[popo]

This thread is like a bad road crash. I know it is horrible but I can't stop looking...

 

The truth is that mirrorless cameras do not always nail focus. The truth is that I know of no DSLR photographer with that Reikan Focal, and I only read about it on Nikon forums. My guess is that the same people who like reading on DXO about DXO DR scores are the same who go about MFA-ing all their lenses all the time with stuff like that.

 

I'll be your first then. I bought FoCal early on so got it at a low price. To me, all focus systems (including mirrorless and MF too) have two errors: how close the average is to ideal, and how much variation there is around the average. FoCal helps DSLRs with the first, and can't help the 2nd part. At some point you get good enough and stop worrying about it.

 

At a practical level, I find I only need to AFMA fast short primes. It is a one time job then I can forget about it. And since I only really use fast primes on a full frame sensor, I only bother to do the 5D mk2 and neither of the 7Ds. Before FoCal, I had to do the poor man's LensAlign using a random target and a slanted tape measure next to it, manually tweaking values. FoCal now means I just press some buttons on a laptop and come back in 5 minutes instead.

 

There may or may not be some useful information from the produced reports. For example, when I got the 50 Art and ran it, it confirmed my suspicions the longitudinal colour wasn't as perfect as I'd like and ideally I'd have 3 AFMA values for each channel. Of course, that is impossible and is a feature of the lens design. But if I wanted to, I could bias the best focus for a particular part of the spectrum. I didn't bother in the end, since for normal use this is irrelevant. Another feature is it can give a sharpness rating for different aperture settings, if you're curious about that stuff. I think the author of the software is looking at putting even more lens analysis features in it, so over time it might becomes a poor man's Imatest.

 

For reasons unknown, I find the focus offset error is usually greater on APS-C sensors (higher pixel density revealing the error more?), and I've never had to adjust longer focal length lenses (150mm+). Even the Sigma 120-300 f/2.8 is fine without, but the 50mm f/1.4A needed a tweak. I suspect this is in part due to the error being related to any physical distance offset relative to the focal length, therefore the error effects are greater as focal length shortens. This error might grow faster than the effective DoF increases for shorter focal lengths, all else being equal. On paper, the DoF of the bigger lens is much smaller than the Art for a given subject distance.

 

On mirrorless systems, the average error should be pretty small with no significant offset. I have heard, but no experience, that some bodies may take a shortcut to increase speed over accuracy. Get it within the depth of field and stop. DSLRs likely do similar so not a big deal either way. For one shot AF, I find both DSLRs and mirrorless to be good enough. Still waiting for tracking improvements from the latter.

 

And finally, the EVF and OVF argument, I'd like to add a 3rd variable, if it is TTL or not. I thought the Fuji X100 would be fun so picked a used one up to play with. After using both the EVF and OVF modes, I found I actually didn't like the OVF! The problem for me was that I'm used to using a DSLR, so you can see an indication of the focus. As the OVF of the X100 wasn't TTL, you go no such feedback. So if I messed up the focus, I didn't notice until later. In this instance, EVF does give you the TTL view.

 

The possibility of adding extra overlay info to DSLR OVF has long been talked about, and I think would add value. I'd even love it if a crop body could offer >100% view, at least for FF lenses to get some extra situational visibility.