 Posted: Thu Aug 21, 2014 9:12 pm Post subject: |
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Posted: Thu Aug 21, 2014 9:12 pm Post subject: |
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bobcominitaly wrote:
@ LucisPictor There are a few things I don't quite get. In your blogpost, you assumed the Fuji 35 mm-1.4 has a 50 mm angle of view - which would be the case on FF. The lens itself still is a crop 35 mm 1.4, and will give you the image of a 50 mm lens on full frame, but still with the depth of field of a 35 mm 1.4 lens - which would be equivalent to that of a 50 mm 2.0 lens.
In fact this is where Ruben Kremer whom you referred to in your blogpost errs. He forgets to multiply the aperture by the crop factor, so assumes a 50 mm 1.8 lens on full frame will be equivalent to a 75 mm 1.8 lens on crop. Actually, it will be equivalent to a 75 mm 2.7 lens, Mounted it on a booster it will behave as a 50 mm 1.8 lens again - only on the crop camera, since the booster concentrates all the light of the lens on the crop field. But it does not add light - that would be physically impossible.
So your Pentax is a 50 mm 1.4 lens on a full frame camera and on a crop camera will have the properties of a 75 mm 2.0 lens. Once mounted on a booster it will be turned back into a 50 mm 1.4 lens, but with a crop field of view. Its depth of field will be that of a 50 mm 1.4 lens - which is smaller than a 35 mm 1.4 lens on crop, recalculated to be a 50 mm 2.0 lens on a full frame camera.
I have no explanation for the difference in T-stops with the Fuji and the booster-Pentax combination, but you might very well be right that it has to do with metering differences and differences in the way the lens apertures are calculated (rumor has it that Fuji is rather optimistic with its aperture figures).
I hope to find the time to repeat your experiment, though not with a 35mm 1.4 or a 56 mm 1.2 - they are beyond my means. Hopefully, the 18-55mm 2.8-4 will allow some conclusions, too. |
