[ATM] Ghosting in a Refractor

[mckernan at murdoch.edu.au (Ian McKernan)]

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!

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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!!

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