Re: [APML]: OAG & Illuminated Reticule Causing Reflection

[Bert Katzung <katzung@pacbell.net>]

EdwardsNo1@aol.com wrote:
> 
> 
> Jim,
> I'm very sorry, but the goal posts have moved somewhat. It seems that I have a
> Meade "CCD" OAG with extension tube to the rear and Newtonian adaptor to the
> front. However, I believe the main body to be identical to the photo OAG, but
> probably with the prism positioned further into the optical path.
> 
> Apologies for messing you about with inaccurate information, I assumed I had a
> photo OAG.
> 
> Can I adjust a Meade CCD OAG to perform well as a photo 35mm OAG ?
> 
> Regards,
> Steve Edwards
Steve: I've been watching your emails with great sympathy because I've
got the Meade OAG also and have trouble with it. However, my trouble is
entirely different (can't find stars in the off-axis finder). Your 
mention of a "CCD OAG" rather than a "photo OAG" has me completely
confused. I didn't think there were two different OAGs. I suspect
that you may have a different fitting on one or another port of the OAG
that is messing things up and giving the impression of being suitable
for CCD rather than photo accessories. Another thing that is confusing
me about your problem is the "reflection" that you get. A reflection of
what? 

Going back to the basics of my OAG, If I strip it down to what came in
the box, I have a black metal cube with "Meade OFF-AXIS GUIDER" on one
side. on the left is the ring for coupling it to the scope, on the right
is the tube (with a knurled [roughened] section) that has a T-thread for
attaching the camera adapter, and sticking up is the long fixed tube
for the eyepiece or CCD guider. On my OAG the knurled tube on the right
can be unscrewed and replaced with anything else with a T-thread. 
Looking through the camera adapter end toward the scope end, I can
see the prism sticking down about 5 or 6 mm from the vertical tube. It's
about a centimeter wide and shouldn't obstruct anything except in that
small area (6 mm x 10 mm). In fact, in the few photos I've taken 
through my other OAG (a lumicon), I can see the *shadow* of its prism
at the edge of the photo, but nothing I would call a reflection. I
haven't taken any photos with the Meade OAG yet, so I'm not sure whether
I will get the same shadow effect, but I wouldn't be surprised if I do--
it's in the main optical path, so I would expect it to show up.

Now, looking down the eyepiece tube, I *can* see a reflection--the 
reflection of whatever the prism is aimed at. Playing with it just
now I find that the upper part of this tube can also be unscrewed, 
leaving just the prism housing on top of the central cube. This is
to make it easier to adjust the prism, I suppose--there is a tiny
setscrew at the side of this circular housing for loosening and
repositioning the prism.

Moving now to the coupling end of the OAG, I got mine to use with an
SCT, not a Newtonian, so if you got yours for a NEwtonian, it might
properly have a different coupling. My coupling is a captive female
threaded ring and can be removed by unscrewing an inner retaining
ring. I noticed when I got the OAG that the inner retaining ring was
rather loose and allowed the whole OAG to flop a bit, even with
the coupling ring tightened up the scope quite firmly. In fact, even
after I tightened the retaining ring, it has a tendency to loosen up,
so I try to remember to tighten it up periodically. If all of the 
above descriptions fit your OAG, maybe a very loose retaining ring
is the problem--by allowing the body of the OAG to droop down off the
scopes optical axis.

All of the above ruminations may be inapplicable to your situation
but they have allowed me to think through my OAG arrangement, so 
thanks for raising the issue and good luck!
Bert Katzung