Why not a 12-35 F1.8 - F2.8?

Started Apr 2, 2014 | Discussions thread
JeanPierre Martel Veteran Member • Posts: 3,057
Re: Why not a 12-35 F1.8 - F2.8?

Anders W wrote:
Sure I can clarify. The basic facts are the following:
With respect to exposure, which refers to amount of light per area unit (e.g., per square millimeter) on the sensor, f/2.8 on MFT is equivalent too (has the same effect as) as f/2.8 on FF.

Exactly. Both at F/2,8, the image saved from the m4/3 sensor will be as bright as the image saved from the FF sensor. Because what counts for brightness (when the sensor technology is about the same) is the quantity of photons per mm2. A m4/3 lens at F/2,8 will allow exactly the same amount of photons per mm2 as a F/2,8 FF lens.

With respect to the total amount of light on the sensor (light per area unit times the number of such units on the sensor) as well as with respect to DoF and diffraction, f/2.8 on MFT is equivalent to (has the same effect as) f/5.6 on FF.

The total amount of light has to be twice when the sensor surface is twice bigger.

However the DoF is shallower on a FF camera. In order to get the same (larger) DoF as the one we have on a m4/3 camera, the FF user has to close the aperture and consequently, use higher ISO value. Doing so he won't necessary get more noise than the m4/3 user at F/2,8 but more noise than he would get using a lower ISO value on his camera.

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