AF fine adjustment - how accurate can this be?

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Dericali Forum Member • Posts: 91
AF fine adjustment - how accurate can this be?

I'm spent some time calibrating all my lenses... but, I'm curious -

Firstly: What real world measurements do AF fine tuning + / - actually correspond to? Does this process mechanically move the sensor backwards or forwards, or does the compensation take place in the lens?

Secondly, AF fine tuning provides discrete units, but I'm assuming that when a lens is out, it is can be out by any amount from the baseline ... so you could test a lens that looks like it's about +2 or +3, when in 'reality' it's about +2.555555.... so how close you can get at home using your camera's menu is just an approximation, i.e you can assume at least +/- 0.25 if not +/- 0.5?

Thirdly, if I have a lens that is out by +2.555555 (working example here) and I send it into a a manufacturer, with the camera body, will they tune it so that is nearly entirely accurate? I mean will they be able to adjust it to a default setting using high tech equipment that is better than what I can manage at home?

Anyhow, please bear with me, I'm sure this level of accuracy is pretty negligible to most people, but I'm working on a project involving reflections in subjects' eyes so any additional accuracy helps. Please assume I'm talking about a prime lens for simplicity's sake.

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