on 7/31/01 8:59 AM, Tris Schuler at tristanjohn@xxxxxxxxxxxxxx wrote:
> Not sure what you mean by "least" amount of glass. Other things being equal
> the faster the lens is the more glass it will have in order to allow more
> light to get in. There's no reason the 40mm f2 could not be an f1.2, though
> with cost in terms of its size and weight--if that lens were an f1.2 it
> would come to us looking an awful lot like the 50/2.
>
> Tris
>
I think you have to factor in the coverage area (image circle) in relation
to the focal length and maximum aperture. The Zuiko 42mm/1.2 for Pen F is
what I'm thinking of. For a long time optic designers made the faster lenses
slightly longer than the slower... my Dad's 1966 Minolta SRT-101 had a
58mm/1.4 Rokkor, the slower lens was a 55mm/1.7 (I think). The Pen F lenses
go from 38mm/1.8 to 40mm/1.4 to 42mm/1.2 though I don't know why this is so.
Sort of related question I have... if the lens is say a 90mm/2.0 does that
mean that the actual span across the aperture blades wide open is 45mm
(clear diameter)? Is that why the 100/2.0 is so fat compared with the
100/2.8?
--
Jim Brokaw
OM-1's, -2's, -4's, (no -3's yet) and no OM-oney...
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