RE: [APML] E210 Coma

["Gene Horr" <genehorr@houston.rr.com>]

>From my experience Mitsuboshi is, ah, perhaps mistaken.  Charlie
Thomas (a very experienced film imager) had a problem with his
custom adapter and the distance involved was much less than 10mm.
When he got the adapter to the correct spacing all of the edge
problems went away.  IIRC he was using a 6x7cm back.

Gene Horr
genehorr@texas.net



-----Original Message-----
From: astro-photo-bounces@seds.org
[mailto:astro-photo-bounces@seds.org]On Behalf Of Kirk Carbo
Sent: Thursday, May 08, 2003 10:51 AM
To: APML (E-mail)
Subject: [APML] E210 Coma


I just developed my first set of photos from a Mitsuboshi 6x9 vacuum back
camera on Techpan film.  The Epsilon 210 is supposed to provide a 57mm image
circle per the Takahashi specs.  I see coma radiating away from the center
of the image starting at about 30 to 35mm.  So I am actually getting a 35mm
image circle with good focus.  I am starting the process of solving this
problem and I would appreciate any input from the group.  Here are the
factors I have determined so far.
1)The Mitsoboshi camera film plane distance from the Ross corrector is set
about 10 mm closer than the Tak spec of 68.6mm.  Ted Ishikawa at Hutech says
this is based on field tests done by Mitsuboshi in Japan and that the Tak
spec is a design spec and not field tested.  This placement will cause the
corrector lens to get less of the light cone.  Is this a factor?
2)The KEF is currently set at the same distance as the film pressure plate
in the camera, 58.45mm.  The Techpan is .120(120 microns) thick.  So I
should move my focus back 120 microns to place the film surface at the exact
focus.  The 35mm circle in the center of the image is in focus now, so the
depth of focus must be helping this a little.  My understanding is focus
doesn't cause coma anyway.

Kirk Carbo
Lobo's Services
Ph: 800-225-0899
Fax: 225-677-8277

_______________________________________________
Astro-Photo mailing list
Astro-Photo@seds.org
http://seds.org/mailman/listinfo/astro-photo

_______________________________________________
Astro-Photo mailing list
Astro-Photo@seds.org
http://seds.org/mailman/listinfo/astro-photo