A reminder for some memebers as to what the F stop is all about.

Started Jan 26, 2014 | Discussions thread
bobn2 Forum Pro • Posts: 62,183
Re: Agreed!

philosomatographer wrote:

I know what you were trying to achieve with your hypothetical scenario, but it is, of course, not realistic. With the smaller sensor, we are usually shooting at two stops less noisy ISO, because our lens is often two stops faster,

That is exactly it. If you can go two stops down in f-number (and lower ISO), the smaller sensor brings advantages of size and cost. So, that tends to limit the practical advantage of FF to wider than f/4 for zooms and wider than f/2.8 for primes, because you can't get the lenses at that range. There are some popular lenses where Four Thirds cannot go, like the Nikon 14-24/2.8 or 24 or 35/1.4 lenses but for the the bulk of brighter light photography for deeper DOF, there isn't a whole load of difference.

and often better in the optical department (because of telecentricity, and the fact that it's larger in relation to the sensor, and thus better-corrected).

I don't think telecentricity helps the optical department, in fact it makes it more difficult to correct the lens, but allowing the lens to be oversize in relation to the sensor certainly does help

In that scenario, the only thing that really matters is lens quality.

Then there is the case where you are shooting at base ISO on your 35mm sensor already - and there is no "two stops less noisy" ISO 25 setting on the small sensor. Then the small sensor can offer no match for the larger sensor, no matter what the origial poster seems to be claiming.

That is a point that the Four Thirds designers seem to have missed, with a base ISO of 25, the system would have matched that too.

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