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

[Éder Iván <eder@prof.hu>]

Hi Jon!

I have the 130mm F/6 model with the newest FF and the old Pentax 6x7 
camera. I don't have any similar problem with it, even around Gamma Cygni.
However, I use my own designed tube and focuser.
But my friend has the same instrument with the old FF and he gots some 
reflection in the image of Pleiades. Not around the bright stars, but in 
other places on the image are clearly visible.

I think the incorrect spacing (FF to focal plane) may cause this problem 
(or the correct spacing?). The space in my instrument is 114mm from the 
very center of the last element's surface of the FF to the focal plane.


Clear skies

                 Ivan       (not that! ;-)

At 20:02 2004. 09. 22., you wrote:
>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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