Equivalent focal length for MFT lenses

Started Apr 12, 2013 | Discussions thread
JeanPierre Martel Veteran Member • Posts: 3,054
Re: Equivalent focal length for MFT lenses

KenBalbari wrote:

Yes, that's what I said in the first place

Bravo. We are all saying the same thing. So sorry if I misunderstood your message.

If you change the focal length, you change the f-number.  Unless you fix the f-number instead, which means you are changing the aperture (which also changes the depth of field in the image).

Say that otherwise. I have no clue about what that means.

If you mean that 300mm m4/3 lens at F/2,8 = 600mm FF lens at F/5,6, that's true for the depth-of-field and for the angle-of-view only. But that's not the case for the brightness of the picture (the ISO being the same of course).

The same object shot with a 300mm m4/3 lens (on a m4/3 camera) and a 600mm FF lens (on a FF camera) will only look exposed the same way if the F stop number is the same on both lenses because that's the only way to get the same light density (same number of photons per mm2) to reach their respective sensor.

If the F stop number is set to F/5,6 on the FF lens (in order to have the same DOF), the image will be darker. So you have to set the ISO higher on the FF camera and consequently, lose some of the IQ advantage of the bigger sensor.

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