Originally posted by asdf Note that a magenta tint would indicate a slight front focus. Green would indicate back focus.
I know what you're saying, but in this case, I think these show that the focal plane is actually curved.
These are all manual focus shots using LiveView at top magnification for focusing. The tripod was not moved between shots at same focal length, I just took the camera off to exchange lenses. I checked all shots and if they didn't look sharp, I tried a couple more times and I kept the sharpest. Zooms consistently exhibited softness off-center.
For all these shots there is no obvious tint in the center of the frame (which is where I focused on) - the tint starts showing as you look farther away from the center.
DA18-55@40 has some magenta tint towards center - I can't really notice any green.
M40 has a very slight green edge towards exterior, and even harder to notice magenta towards center. Hard to even notice these in that crop.
DA55-200@200 works on reverse - it has green towards interior and magenta towards the exterior of the frame.
K200 is like DA - green interior, magenta exterior
Because the tint is symmetric with respect to the center, I think this is because the focal plane is curved for most of these lenses. The M40 looks the best, but then again - that's a design derived from the Zeiss Tessar.
Here are 100% center crops from the same shots as above:
It's interesting to notice that in the center, the DA50-200 comes up as better than the K200. Otherwise, the M40 is a clear winner. As I said before, the difference is much smaller in the center - it's towards the outside of the shot that softness can be noticed more clearly.
And here is a new set of left and right crops showing the symmetric tint (they correspond to the same lenses as before):
The zooms seem to exhibit a much larger variation in sharpness across the frame.
And for the final bonus, some crops that show that mirror lenses don't have such bad resolution - these are the results I got from the Tokina 500mm - shot from quite a way from the target:
Not bad for resolution and pretty much no aberrations.