I wonder if some of the lenses that have strong "field curvature" would cancel out the focus-recompose teqnique. if your focal plane was shaped like a " ( " for example, tilting the camera would all be on same focal plane. Sorry If i lost you, im sure a few people will see my point.
Possibly, but with a caveat.
The reason Focus+recompose doesn't work for a flat plane is because the distances change *if you rotate the camera around the nodal point of the lens*.
If, however, you rotate around your neck (which is what I would probably do), it is still possible (although *highly* unlikely), that you manage to still catch the focus where you want.
With a curved plane of focus (like on a fisheye, which afaik is a curved plane of focus bending around the lens), yes, there is the possibility to rotate around the nodal point and/or around your neck and keep the focus on the intended subject *if you know exactly how the plane is curved and can adjust yourself properly*.
Again, you've probably got just as much chance of catching the focus as with a flat plane.
But, there's one more problem. Lenses with curved planes of focus can also bend the other way, and as far as I know that's a lot more common. ie, focal point is 5m away in the centre of the image, and focus is at infinity on the edges. See the nice graphic here
. Focus on something in the centre, turn your head a bit, and suddenly they're even more oof than if you'd used a true flat-planar lens.
So yes, it is technically possible to focus/recompose with all of a flat plane, curved plane towards you, and a curved plane away from you. But unless you know the *exact* distances and *exact* way and shape that the plane of focus is curved, then any photos in focus using this technique will be purely coincidental (and a lucky chance).