Thu 17-Jan-13 01:05 AM | edited Thu 17-Jan-13 01:25 AM by sylvatica
Thanks for your advice.
Looking at those crops, it is hard for me not to be ballistic. But I am doing my best to keep cool.
Color of light: It is something that must be taken care of in phase detect system. This document from Canon ( http://www.canon.co.uk/Images/EOS%201DMKIV%20Technology%20Feature%20Guide_tcm14-721276.pdf ) shows on page 5 that their AF system is corrected for different wavelength. Nikon might do the same thing and I imagine that a camera not tuned correctly could be color dependent as far as AF is concerned. The most interesting thing is that even changing the color of the target makes a difference! Here are 8 shots in a row with the same amount of AF Fine Tune. The green line is where it should have focused and the pink line is where is has focused. As you can see, as soon as the target becomes red, it starts to front focus.
I've heard people complaining about the AF system to be unreliable after being "repaired". This could be an explanation.
Light intensity: I've done enough test to realize that an AF system never focuses exactly at the same point. Therefore, for all my tests, I use AFS single point, and I do 6 tests in a row, defocusing 3 times to infinity and 3 times to close range before asking the camera to focus. Everything is done on a tripod. And, the results are consistent. I've tried to change the color of light with exactly the same intensity of light (this is not the pictures I've posted) and the exact same problem was here.
I just can't beleive they dare to send you back a camera in that state.
For you camera, I have some questions: - Do you have lenses that you trust to be correctly calibrated, and are they fine for the central sensor at 0 ? - How big is the difference in between the central and the outer sensor? I mean, what is the difference in between the optimal AF Fine Tune for the sensors?