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| p.1 #1 · L lens copy variation oddities (very odd stuff) |
So I was trying multiple copies of some lenses and here are some odd results in one case:
At 70mm, lens copy 1 is sharper than copy 2 dead center frame, especially at f/2.8 wide open. Copy 1 also hits peak more quickly, since it has f/4 sharper than f/6.3 but copy 2 has f/6.3 sharper than f/4 (copy 1 has f/6.3 a bare trace sharper than f/6.3 on copy 2 so it's not that copy 2 is sharper at f/6.3 than copy 1). OK not SO weird, copy variation can exist, even in L lenses. If I focus on the edges copy 1 is also sharper, for the most part (at f/6.3, on one side only, copy 2, is a TRACE sharper than copy 1). Again, OK, so copy variation exists.
But here is the weird stuff, at 24mm I looked into how the rest of the scene looked too and not just as the focusing point.
At 24mm, copy 1 seems to be just a trace sharper than copy 2 in the center, both focused on object in the center. The object was a tree about mid-way deep into the scene, perhaps (best of a few live view focusing attempts was used). Now oddly, if I pan around the frame, other trees at various depths appear sharper with copy 2 than on copy 1, especially at f/2.8 where it is a VERY noticeable difference, at f/4 it is fairly noticeable, at f/8 a little bit noticeable. So copy 2 is sharper at the edges and corners right?
But wait, if I go and focus on an object at the edge or in a corner then I get sharper results on that object on the boundary with copy 1 than I do with copy 2! So now it seems like copy 1 is better at the edges and corners!
So it's like the two lenses are somehow placing the DOF differently or have different FC or something That might not be weird if it was two different lens designs but it is merely two different copies of the SAME lens!
What is going on
Copy 1 is basically as sharp or sharper when focused anywhere in the frame it seems at that object that is focused on, at 70mm center frame at f/2.8 it even beats copy 2 at f/4 (by f/6.3 they are very close). And the lower left corner at 24mm f/4 it is definitely sharper than copy 2 and a little bit so upper left corner 24mm f/4 and yet if I focus both on some tree mid-way into the scene in the center then copy 2 is almost as sharp on the tree that is focused on and the other trees, especially closer to edges, and super especially upper left quadrant, are a bit sharper with copy 2 than copy 1 at f/8 and very much so at f/2.8!
It's like copy 1 is a sharpness monster, whatever is exactly focused on is MAD sharp (well maybe not quite for far edges at 70mm, this lens model is OK there but nothing amazing) and yet has some sort of different and maybe odder field curvature (or maybe it has the normal FC) and yet can, for some scenarios at least, give real world results noticeably less sharp over the entire frame as a whole, depending upon where focus depth was place and where objects are in the scene. My vague impression is it might hold for more scenes than not, but I'm not 100% sure, especially if one gets into trying to find the ideal focusing placement for any given scene.
An interesting test would be to find the ideal depth to focus at for a given scene for each lens and then compare the two results and see if copy 1 doesn't manage to do better then than copy 2. I also wonder if on avg half scenes would fit copy 1 more easily and half copy 2 or if, in real world, the way the DOF works would make one fit natural scenes better much more often and if that would matter more than one copy being less sharp overall.
It seems to be easily to quickly get landscapes with extreme bottom corners, especially bottom left, 100% crisp with copy 1 but easier to get more distant stuff and especially the upper left and upper part to fit DOF with copy 2 perhaps
I will post samples later, but the differences in where DOF seems to be placed appear to be significant. I mean really easily noticeably different parts of the scene are in focus with one vs the other when both are focused on the same object. I know that can vary a little and sometimes a lot between different designs, but maybe it's actually more of a copy to copy thing than even a lens design thing
It makes it really hard to even figure out which lens copy is better in a practical sense. Maybe it would depend scene to scene. If I just focused on each part of a test chart with each and looked at the spot focused on, I'd pick copy 1 for sure and yet a quick scan over some real world scenes, focus placed on some central object almost makes copy 2 appear to be better, maybe even noticeably so once getting wider than f/8, at least on the wider to mid-range range. Then again on one shot copy 1 is crisp to depths on the near landscape corners and copy 2 is not.