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Next PZ lens test report: Tokina AF 50-135mm f/2.8 AT-X Pro DX
Well I think the lens itself might have it's tolerances by means of rendering focus point(s) on the sensor side (at wide open). This might be because of the micro calibration errors on the optical elements' assembly or the lens mount thread's tickness, or special glass elements used (which might be effected by the temperature changes) etc... Actually when I consider all of these, I'm amazed how most of the lenses focus accurately (at wide open). Yes AF fine tune can be the cure, but it has some consequences also. After a large tuning adjustment, the lens might have problems with infinity/close focusing. Or what about the zoom lenses? Which FL to choose for fine tune? Or the distance of the chart used for AF fine tune, will you shoot subjects always from that distance?... Put all these in the same pot with a high resolution image sensor, ensuring 100% accurate AF in all cases, which can be viewed on 100% enlarged images might sound like a wishful thinking. But modern DSLRs and lenses do a very decent job here I think.

Regarding the green dot: That 1/3 dof statement you've mentioned does not look ok to me. First of all, dof does not have strict near/far limits. There's a transition zone (the OOF subjects get more blurred as they go away from the dof limits). How one can calculate a 1/3 dof range is unclear to me. Also I remember reading some statements in various forums telling that the range where the AF indicator says "sharp" is much wider than the dof of a fast wide angle lens at close focus. So if that's true, live view magified MF is your friend for such cases. Just check the dof table of Zeiss 35mm f/1.4 @f/1.4:

I don't think a modern DSLR's focus confirmation dot can handle such dof ranges at close focus.


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Next PZ lens test report: Tokina AF 50-135mm f/2.8 AT-X Pro DX - by PuxaVida - 07-24-2012, 07:09 AM

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