Recently I purchased a brand new 70-200F2.8L IS lens to go with my 7D. I noticed while using it during my recent trip away that I wasn't hitting the focus anywhere near what I would expect. I was really disappointed with the sharpness of most of the photos. I tried all sorts of things with the camera focus setup all yielding similar results.
So after much reading about this, I went to the micro-adjust feature on the 7D. I was a little sceptical as to how much difference with would make and being a brand new lens (and rather expensive at that!) one could surely think that it should be pretty close. In the field I settled on a +15 setting which I was rather disturbed by.
Today I have finally had a chance to do some controlled tests. I set up the camera on a tripod square to target, IS off, live view for framing and using quick AF (so it focuses through the normal AF system). AF set to centre spot with the camera levelled using the inbuilt level. Metering was as constant as I could with apperture wide open (minimum depth of field). I used the inbuilt timer (with mirror lockup) so camera movement was non existent.
The camera was set up at >10m distance with focal length of 200mm.I then went through a sequence of shots starting with the micro-adjust at -20. I would manually turn the focus ring to infinity, then make the camera auto-focus. I took three shots on each setting until I had covered -20 -10 0 +10 and +20 on the micro-adjust.
I then did the same process with the camera at 100mm focal length and just over 5m distance to subject. I also did the same with my 24-105F4L lens at 30mm and 100mm.
After transferring to my computer I selected the sharpest image of each set up 3. I have then zoomed to 100%, cropped, labelled and assembled for you below.
As for the result, well lets say that the default setting of zero is bad and it is no wonder my photos were not coming out sharp. None of them are great especially when I compare to the 24-105mmF4L (I'll post those results here too when I get a chance to collate them but the shot at 0 is sharper than all these). Obviously the sweet spot might be between two of the points I have tested at. I will need to repeat the test at closer intervals in the range which is close to narrow down the sweet spot.
In summary as you can see, the micro-adjust makes a massive difference, especially on this lens. I'm keen to hear peoples feedback about this, I posted it here for two reasons, to show the difference micro-adjust can make, and to get advice on what I should do with this lens! I am really disappointed in it overall; the F4 version I had was MUCH sharper (hope you're enjoying that Alan!). I'm 99% sure I will send it in for service (I guess I will contact store I bought it from and see what they tell me). I'm concerned also that a +10 setting which looks best at 200mm is still poor at 100mm, so will it ever be right!?!!