Is Full Frame sharper than APS-C?
After Way Too Much Time spent reading this thread, I still don't know
It's quite simple. A larger sensor/film will be less critical of the flaws in the lens infront of it. IE: it's make bad lenses not look so bad.
That's certainly true, but it's only a small part of the story.
The main reason has to do with simple geometry.
All cameras have lenses that project an image onto the sensor (/ film). And the dimensions of said sensor are fixed for said camera.
With rare exception, those sensors are much smaller than the final display size of the image that gets recorded.
Therefore, all photographic images get enlarged from their capture size on the sensor to their display size on the print or monitor.
The bigger the sensor, the less enlargement necessary.
It is unlikely you'll encounter a sharper photograph than a contact print made from an 8x10 view camera -- assuming, of course, all the usual caveats about lens quality and film chemistry and technique and the rest. It's certainly possible to screw it up, but, when done right, that's about as good as it gets. (One of those oversized Polaroids might be better...I've never seen one, so I don't know.)
In contrast to the lack of enlargement in an 8x10 print made from a view camera, an 8x10 print made from a 135 camera ("full frame") must be enlarged 7 times from the original image projected onto and captured by the sensor. Unless that original capture is at least 7 times sharper than the original capture with the view camera -- say, 7 times the linear pixel resolution of the sensor, or a lens that resolves 7 times as many line pairs, or whatever -- then the 8x10 print from the view camera is going to be sharper than the 8x10 print from the 135 camera.
Imagine you've got two square sensors. One is 1" x 1", the other 10" x 10". Both are divided into 1000 x 1000 pixel grids for a grand total of one megapickle on each sensor. Now, make a 10" x 10" print from each. The larger format is doing no magnification or interpolation, but the smaller format must enlarge each of its pixels 10 times to make the final print. Unless those original pixels on the smaller format are ten times better than the original pixels on the larger format, the larger format is going to win.
But...if you could make pixels ten times smaller and
ten times better for the smaller format, why not also for the larger format? Take a hundred of the smaller sensors and line them all up in a 10" x 10" grid, and this new composite sensor is going to absolutely smoke the other two by an insane margin.
The difference between APS-C and 135 isn't the 7 times of the difference between 135 and 8x10. It's only a factor of 1.6. It's not all that hard to come up with something 1.6 times better in the smaller format. Hell, just using a tripod can make that much difference, as can a decade of technological advances. It's because the difference between APS-C and 135 is so minor that we're having this discussion, that there's even a question in the first place. But that difference is
there, and it will always be there, even when the margins get blurry.
But, as a rough rule of thumb, if you're happy with a 15" x 22" print from an APS-C camera, you'll be equally happy with a 24" x 36" print from a 135 camera with comparable specs. Both represent a 25x enlargement from the original sensor capture. But, if you're happy with a 15" x 22" print from an APS-C camera, you're probably also going to find a 24" x 36" print from that same APS-C camera quite acceptable, because it's not going to be a whole lot softer than the print from the 135 camera. You'll probably be able to tell the difference if you look closely enough...but, again, if the image made from the APS-C was shot with good technique and the image made from the 135 camera wasn't, the APS-C shot will easily win.