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Re: [OM] Speed of lenses

Subject: Re: [OM] Speed of lenses
From: Andrew Fildes <afildes@xxxxxxxxxxxxxx>
Date: Sat, 7 Oct 2000 22:38:13 +1100
>Yes, and the film format difference is driven by the size of the image
>circle.  The 80mm f/2.8 Sekkor on my M645 is a much larger lens than the
>85mm f/2 Zuiko, even though it's slower by an entire stop.  That's because
>the image circle is bigger and must spread the light around a bigger film
>frame.  It's also why, if you look at large format lenses, they have a
>large diameter, are horridly expensive, and still incredibly slow compared
>to equivalent lenses for 35mm format.  They have huge image circles to cope
>with all the lens board and back adjustments.
>
>-- John
>

Hmmmm. How then do you explain the size of the 80/2.8 Planar on a
Rolleiflex? A lot of quite fast lenses on folders were TINY compared to
35mm lenses of equivalent speed. Surely the lack of focussing movements
can't explain it all, especially given the built in leaf shutter.
Andrew



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