Originally posted by Mareket So making the sensor bigger doesn't make each pixel suddenly get more light, unless the size of each pixel is increased. So the exposure is still the same, as at f/2.8 1/100 ISO800 each pixel is receiving a certain amount of light, whether it's in APS-C or FF, so the total exposure is the same? The bigger sensor is getting more light yeah, but that doesn't mean each individual pixel gets more light unless they get bigger, so the overall exposure will be the same.
I'd like to see the day that people new to the topic ask the proper questions in order to understand this confusing topic. Rather than assuming their prior understanding
must be correct.
In order to help you reason about the topic: Assume two sensors, both say 24MP, one APS-C and one FF. Then the two images will be called "equivalent" if two corresponding pixels have collected the same number of photons. However, in order to achieve this, the ISO number on the larger sensor will be twice as high.
As a side effect, a larger sensor's pixel will typically not be "full" if the smaller sensor's pixel is. This translates in higher dynamic range for larger sensors. Not all silicon implementations make full use of this though, due to cost reasons.
In case the two sensors have pixels of equal size, i.e., the larger sensor has more pixels, then the same argument still holds true: because you scale noise down by downsizing an image.
Originally posted by Mareket Also bear in mind that FF will bring out the harsher vignetting/edge softness/CAs and all that of whatever lens you use.
The opposite is true. Another common misconception.
It is true that FF lenses have weaker corners and more vignetting/CA problems,
relative to the center. But that doesn't matter, esp. as FF lenses have a much sharper center and are stopped down more in equivalent images. You must compare corners and CA etc. between an APS-C lens and an equivalent FF lens. And then the equivalent FF lens wins hands down. It's just not a comparison done by any test report. You have to look up the individual figures and do the comparison yourself.
As a start, compare the Canon 70-200/4 L vs. the Pentax 50-135/2.8, in absolute LW/PH figures ...
(both lenses cost about the same, weight the same and are equivalent. But the FF lens has twice the border resolution at full aperture ... So, what corner sharpness are you talking about?
Originally posted by Mareket So people are hoping they can pay thousands of pounds/dollars/whatever more so they can have reduced DoF and for their lenses to be wider? Why?
I hope you understand the reasons are elsewhere.
It's not only a larger spectrum of lenses. Available lenses for FF should be cheaper (when equivalent) for physical reasons, or at a given price, they should be sharper. Beyond a given point in resolution, APS-C will become unaffordable (FT already passed this point with their crop-2 factor and APS-C will do soon too). And eventually, FF allows for more accurate AF operation for reasons I am too lazy to explain now.