Accurate (and fast) focusing with manual lenses like Zeiss (zf2) and other CPU lenses

Started Dec 7, 2012 | Discussions thread
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inasir1971
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Accurate (and fast) focusing with manual lenses like Zeiss (zf2) and other CPU lenses
Dec 7, 2012

This post details how to manually focus CPU lenses using the in viewfinder indicators with bodies such as the D800/E, D4 and presumably others that support AF Fine Tuning. With non-CPU lenses like AIs lenses, Nikons do not support influencing the AF indicators with fine tuning - unfortunately, it's just a matter of luck whether your particular body's indicators line up with your particular copy of the lens.

Please see my notes below on the Nikon AF system - one can consistently achieve accurate focus easily using the focus indicators. I use a number of Zeiss including the 35/1.4, and 100/2 and have no difficulty focusing them wide open even using the indicators as described.

* there are only two deterministic events in the AF system - the transition points into and out of the AF zone of focus - where the AF system deems focus to be achieved.
* with fast lenses (f/2 or faster) this AF zone is actually wider than the depth of field, let alone the zone of sharpest focus. Therefore, when using a fast lens (in MF mode) it is possible without changing anything other than the focus ring position to take a shot which is front focused, in focus, and back focused all which the AF system indicate as being 'in focus'. The 'green dot' alone cannot be used to indicate focus.
* the AF system simply seems to place focus somewhere within this 'AF zone' leading to incorrect focus with fast lenses.
* with manual lenses (such as Zeiss zf2) it is possible to skew the AF fine tuning value so that one of the two deterministic events mentioned above in the AF (I chose the transition into the AF zone turning from camera) falls sufficiently within the 'AF zone' so that it can reasonably consistently indicate sharp focus.
* with AF lenses, the best that can be achieved is to fine tune the lens so that front focus occurs equally as often as back focus. This can further be helped by using AF-C so that the system hunts within the AF zone and success rate is increased.

This of course means finding out the AF tuning values for each zf2 lens.

BTW Nikons can only store the value for one zf2 lens so when you mount another zf2 lens you will need to enter the value for the lens being used - so write down the values for each of you lenses. Also, Voigtlanders share the same memory spot as zf2 lenses. (D800/E, D4)

Nikon D4 Nikon D800
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