f/1.8 on m4/3, ASP-C, FF; are they the same?

Started Nov 1, 2010 | Discussions thread
seachicken2000
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Re: Equivalent Values
In reply to Jonas B, Nov 3, 2010

f/1.7 = f/3.4 - same... exposure

I am throwing out the BS flag on this.

Yeah not so fast dispensing the BS flags. I've got too many of them already.

Exposure is the total amount of light captured by the sensor. The settings on the camera that you use to get the exposure are different.

Two cameras with the same angle of view and same diaphragm diameters, will capture the same amount of light. They will also have the same DoF.

For two cameras to be equivalent, they must capture the same image, photon for photon, and that means the exposure has to be the same for both.

A 20mm f/1.7 lens will capture 1/4 the number of photons (with a different DoF) than a 40mm f/1.7 on FF, and exactly the same number as a 40mm f/3.4 on FF (and with the same DoF).

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