[ATM] Ghosting in a Refractor

[kurt.clement at flashmail.com (Kurt Clement)]

I just built my first scope, a copyscope, and there is indeed a flare, or 
ghosting problem when looking at the moon.  I don't  notice it as much when 
looking at Jupiter, I can't push it much past 50x anyway, but it is enough 
to resolve the planet from the rings (240mm FL, 50mm aperture).   It also 
has a noticable coma problem.  But for a $11 lens from Surplus Shed it 
gives great wide field views of Pliedies, Hyades, Orions belt and sword, 
and I'm having a great time with it.  I built a pipe EQ mount and a nice 
oak tripod, put together a red-dot finder, and the folks at my local 
hardware store walk the other way when they see me coming in these 
days...  My lens is coated, but barely.

Kurt Clement
Nixa, MO



  At 12:21 PM 2/6/04 +0800, Ian McKernan wrote:

>Hi!  I recently bought a cheap, 80mm diam, 400mm fl,  air spaced doublet 
>refractor lens that i have made up into a small telescope. It much like i 
>imaging a "Copy-scope" would be. Eventually it will be a big finder.
>
>Problem i have is with "ghosting".  When i point it at a large, bright 
>object, like a planet i see a nicely focused image in a large cloud of 
>brightness so it washes out any detail. Not that i'm going to see much at 
>the low magnifications this scope gives, but it is annoying.
>
>I have read a bit on the web and i seem to have a "Baker" design where R2 
>and R3 are the same radius.  I think that the "ghosting" is caused by 
>reflections between these two surfaces.  Have looked at getting these two 
>surfaces coated, but that would cost 10 times what the lens did.
>
>The spacer is a plastic ring, and i tried placing an extra, paper spacer 
>in there to increase the air gap. It helped a bit with the ghosting but 
>seemed to muck up the spherical correction slightly.
>
>Anyone out there have any ideas on how i may be able to improve things, or 
>if the lens is the problem at all??  Could it be something in the way i 
>built the scope??
>
>Thanks!
>
>*********************************************************************
>Ian McKernan
>Plant Biology Technician
>
>         c/o Murdoch University
>         Division of Science and Engineering
>         School of Biological Sciences and Biotechnology
>         South St Murdoch  6150
>         Western Australia
>         tel: + 61-08-9360 2206
>         fax: + 61-08-9360 6303
>
>Don't let the Dogma Bite!!
>
>*********************************************************************
>
>_______________________________________________
>ATM mailing list http://www.atmlist.net/
>
>
>
>
>---
>Incoming mail is certified Virus Free.
>Checked by AVG anti-virus system (http://www.grisoft.com).
>Version: 6.0.576 / Virus Database: 365 - Release Date: 1/30/04
-------------- next part --------------

---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.576 / Virus Database: 365 - Release Date: 1/30/04