Sorry for my failure to credit accurately, Matt. I discard my e-mails too
soo, it seems.

Glad to see Herb interested in the discussion. I will await his results
with considerable interest.

Phil

----- Original Message -----
From: "Matt BenDaniel" <matt@...>
To: <astro-photo@...>
Sent: Thursday, January 18, 2001 4:50 PM
Subject: Re: [APML] Pentax 6x7 -- obstructed light path?


> At 02:48 PM 1/18/01 -0800, Herb York wrote:
> >----- Original Message -----
> >From: "Philip C. Farnam" <p.farnam@...>
> >To: <astro-photo@...>
> >Sent: Thursday, January 18, 2001 2:18 PM
> >Subject: [APML] Pentax 6x7 -- obstructed light path?
> >
> >
> > > Follow-on to previous discussions about uneven-illumination and/or
> > > "hot-spot" on Pentax 6x7 negatives exposed through Tak FSQ106, Pentax
> >EDUF,
> > > and other instruments.......
> > >
> > > One poster quoted Roland Christen of Astro-Physics as saying
> > > hot-spot/vignetting/uneven illumination (one of those, anyway) was
> >primarily
> > > owing to "obstructions in the light path."
>
> That was my post.
>
> > >
> > > My Pentax 6x7 camera body has lens breach opening of less than 3"
while
> >the
> > > corner-to-corner dimension of 6x7 negative is more like 3 1/2."
Perhaps
> > > this would represent the "obstruction" to which Roland primarily
refers.
> > > Does this mean that the Pentax 6x7 is more-or-less chronically prone
to
> > > uneven illumination -- especially with longer lenses and lower
f/stops?
>
> No. But for fast optics to evenly illuminate the film, the telescope
designer must somehow get the light cone into the camera without being
obstructed by the body opening or anything else.
>
> > >
> > > Are all MF camera bodies like this or are there some with body
openings
> > > having diameter same or greater than negative's corner-to-corner
> >dimension?
>
> It is much easier to design an optical system for a custom camera with a
large opening.
> There aren't many such cameras off the shelf.
>
> > >
> > > Or am I obsessing on a meaningless theme?
> > >
> > > Phil Farnam
> >
> >
> >Very interesting - this is the 3rd group (at least) that I have seen this
> >same information.
> >Tony Hallas tells me he can take any FSQ106 shot and process it with no
> >"HOT" area now.
>
> Does Tony have a custom camera body with a larger opening?
> What do you mean "process"? Flat-fielding?
>
> >I have sitting right in front of me 2 Pentax 6X7 lenses - a 400mm f/4
EDIF
> >and the 800mm f/6.7 EDIF. Neither has a 4" mounting to the 67II cameras
but
> >connect directly.
> >I contacted Pentax's tech guy and asked if these lenses will FULLY
> >illuminate the 6x7 film in the 67II cameras. The answer was "we made them
to
> >do that". In February a bunch of us are going to Arizona for about 10
days
> >and I'm taking these lenses with us and I will send some shots to Tony to
> >see what he thinks.
>
> Optics that bring the light cone far enough back toward or into the camera
opening are not vignetted by the opening.
> That is a hint as to what Roland is designing for the Traveler.
>
> >If they do FULLY illuminate the 6x7 film and have pinpoint stars and
> >excellent color correction then we may have a winner. I let you know.
> >Thanks
> >Herb
>
> --
> Matt BenDaniel
> http://starmatt.com
>
>
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>


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