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Topics - qwerty

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Lenses / State of large aperture lenses & digital cameras
« on: December 11, 2013, 11:22:11 AM »
Camera makers artificially boost the ISO (i.e. invisibly set the ISO and noise to be higher than what you told it to) when you are using apertures wider than f/2.8 because digital sensors don't capture the rays coming in at oblique angles (i.e. large relative angle with the normal vector) very well.  (This also has implications with respect to the amount of background blur; film will give better blur at large apertures.)  This means that larger apertures have less benefit than you would naively expect on digital cameras.

My question is whether newer lenses and sensors do better in this regard than older ones.  Does anyone have the means to test this?  If you have a "newer" fast lens, you just need to set the aperture, remove the lens (you need the lens attached to stop down the aperture), tape the contacts (to keep the camera from ISO-cheating), take a test shot, and repeat with a set of aperture/time combinations that should give the same exposure. (1)

I am particularly interested in the Sigma 35mm on a 5d iii, 1dx, or 6d (what with the talk of a new Canon 35mm and all)

(DxO measures the lens transmission in T-stops, but they only seem to do it wide open {at least as far as I can see with recent lenses}, so you can not tell the difference between light loss due to poor hemispherical integration at the sensor and other sources, e.g. reflections or manufacturers lying about the aperture.)

(1) One potential problem with this testing methodology is that the advertised aperture is usually different (read: faster) than the actual aperture.  I do not know if the apertures reported when stopped down are accurate in an absolute sense or based on number of stops from wide open.

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