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Archive 2015 · How to test crop body+500mm+1.4xTC AFMA without thermal effects?

  
 
kabraxcis
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p.1 #1 · p.1 #1 · How to test crop body+500mm+1.4xTC AFMA without thermal effects?


Hello, I am trying to AFMA my 500+1.4xTC on 7d2 and have found that it is either off because of thermal effects (I did this out of my window into the street on a sunny afternoon) or the combo just isn't sharp. I doubt it's the latter and would like to do my dot-tune method while getting rid of the thermal effect factor as much as possible.

Would a green, grassy area with no water suffice? I did it onto a building from a building with hot streets between the two points, which I am guessing lead to my AFMA's demise.

What targets do you generally use when doing AFMA on-site? I try to use park bulletin boards, is that what you would recommend?



Jul 27, 2015 at 10:41 AM
AmbientMike
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p.1 #2 · p.1 #2 · How to test crop body+500mm+1.4xTC AFMA without thermal effects?


Was the window open? I wouldn't recommend trying to test a tele (or any lens) through a window


Jul 27, 2015 at 10:46 AM
jcolwell
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p.1 #3 · p.1 #3 · How to test crop body+500mm+1.4xTC AFMA without thermal effects?


I test my 500/4L IS indoors at about 12.5m (40'), with and without extenders. Later, I do some spot checks outside at longer distances and it always seems to be OK.

I use the LensAlign II target. The camera is tethered to a notebook running EOS Utility. I achieve initial focus lock using the AF button on the camera (while looking through the OVF), and then go to LiveView on the notebook to evaluate the location of sharp focus, and make adjustments (+/- AFMA single steps), using the "<" and ">" LiveView focus controls in EOS Utility. I record the number of > or < steps (+ or -) as the AFMA value in the camera, and I'm done.



Jul 27, 2015 at 11:05 AM
Imagemaster
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p.1 #4 · p.1 #4 · How to test crop body+500mm+1.4xTC AFMA without thermal effects?


For zero chance of thermal effects, it is best to test within a vacuum.

Be sure to wear breathing apparatus.



Jul 27, 2015 at 02:34 PM
qc_mountain
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p.1 #5 · p.1 #5 · How to test crop body+500mm+1.4xTC AFMA without thermal effects?


For AFMA your lens you need 14-meters or 45.9-Feet of distance , grass is a good heat dissipator early in the morning the sun in your back avoid shadows on your target. Make sure you have a good target with a lot of contrast Like jcolwell said LensAlign II it is a good one, this should help you to AFMA your lens.

Francois



Jul 27, 2015 at 03:23 PM





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