RE: [APML] E210 Coma

[Kirk Carbo <kcarbo@lobosservices.com>]

Gene,

Thanks for the response.  Can you tell me how to get in touch with Charlie
Thomas.  I am not having much success in getting a definitive answer from
Takahashi representatives.

Kirk Carbo

> -----Original Message-----
> From: Gene Horr [mailto:genehorr@houston.rr.com]
> Sent: Thursday, May 08, 2003 11:31 AM
> To: Discussion of Film Astrophotography
> Subject: RE: [APML] E210 Coma
> 
> 
> >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
> 
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