alundeb wrote: Bifurcator wrote:
Why is it useful to talk about total number of photons in this way?
As an engineer, that is a very natural thing to do. Sorry
It is just that we hear from time to time that 75 mm f/2 on u43 gathers the same light as 150 mm f/2 on FF with the same ISO and shutter speed. When we try to explain whay that is wrong, the world explodes for those who think that a smaller camera gives a shutter speed advantage. Makten was once banned on another forum for explaining it.
It\'s not wrong tho. You\'ve created a confusion by talking about number photons over the surface of different sized sensors. A 75/2 on µ4/3 will indeed meter the same as a 150/2 on a FF. This is an unarguable fact. In fact if all lenses in a test group are perfect (without vignetting and etc) a 2mm f/2 lens will meter the same as 2000mm f/2 and on any camera you want to place it on. No one cares and no one can think about how many photons are required to make the image. We\'re photographers not photon counters.
Now as a function OF THE SENSOR SURFACE AREA (not yelling, just stressing the tense) one is using more information to form the image than the other. Thus what you have is sensor efficiency differential and nothing to do with the light gathering properties of a lens - which is what you actually hear people saying - and they\'re right.
See, I knew there was something hokey going on here.
Feb 15, 2012 at 10:38 AM
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