Here is a first for me, a filter shifts the focus.
I have 70D and 70-200 IS 4 lens. I calibrated the AFMA to be +3 for the tele end, everything works fine.
I put a (cheap) filter on the lens and didn't think anything about it. Went to shoot some presentation on stage. I was about 50 feet from the stage. Used the lens at f4.0 200mm. After I went home and examined the photos, I could see that the camera was front focusing by about a foot. The microphone in front of the speaker was in perfect focus and sharp.
I figured that I need to calibrate the AFMA, so I setup a dummy head outside in front of a brick wall and the camera 50 feet away. First I focus in live view, turn the AF switch on the lens to MF. Can't find any AFMA setting that will give me focus confirmation. So I examine the photo taken with live view and I see that the wall is in focus, not the dummy. Try again, same result. At this point I figured that the camera and lens will have to go to Canon for some serious calibration.
For some reason I decided to remove the filter and try again. Now everything works perfectly, live view focus on the dummy and PDAF with AFMA of +3 focuses perfectly also.
Conclusion, this filter makes PDAF to front focus by about a foot, and DPAF back focus by a foot. Other then the shift in focus the images are sharp.
This is very weird.
I have 70D and 70-200 IS 4 lens. I calibrated the AFMA to be +3 for the tele end, everything works fine.
I put a (cheap) filter on the lens and didn't think anything about it. Went to shoot some presentation on stage. I was about 50 feet from the stage. Used the lens at f4.0 200mm. After I went home and examined the photos, I could see that the camera was front focusing by about a foot. The microphone in front of the speaker was in perfect focus and sharp.
I figured that I need to calibrate the AFMA, so I setup a dummy head outside in front of a brick wall and the camera 50 feet away. First I focus in live view, turn the AF switch on the lens to MF. Can't find any AFMA setting that will give me focus confirmation. So I examine the photo taken with live view and I see that the wall is in focus, not the dummy. Try again, same result. At this point I figured that the camera and lens will have to go to Canon for some serious calibration.
For some reason I decided to remove the filter and try again. Now everything works perfectly, live view focus on the dummy and PDAF with AFMA of +3 focuses perfectly also.
Conclusion, this filter makes PDAF to front focus by about a foot, and DPAF back focus by a foot. Other then the shift in focus the images are sharp.
This is very weird.