From DXOMark: More pixels offsets noise3

Started May 30, 2009 | Discussions thread
bobn2 Forum Pro • Posts: 61,122
Re: Yes, a bit tricky..

Steen Bay wrote:

bobn2 wrote:

Steen Bay wrote:

Yes, lots of logical traps to fall into. Assuming that bigger pixels
are always better, is a bit (just a bit) like assuming that bigger
sensors are always better, and forgetting that when shooting at the
same shutterspeed and DOF, all sensor sizes will have pretty much the
same IQ, because with the bigger sensor, you'll have to use a higher
ISO value and (f-number) to get the same DOF.

...and therein lies another trap. If you don't have a constraint on
the shutter speed (like a really good tripod and no movement in the
image) then in absolute terms you can gather more photons with the
bigger sensor, and get a better image.
The corollary of the James equivalence principle that is also
commonly misunderstood is that for a given output size, no format
has an advantage with respect to diffraction blurring. You get the
same blur for a given DoF with any format (and big pixels make it
worse, not better).


Like I just said in another thread.. It all comes down to our DOF
preferences, doesn't it? If you like the very shallow DOF that f/1,4

  • f/4 gives you on FF, then FF is the way to go, but if you prefer a

deeper, more 'normal' DOF, then FF won't necessarily give you better
IQ. If you're shooting at for example iso400, f/8 on FF, then a 2x
crop camera would give you just as good IQ at iso100, f/4.

I know, that with my kind of shooting, I would very rarely be able to
take advantage of the potential better IQ with FF, without
sacrificing some of the shutterspeed and DOF that I want. Actually
I'm more tempted by a camera like the Panasonic GH1, than I am by a
FF camera.

I don't quite agree with that. crop doesn't give any 'deeper' DoF than FF, since deep DoF is diffraction limited, and the diffraction limit is the same for any DoF, regardless of format. On the other hand, a larger sensor does give the absolute ability to use more photons to make the image at any DoF, so long as you are not shutter speed limited. If you're working at base ISO, and you are using f/11, 1/125 (quite good light) on crop, you need f/16 on FF. 1/90 will be needed for the same ISO, and the FF will give lower noise. In many cases, the difference between 1/125 and 1/90 is not worth bothering about, particularly with IS.

I have a FF camera and a crop DSLR. What I miss is a really compact system camera for travel, but one with a large enough sensor to give low noise and some DoF options. I have great hopes for the new Olympus Pen.

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