Equivalent focal length for MFT lenses

Started Apr 12, 2013 | Discussions thread
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KenBalbari Regular Member • Posts: 276
Re: Equivalent focal length for MFT lenses

JeanPierre Martel wrote:

KenBalbari wrote:

The f-number does NOT tell you anything about the density of light or number of photons.  That is going to depend as well on the scene luminance and exposure time.

Please Ken, let's not complicate the discussion. We are talking about the same scene, shot in the same lightning conditions and same ISO setting but taken by two cameras -- m4/3 camera and a Full-frame.

What I'm saying is that the diameter of the opening of the iris will be different in a 600mm vs 12mm lens but the ratio of that opening vs the focal length will be the same when both are set at F/2,8 and when, of course, they are both m4/3 lenses.

Because the F stop number is a ratio and nothing but a ratio. It's not an absolute measurement in mm, for example.

Agree, but you also won't have equivalent images then, other than in angle of view and exposure.  Like I said in the first place, if you want to limit it to that, it's easier to simply talk about equivalent angle of view, and leave ISO and f-number out of it.

Otherwise, you end up misleading people into making the error the original poster made above.

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