Fast Lenses and Mirrorless AF


Thoroughbred of Sin
Mar 31, 2019
One of the reasons I love my fast primes is they help my aging 70D focus in poor lighting.

Recently it occurred to wonder if this won't help mirrorless bodies at all: SLRs focus wide-open and close the aperture when you take the shot but think mirrorless preview at the set aperture so that you can see the DoF and features like Focus Peeking work. If I'm right then having a fast lens won't help unless you shoot wide-open (except for sharpness).

I know that the AF working range on mirrorless bodies tends to be a stop or two better than most SLRs but is that necessary to handle when you're focusing at 5.6 or smaller?


Jan 27, 2020
The current mirrorless cameras that either I own or have used (R, RP and Olympus cameras) focus wide open similar to the DSLRs. You do not see the DOF in the EVF. In poor lighting, the EVF brightens even more, so in poor lighting it is actually much easier to use the mirrorless EVF. The brightness of the EVF and VF can be adjusted separately. In every camera that I have, I always set the EVF to the brightest setting as this seems to replicate outdoor lighting best. Perhaps this is why the indoor brightness is exaggerated.

Kit Lens Jockey

Nov 12, 2016
I can confirm that the EOS R with an f1.2 prime on it focuses wide open, and it focuses amazingly well in low light when you do have this kind of a fast lens on it.

Even the 5D MkIV I used before the EOS R doesn't hold a candle to how quickly and accurately the EOS R can focus in low light, with both using the same prime lens.