[rollei_list] Re: 6 x 9 search

Thanks for the math, Richard. We are talking 2 x 3 and not 3 x 4...
don't have enough fingers and toes to know if that will make  a
difference... I have shot plenty of chromes with a 65 mm SA on 23 and
don't see a stop of fall off in the corners by casual examination
(much less a stop and a half as was originally posted)... guess a test
in in order. I've also shot a ton of 67 chromes with a Koni Omega 58,
which is roughly a SA design, and see virtually no fall off at all...


Eric Goldstein

--

On 8/30/07, Richard Knoppow <dickburk@xxxxxxxxxxxxx> wrote:
>
> ----- Original Message -----
> From: "Eric Goldstein" <egoldste@xxxxxxxxx>
> To: <rollei_list@xxxxxxxxxxxxx>
> Sent: Thursday, August 30, 2007 4:32 PM
> Subject: [rollei_list] Re: 6 x 9 search
>
>
> > You're way off relative to a 60ish mm lens shot on this
> > format... the
> > light fall off (not vignetting) is not anywhere close to
> > an f/stop...
> >
> > Eric Goldstein
> >
>    The half angle of a 60mm lens on 3x4 is around 40degrees.
> The fall off of an ordinary lens is around cos^4 theta where
> theta is the half angle. Lenses with tilting entrance pupils
> have less than this, closer to cos^3 theta. For a cos^4 lens
> its about 0.34 of the light at the center, for a cos^3 lens
> its about 0.44. One stop is 0.5, i.e. half the light, so
> either type will be down somewhat more than a stop at the
> corners. A Super Angulon is has a tilting entrance pupil.
> Older WA lenses, like the WA Dagor or Series V Protar are
> around cos^4, some older very wide angle lenses like the B&L
> Metrogon have even more than cos^4 theta fall off. For B&W a
> 60mm on 3x4 or 90mm for 4x5 is acceptable but one would
> probably want to use a center filter for color work,
> especially transparencies.
>
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@xxxxxxxxxxxxx
>
>
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