Originally posted by normhead As I said very little difference, and even that only in low light situations where you exceed the low light capability of the APS-c sensor but haven't exceeded the ability of the FF sensor. Given a real life DR of over 20 EV, one EV is a 5% advantage. That's about how often you can expect to have an FF advantage, unless you always shoot in exactly the right conditions. And for that stop of FF low light advantage, you lose one stop of DoF, so it works out pretty much even.
APS-C is a crop sensor. So are iphone sensors. I think a lot of the point for equivalence is for folks who are used to one format to figure out how to get similar framing with another format. Dynamic range and SNR considerations are secondary. I was one of those who was (and still am) more used to APS-C than full frame and so I used the formulas in reverse to figure out what lenses I needed to get certain framing.
My experience with full frame versus APS-C is that with portraits, it is nice to be able to shoot a little more shallow depth of field with full frame. With regard to dynamic range and SNR they are both pretty good at base iso, but go up much over that and full frame does have a significant advantage. Most folks aren't maximizing the dynamic range captured in an image and so APS-C or even micro four thirds would be more than enough for most situations.