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

Started Nov 1, 2010 | Discussions thread
nugat Contributing Member • Posts: 699
Re: Equivalent Values

seachicken2000 wrote:

f/1.7 = f/3.4 - same diaphragm diameter, gives the same DoF and exposure

A rose by any other name is still a chicken.

f number is the ratio of focal length and entrance pupil.

Entrance pupil is the projection of the diaphragm (iris, "aperture blades") diameter by all the glass in front of the iris. On different lenses the actual iris diameter can be projected to a different entrance pupil diameter.

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