> I think you're confused. The size of the viewfinder isn't the size of
> the viewfinder lens you're looking into. The size of the viewfinder is
> the size of the screen which is close to the size of the film.
Oh, I know this much. And a 35mm 100/2 lens is letting in X amount of
light per mm2 of film, then if the 6x6 100/2 is letting in X amount of
light per mm2 of film as well, when you look at the total amount of
light over the entire film surface, there's just over 4 times as much
total light coming into the 120mm body.
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.
> I wouldn't doubt that someone has made a 90mm f/2 lens for a Hasselblad
> but I probably don't have enough money to buy one.
Well, the 100/2.2 I mentioned is only(!) $2,917 (and is sort of the
same as a 90/2, kinda, for these purposes at least). Heck, that even
gets you AF...
-- dan
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