same f-number on different focal length - similar exposure? Locked

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JohnDope New Member • Posts: 2
same f-number on different focal length - similar exposure?

Hi,

It might sound like a trivial question for most of you, but I'm gonna ask anyway.

Let's say I have 2 lenses, 50mm and 100mm (FF, for argument's sake)

if I set my aperture the same on both lenses on the same camera, will the exposure be identical?

the f number is the ratio of the focal length to the diameter of the entrance pupil.

Hence, if I set e.g. f8 on both these lenses, the size of the entrance pupil will be different.

8=50/E.P --> E.P= 50/8.

and

8=100/E.P --> E.P=100/8

if the enterance pupil is not the same size, the amount of light (or the flux of photons) hitting the sensor would be different. Does that mean the exposure would be different as well?

Thanks.

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