At 03:46 PM 11/17/2010, Andrew Fildes wrote:
>I'm of the understanding that a f0.95 lens is a true f0.95
>regardless of sensor size - after all, if I put a medium format f2.8
>lens on a 35mm body, it's still f2.8 AFAIK. But there is a
>persistent theory that a 0.95 on an FT sensor is really equivalent
>to a true f1.7 or some such. I really don't understand the thinking
>behind this claim. Anyone care to opine on this and help me make
>sense of it before I make some claims in print.?
That claim primarily relates to apparent depth of field - a f/2.0 DZ
lens on 4/3 will give the same apparent depth of field as an f/4.0
lens on full-frame cameras, as you have to enlarge the 4/3 image more
to make a same-size print. This can be an advantage if you need
greater depth of field, a disadvantage if you want shallow depth of field.
This difference is mitigated somewhat in that the f/2.0 DZ lenses are
wonderful wide-open, while many full-frame fast lenses have to be
stopped down to f/4.0 to remove softness and light falloff in the corners.
For exposure, f/2.0 is f/2.0. I have yet to see a light meter that
asks your film/sensor size.
Some claim f/2.0 on 4/3 also acts like f/4.0 full-frame for image
noise, but there are far more variables that cause image noise than
sensor size, so I don't buy that argument compeltely.
Steve Troy
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