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| p.1 #16 · New Sigma 18-35 f/1.8 lens (APS-C only) |
That is not correct. You can shoot at higher shutter speeds at the same ISO, but you will also get more noise at the same ISO than with a FF sensor. All other things being equal, you could just up the ISO by a stop for the FF sensor and shoot at the same speed without a noise penalty.
Equivalent lenses wil gather the same amount of light with the same DOF control for different sensor sizes, and that's what ultimately determines noise. That's the whole point of equivalence.
And it's a massively flawed argument that has no real bearing on image production, because the equivalence ONLY holds if the sensor technologies in the two compared cameras are identical. It's OK for determining similar depth of field requirements, but saying it's truly equivalent is far more false than it is true.
How do you compare lenses when one person is shooting on a 5D classic vs a D800? The D800 is 1-2 stops better at high ISO, so is an f/2.8 lens shot an a 5D really equivalent to an f/4.5 lens on the D800? No, of course not. Similarly, there are APS-C cameras out there right now that have image quality and noise characteristics very much in line with many full frame cameras of only a generation removed, and even very close to as good as some current gen cameras.
F/1.8 is f/1.8. Any noise considerations are a property of the format and sensor design, not the lens, and so while calculating the shallowest depth of field is a consideration, it's pretty much the ONLY way that the 'equivalent' aperture matters...as soon as you stop down a bit, any advantage is gone (for instance, if one needs the DOF offered by a lens at f/4 on full frame, the APS-C shooter can shoot 1-1/3 stops lower ISO and wider aperture.
This equivalence talk when used in this way isn't about comparing shallowest DOF, it's arguing format size (regardless of lens). I'm going to start coming out and shouting that a 24-70mm f/2.8 is really only an f/4.3 lens, since that's what it's 'equivalent' to on a Phase One IQ2. Who cares what depth of field is on a format that the person buying the lens ISN'T USING?
Edited on Apr 18, 2013 at 01:23 PM · View previous versions