Okay. All you had to do was ask. :-)
The cameras: OM-4Ti with 2-13 screen, Mamiya RB-67 with regular split-image WL
viewfinder
The lenses: 50/3.5 Zuiko Macro, 127/3.8 Mamiya Sekor C (Don't have a 3.5 lens
for the Mamiya, but I figured this was close enough.)
The light source: 13x17 in. slide viewer at 1 ft.
The measuring device: Sekonic Digi Master L-718 meter using the ground glass
probe
The difference: OM-4Ti 2/10 stop brighter, or just about what you might expect
to be the difference between f/3.5 and f/3.8.
As the mythbuster guys would say: BUSTED.
Walt
--
"Anything more than 500 yards from
the car just isn't photogenic." --
Edward Weston
-------------- Original message ----------------------
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxx>
> What you and Moose have said now seems to make perfect sense but I'm
> still curious about the reality. According to your arguments an f/4
> lens on a 6x6 camera should have approximately the same screen focusing
> brightness as an f/2 lens on 35mm. In fact, it should be brighter since
> the eyepiece doesn't have to magnify the image as much.
>
> Can someone with a 6x6 and 35mm verify this?
>
> Chuck Norcutt
>
> Dan Mitchell wrote:
> >
> > So there's 4 times as much light available on the mirror to be bounced
> > into the eyepiece, and so if the image I'm seeing is the same size to my
> > eye, it'll be 4 times as bright in the 120mm camera. (or it could be
> > twice as large in each direction and the same brightness).
> >
> > It doesn't really matter how large the focussing screen is, or how
> > much magnification happens between the focussing screen and my eye;
> > there's Z amount of light available bouncing off the mirror in the 35mm
> > camera, then there'll be 4Z that amount of light bouncing off the mirror
> > in the 120mm camera.
> >
> > What happens between mirror and eye is then the usual tradeoff between
> > image size and image brightness -- but the 120mm body has four times the
> > light available when making that tradeoff.
>
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