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I wonder what exactly is the calibration of a camera body and a particular lens. I know the effect, but how it is achieved?


I recently bought 80-200 (the two-ring version), I was waiting for too long to get this lens and respectively I was very upset to have to return it back because of backfocusing issue (a lot users have experienced this bad effect of this particular combination).

I was wondering if I should give the camera body and the lens for calibration, as I didn't want to return the lens and wait for another one to try, but I gave it up. The reason for this is: I don't know what exactly is the calibration. My concerns were: I have other lenses, I don't have this issue with them (I actually do, with most of them, but I fixed that using the AF fine tune, while this didn't help for the 80-200) and I didn't want to risk adding similar problem with them, too (like frontfocus, for example).

Related to:
* Does Nikon D7000 exhibit particular backfocusing problems?
* Is there a reason to avoid the Nikon 80-200 f/2.8 on a Nikon D7000?

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3 Answers 3

up vote 1 down vote accepted

If you're asking so you can do it yourself, sorry but you're out of luck.

The following only applies to DSLR cameras.

When adjusting lenses, collimators are used and can cost tens of thousands of dollars. They are finely tuned instruments.

A collimator optically emulates infinity (over 100 meters or so) and come in different sizes. It shines light through it and has a star (or siemens) chart at the end of it. Generally, the lens is mounted onto a movable mount can connected to a computer. You move it to the wide end and it'll attempt to auto-focus. You move the mount, to the nano-meter, and input the value. It'll do this a few times and then you do it at the tele end. Depending on the lens, you'll have to move it to a particular focal length. It'll average out the values and change the paramters on the lenses mainboard. If it's really bad, it will need to spacers of different sizes changed underneath the mount.

In the case of bodies, the same thing. There might be a master lens and you set up charts according to specifications. Sometimes it will need an X,Y mount and you'll move the body up/down, left/right according the the points it needs.

Now, if it's really bad, the spacers between the image sensor and body will need to be changed. Because it uses phase detection, the sensor is active when the mirror is down (might have time to do a diagram later). This is when it focuses, but when the mirror is up, it takes the photo. This is where it still could be focusing perfectly fine but the image sensor is misaligned. Spacers are as narrow as 10 micro-meters to align the image sensor.

In your case, it's probably just the lens. But, lenses and bodies can be adjusted and calibrated to match.

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They will most likely just adjust the lens, but use the camera body to judge how much to the lens needs adjusting. As a result your other lenses ought to carry on working fine.

In terms of what they can actually do to calibrate the lens, then it will vary depending on the lens but in most cases there will be a position sensor in the lens which detects where the focusing mechanism is and feeds this back to the camera. There will also probably be a lookup table in the lens firmware which stores how long to activate the motor for, depending on the focus instructions sent by the camera body. So it may be a purely mechanical solution (adjust position sensor) or a purely software solution (update lens firmware) or both.

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Sounds reasonable, but this doesn't actually answer my question, it's more like an advice on the details part of my post (with the smaller font). Thanks anyway. –  Kiril Kirov Nov 25 '13 at 13:40
    
@KirilKirov answer updated! –  Matt Grum Nov 27 '13 at 10:19
    
Not sure how many adjustments you've done but certainly for the case of Olympus E series DSLRs, the phase sensor is fixed and can not be adjusted. Only the image sensor can be mechanically adjusted. It is not purely mechanical or software (electronically adjusted parameters). It can be both if it's severe. –  BBking Nov 27 '13 at 23:42

Before you send your camaera and lens for calibration, you might try AF fine tune yourself. Please see: https://nikoneurope-en.custhelp.com/app/answers/detail/a_id/51633

You might also try the 'green dot' technique: http://www.dpreview.com/forums/post/50774257

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If you read my question more carefully, you'll see that I tried AF fine tune, but it didn't help :/ –  Kiril Kirov Nov 25 '13 at 13:39

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