Okay, help me out here RE: the True Focus concept.
Isn't off-center recompose a known and well documented issue? Isn't it why the 35mm DSLR makers employ movable multiple focus points, and have been striving to improve the sensitivity of the off-cented focus points?
The downside of the multiple focus points continues to be that they really are not out far enough from the center, don't always match where you want the focus point, and they still are not as sensitive as the center point ... and if solving all that were an easy task, wouldn't Canon/Nikon have done it already? Doesn't that indicate how difficult it would be to apply multiple focus points to Medium Format which is way farther away from the center?
I use the multiple focus points on all of my 35mm DSLRs for thousands of wedding shots a month, so I'm very fast at it. Yet, it is an imperfect solution at best. You have to wheel the focus point to the subject ... which may or may not be where you want it. So you get as close as you can then re-compose anyway ... only now at least it's closer in terms of distance. But, again, I still almost always have to re-compose. And subject movement or camera movement is the same either way when using single AF point.
This "True Focus" concept seems to solve those issues, at least in part, since it doesn't matter where the subject is in the composition ... you lock and re-compose without the time needed to wheel to a different focus point, then lock and re-compose like you do with a 35mm anyway. True Focus seems faster to me, and I dearly wish the 35mm DSLRs had this feature.
That it is now available in Medium Format with it's more shallow DOF seems pretty useful to me.
What I don't quite grasp is the role DOF plays in True Focus ... I get the differences between field-of-view of WA verses longer lenses, and made myself a "teaching aid" to show it ... where clearly the distance to off-center subject is greater with a WA field-of-view. On that chart are yellow lines that indicate distance ... what is missing is an overlay showing the effect of Depth-of-Field inherent with WA lenses verses longer lenses. I guess that would be possible, but you'd have to be pretty specific as which lenses, then map out DOF for each.
The other thing is flatness of plane which seems more critical an issue with WA than long lenses. Wouldn't hitting the off center subject exactly with your focus point aid in that?
Just wondering out loud, since I haven't actually tried True Focus and will reserve judgement. I just figure it can't hurt and I can focus as usual in some cases where the subject is close to the center.
-Marc