Equivalent focal length for MFT lenses

Started Apr 12, 2013 | Discussions thread
Detail Man
Detail Man Forum Pro • Posts: 16,710
Re: Equivalent focal length for MFT lenses

KenBalbari wrote:

... there was a recent thread where a less experienced user seemed to be confused about whether getting closer to a subject would change the exposure, with the idea that the inverse square law should apply to the reflected light the same way it does to the lighting source.  Now everyone could tell him that this was wrong, and that changing the distance of the camera doesn't change the exposure.

What a piece of work that bloke was. The worst combination ever is dense as well as vitriolic.

But some of the explanations of why this is so were quite confusing.  I read through a couple and was still baffled as to why.

But the simple explanation that clicked for me was that if you move the camera position and keep the focal length the same, the size of the area captured changes so that the total light captured is the same, and if you change the focal length to capture the same scene, the aperture diameter changes to keep the total light (and the exposure) the same.  But if you change the distance of your strobe light from the scene, nothing automatically adjusts in the camera, so you have to change your exposure to account for the difference in total light being captured.

Puzzled a bit myself. Found this web-page (linked in the last post on the thread) to be helpful:


Regards, DM

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