Re: [APML] TMB 105mm f/6.2 - What's this Aberration?

["Chris Cook" <ccjd@ix.netcom.com>]

Looks like a classic internal reflection in the FF.  Possible poor coatings.
Good to see you shooting!  You've been quiet for a while.

Take care,

Chris

-----------------------------
Chris Cook Photography
www.cookphoto.com


----- Original Message ----- 
From: "Jon Kolb" <jkolb@datawest.net>
To: "'apml Astrophotography'" <astro-photo@seds.org>
Sent: Wednesday, September 22, 2004 2:02 PM
Subject: [APML] TMB 105mm f/6.2 - What's this Aberration?


> All,
> 
> Markus Ludes suggested that I post these images to the group to solicit
> your thoughts on what might be causing the blue halo on Deneb, and on
> every other bright star in the frame.  The degree to which the halo
> shows up is in proportion to the brightness of the star, and to see it
> on other stars it's necessary to look at the blue channel.  A close crop
> of Deneb in color, and of 56 and 57 Cygni in the blue channel can be
> seen by scrolling down the page.
> http://home.datawest.net/jkolb/tmb105test.htm
> 
> Gamma Cygni and other bright stars show the same thing in other shots I
> took that night.  Note that the problem is not atmospheric, since the
> TMB152 was shooting the same subjects simultaneously, using the same
> film and camera type, and shows no such reflections.  For the same
> reason, the film (E200) can be ruled out, since I was using the same
> film on the 152, and have used it for several years with various
> instruments and the same camera without incident.
> 
> These are the first shots taken with this instrument, and details of the
> exposure, etc. are on the webpage.  My personal opinion is that this is
> an internal reflection caused by either the lens or the field flattener.
> Markus says the lens cannot cause this problem.  
> 
> Other hypotheses are appreciated.
> 
> Sincerely,
> Jon Kolb
> Adventures in Astrophotography
> http://home.datawest.net/jkolb/
> Life Member, International Dark-Sky Association
> jkolb@datawest.net
> 
> 
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