# Canon AF



## 0ptics (Oct 21, 2012)

Hello so I'm a Nikon user but recently borrowed a Canon T2i/550D and a few lenses and I had a question about Canon's autofocus. One of the lenses that I'm borrowing is the *70-200mm f/4 (non-IS)* and I noticed that when I'm trying to focus on a subject the focus motor clicks back and forth. I don't know if it's the camera or the lens, but the distance scale keeps rapidly sliding from *30ft/10m* to *infinity*; it seems like the AF motor is glitching  creating a clicking sound as it slides back and forth. It isn't my lens so I don't know how old it is and I tried changing the settings on the T2i/550D and the lens but still nothing. I tried One Shot, AI Focus, and AI Servo, different metering modes, went through the menu settings but still the AF problem is still occurring  I then tried switching the *1.2m - infinity* to *3m** - infinity* but again still nothing works.

When I'm focusing on a single non-moving subject the glitch doesn't seem to occur; usually occurs when I'm trying to focus on something "disorganized/complex" (eg. bunch of leaves, branches, clouds that are spread out). I checked on Google and some other photographers with the 70-200mm had the same problem but couldn't find a true resolution/reason for the problem, but I do believe the problem is the 70-200mm USM because I tried other lens on the T2i/550D (10-22mm, 100mm macro, 18-55mm) and they all seems to work fine without any glitches/problem.

Any help would be much appreciated; again the 70-200mm isn't mine so unforgettably I can't send it in to Canon for a repair/checkup.

Thanks!
0ptics


----------



## rexbobcat (Oct 21, 2012)

Is it in good light. The going back and forth typically signals that it can't get focus either because of lack of contrast or difficult lighting conditions.


----------



## 0ptics (Oct 21, 2012)

rexbobcat said:


> Is it in good light. The going back and forth typically signals that it can't get focus either because of lack of contrast or difficult lighting conditions.



Ya it was definitely in good lighting/contrast; I even tested the same focal length/settings/subject/etc. with my Nikon 55-200mm and still the Canon 70-200mm glitched out. I really want to like the 70-200mm, its a beautiful piece of glass with an amazing build quality, but this problem is very unfortunate...


----------



## Dao (Oct 22, 2012)

My 700-200 f/4 does not make 'click' noise nor it have focus issue.  So would it be the lens you used has problem?


----------



## gsgary (Oct 22, 2012)

^ + 1


----------

