Possibly moving to full-frame mirrorless from m4/3’s

Started 11 months ago | Discussions thread
ZapperVT Senior Member • Posts: 1,139
Re: Two quick and easy reasons

avalvo wrote:

- Yes, lenses on FF are getting smaller. But, that is only if you are comparing the slower FF lenses, say a 50mm 1.8 to say a 25mm Oly 1.2. They are about the same size, but the Oly is still a faster lens and can be shot at 1.2.

f/1.2 in M43 is equivalent to f/2.4 on FF. Or, f/1.8 on FF is equivalent to f/0.9 on M43.  Functionally, the FF f/1.8 has a one stop advantage over the M43 f/1.2.

If you shoot with at 25mm f/1.2 on M43 FF and 50mm f/2.4 , with the same shutter speed and two stops faster ISO on FF,  you will have images that are very close in field of view, depth of field, motion blur, and image quality.  This is because for the same f number, the diameter of the entrance pupil scales with the crop factor.  It is twice as big for full frame, letting in 4 times as much light at the same f number.  If you go to f/1.8 on FF, you have an image with a depth of field one stop smaller and an IQ potentially one stop higher than possible with f/1.2 on M43.

You may object that in terms of exposure, f/1.2 is still f/1.2, and you would have to use a slower shutter speed or higher ISO on the FF f/1.8 lens to get the same exposure wide open.  That is part of the equivalency.  If you shoot at the same shutter speed and wide open with both lenses, you will have to increase the ISO by 1 stop on FF to get the correct exposure.  But a FF sensor has a two stop advantage in noise vs IQ, so you still end up with a 1 stop advantage in IQ on the FF system.

Source:  Here's an article  on equivalency by one expert.

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