Nikon screwdrive lens AF calibration

hidesert · Dec 20, 2014

Does anyone know how the lens itself is calibrated for autofocus? I have a 300mm f4 AF ED-IF that frontfocuses on all my cameras. I am unable to find a repair manual for this lens online, only for the AF-S version.

Al

summicron1 · Dec 20, 2014

autofocus typically is controlled by the camera computer, which reads contrasts in the image and adjusts the lens until they're sharp, or match, or something.

In any event, if your lens is not focusing properly, I am guessing it is not a user-serviceable problem, but am happy to be proven wrong.

benveniste · Dec 20, 2014

On lenses of this era it was sometimes possible for a technician to adjust the back focus distance by changing a spacer or washer inside the lens mount. I don't know specifically about the 300mm f/4 IF-ED; but that is possible on the newer 300mm AF-S model. But unless you count the "AF fine tune" feature of those other cameras, it's not a user-serviceable procedure.

AgX · Dec 20, 2014

But a back-focus mal-alignment would affect all, finder, sensor and film the same way.

It would not affect autofocus, except for possibly not reaching infinity-focus.

John Koehrer · Dec 21, 2014

^^^The OP's problem is Frontfocus.

It may be mechanical in that the AF limiter is a flexible circuit that allows for some adjustment via small slots in the flex. The slots adjust the stop point.

mdarnton · Dec 21, 2014

Nikon lenses with the electronic contact pins have chips in them programmed to handle the variations of each specific lens. They are not set up all the same, but calibrated individually. I did once have a link to a page that explained this, but darned if I can find it now. . . . I would imagine that this is something a Nikon authorized shop could easily do for you, though.

hidesert · Dec 21, 2014

Some more information on this lens: I sent it to APS, an authorized Nikon repair station and they state it checks out fine on their Nikon test equipment. It's frustrating because it front focuses by about the same amount on 6 different cameras, both digital and film. On one digital camera, a D7100 which has AF fine tune, a setting of +20 (the maximum adjustment) gets it very close. Focusing in Live View is perfect. But I want to use it on my film cameras, darn it! Since I know how to adjust a camera's autofocus my current solution is to take an extra F100 I have lying around and adjust the focus on this one camera. This makes that camera out of whack for every other lens I have except a Nikkor 180mm f2.8 ED AF. This kludge is why one needs to own many cameras

Chris Livsey · Dec 22, 2014

This link describes the programming of chips when added after the fact to Nikkors and the adjustment of back and forward focus.
http://pindelski.org/Photography/2012/03/17/adding-a-cpu-to-mf-nikkor-lenses-part-ii/
Presumably Nikon service does the same with the chip in the lens, but probably not using the shutter to do it!!

Nikon screwdrive lens AF calibration

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