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If +20 still shows confirmation this means the lens is 'extreme' front-focusing, so slightly defocus the image in LV by moving the focus toward infinity. For example, if -20 shows confirmation this means the lens is 'extreme' back-focusing, so slightly defocus the image in LV by moving the focus toward MFD. During the manual/LV AF step, slightly defocus the lens away from the extreme that still shows confirmation. Beyond the basic procedure there's actually a workaround when either end of the tuning range extends past +20 or -20, a workaround that will still let you discover the full tuning range (for example your theoretical -7 to -27 case). And the same has held true for most of the feedback I've received.īut of course there are always outliers. In the basic procedure the only requirement is that the confirmed AF range fits within the +/-20 tune scale, which was the case for the vast majority of bodies and lenses I used during the development and testing of the procedure. My personal stuff: ​photos/jngirbach/sets/ĭotTune has no reliance on the 'correct' MFA number being close to zero. I'm not paying Canon to calibrate a lens that works perfectly. But I can't tell for sure because I cannot see the dot turning off at values beyond -20.īut a lens that works perfectly with MFA near +20 or -20 is still a perfectly working lens.

Presumably.if I could do it the dot tune process would show me that the 'dot' lights up with MFA values between -7 and -27 on my 1D Mark IV, and so the correct MFA value for that lens is -17. If you are out near +20 or -20, then you cannot find the far extreme calibration that turns off the dot, so you cannot calculate the mean value to enter as the MFA. The problem with dot tune is that it only works when the 'correct' MFA number is relatively close to zero.

And the same lens is dead on with a +4 setting on my 5D Mark III. When I set it to -17 (for the 85L II for example) on my 1D Mark IV, then the lens focuses dead on. If the focus conformation does not work in that range then I would send that lens to canon.

Well, it has worked for all my lenses from the zeiss 21 to the Canon 600mm f4 l ii with 2x converter.