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Subject: Optical Window Problem...
By: Anonymous (xxx.xxx.163.100)
Date: 07/07/2002 03:06:06 pm PDT
Just wanted to share a possible fix for some Astroscans:
My friend has an old Astrscan that was showing peculiar image doubling. The problem would not go away, even after cooling thouroughly.
I suspected that there was a problem with how the window was being held. I removed the window (very easy, just a steel snapring...) and examined the area where the window sits. I found little globs that had squished out when the OTA was glued together. I postulated that pressure from the snap ring was bending the plate over the 2 globs of glue.
I cut the globs out with a sharp knife and re-installed the window and snapring. The images were instantly perfect (for an Astoscan). Previous to the fix, the 'scope maxed out at 50x. It now holds power reasonbly well to 150x, with enough resolution to split Epsilon Lyrae. I've seen other astroscans with the same problem, and I wonder if this may be a quick easy fix for other OTA's. I'll be trying this with another friends Astroscan in the near future, I'll post the results.
I've wondered many times if the window is the primary culprit in poor performance- I've heard it's VERY difficult to make optical flats of this size and still keep them fitting into the price range of the Astroscan. I've considered getting rid of the window in mine, in favor of replacing it with a curved spider... In the meantime, perhaps some will find this fix acceptable.
Subject: Astroscan Fix
Date: 09/12/2002 04:26:35 pm PDT
Thank you for the info!! I will give that a try. My optical window is rather streaky... perhaps removing and cleaning will help.
I also think removing the optical window would be a good idea. Also downsizing the secondary to a 0.8" will increase contrast. Older Edmunds had great optics but rather oversized in the secondary. I have downsized the secondary in my 4.25" f10, 6" f6's, and my 6"f8 with great results.
Subject: Re: vote by xxx.xxx.225.156
By: Anonymous (xxx.xxx.193.233)
In Reply to: Anonymous (xxx.xxx.225.156) (Original Vote)
Date: 02/02/2005 09:05:20 pm PDT
Just started an Astroscan discussion group on yahoo. If you are a fan of the astroscan I encourage you to join. You will find it in yahoo groups under edmund astroscan. Look forward to hearing from you.
>Astroscans have pretty good optics on the whole with the possible exception of the optical window. Just received my brand new astroscan in the mail today and have fairly clear skies....imagine that. If you get lucky as I have and receive an astroscan with really good optics you have something. I was a little worried at first because the shipping box said made in China. I needn't of worried. The optics star tested clearly better than 1/4 wave and the optical window with its fresh coatings didn't distort the fairly flat field nearly as much as I've seen in previous astroscans. A lot about the astroscan has already been said...the simplicity of the mount, wind proof, maintenance free, durable metal peep sight. I did find it interesting that the peep frames the field of view of the scope pretty closely. I would like to add that Edmund has made a substantial improvement in its 28mm eyepiece. The original 28mm RKE was pretty popular with its generous eyerelief, good light throughput and overall sharpness. However it had a tendency to focus the dust on the field lens along with the telescopic image. The 28mm plossl solves that problem and increases its advantage with good coatings and a wider field stop(afov). The 2 eyepieces alone will be worth $60 on the used market. I'm keeping mine however. The long eyerelief makes them really good eyepiece projection photography eyepieces.
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