Originally posted by Fogel70 APS-c- ISO 100, ƒ5.6, 1/50s
36x24- ISO 100, ƒ8, 1/50s
Both capture the same same image and same ISO noise performance can be measured on both for the same ISO.
Everyone happy?
The most common case were FF get a benefit and justifiy the better number is:
APS-c- ISO 100, ƒ5.6, 1/400s
36x24- ISO 50, ƒ8, 1/100s
The FF picture will have better quality, more dynamic range, more definition etc... The only practical issue is that to really see it you would need a 60" print and an high end FF with 36MP+.
Another case is:
APS-c- ISO 1600, ƒ/2, 1/50s
36x24- ISO 3200, ƒ/2.8, 1/50s
Noise is comparable but the FF guy can use an f/2.8 zoom (like a 70-200) while on APSC you'd need a fast prime. This is quite common case for shooting events (weddings...) and maybe the biggest reason for a pro to get an FF.
And of course ultimate shallow deph of field
APSC ISO 100 f/1.4 24mm
36x24 ISO 100 f/1.4 35mm
When you want to isolate a big subject with a WA, there always too much deph of field. If you can't use a tele instead (not enough working distance to have the whole,subject) or if you want the perspective rendering of a WA instead of a tele, then you need a fast WA. But that's a very specific use case.