> But that’s not the same thing as saying a larger sensor is better… you could have just used a lens with a larger physical aperture in the first place. You don’t need a larger sensor to do that.
Most optical aberrations increase with high powers of the f-number so it's highly undesirable to make ultra-fast lenses, so it quite quickly becomes cheaper to use a larger sensor with a slower f-number. Try matching a jellybean 85/2 lens on a full-frame sensor on e.g. MFT. It's going to be rather expensive. Then try matching a 85/1.4 or 85/1.2 (nowadays not uncommon) lens and you find yourself at "that's not physically possible".
Coincidentally, full-frame sensors can be made from just two stitched exposures on a regular chip stepper, so they're sort of the largest sensor size before cost explodes. Meanwhile S35/APS-C offers some real cost savings (single exposure).
Most optical aberrations increase with high powers of the f-number so it's highly undesirable to make ultra-fast lenses, so it quite quickly becomes cheaper to use a larger sensor with a slower f-number. Try matching a jellybean 85/2 lens on a full-frame sensor on e.g. MFT. It's going to be rather expensive. Then try matching a 85/1.4 or 85/1.2 (nowadays not uncommon) lens and you find yourself at "that's not physically possible".
Coincidentally, full-frame sensors can be made from just two stitched exposures on a regular chip stepper, so they're sort of the largest sensor size before cost explodes. Meanwhile S35/APS-C offers some real cost savings (single exposure).