper
were:

Poor machining of the pier top / mount bottom joint.
Essentially the mount head was contacting the
pier top at only one or two places, and was rocking
back and forth on the pier top. Some simple shims
fixed the problem and gave 3-point contact.

The steppers ran at something like 1/2 arcsecond
steps, which showed up as a 1/2 arcsecond blur
on targets (depending on the mount load, pointing
direction, etc.). Gemini was better in this regard.

The RA worm gear was somewhat free to move along its
axis, adding a sort of springy motion in RA.

Without knowing what you have there, its hard to give specific suggestions.

If you have a working telescope with all the components, the best option might
be to simply clean the parts yourself (get some advice from the Unitron
forums, being extremely cautions to not damage anything) and sell it that way.
Take lots of photos of good and bad aspects, and advertise it on Astromart.
I think many folks would be willing to accept some range of normal wear
(but not abuse) on these -- it need not look perfect.

If it is not a working scope (missing key parts, or parts broken) then its
a much more complex question. If you know a good restorer who can exactly
duplicate the missing/broken parts (indisinguishible from new) that path
would have a considerable amount of emotional appeal. And I feel it could
sell for numbers approaching a scope with all original parts. But if the
restore work will result in extra screws / mending plates / obvious repair patches,
then I think the value would be adversely impacted -- it would bring more
than selling it "as is", but far below a proper scope with all original
parts. There is some obvious economic risk in such a restore -- it might
be possible to spend a lot of money on the restore work, and not recoup it
at sale time.

As for selling it off as parts. I think the success of this will depend on
exactly which model and which year it is. These went through many variations
over their >40 years of production, and parts from one year do not necessarily fit
scopes from a different year or model. If it is one of the early or rarer
models, it may be hard to find a buyer for the parts (though they might be willing
to pay a lot). If it is one of the later versions, you might have good
success selling off any major components in good working condition (tripod assembly,
equatorial mount, motor drive, photo guide scope, OTA, etc.). Often people
will have an OTA but not a mount, or a tripod in bad condition, or need a drive, etc.

Regarding markets, Astromart is ideal in many ways -- you can post many pictures
and have a very targeted audience. In conjunction with this, you could mention
on the Unitron forums that you have the scope up for sale on Astromart. Another
approach, especially if it is an excellent restore and shows well, would be to take
it to conventions (NEAF, Stellafane, RTMC, etc.) and indicate on Astromart and forums
that you have it for sale, and well be at such-and-such convention with it.
This would give serious buyers a chance to look at it first hand and evaluate
the quality of the restore work, etc.

You are in an enviable position there. Good luck!

Yes, for DSLR work I would recommend the F/4 Newt over the F/10 SCT.
Advantages are brighter images, shorter exposures (hence less dark
noise / hot pixels, also less impact from tracking errors), and wider field.
You would need a coma corrector, but these are easy enough to find and use.
The Newt might need some initial work to collimate the optics to your
satisfaction, but SCTs also can have collimation issues.

You mean the big bolt that fastens the mount to the tripod head?
I'll try to check tomorrow.