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Old Oct 29, 2006, 4:54 PM   #11
Join Date: Jun 2003
Location: Savannah, GA (USA)
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I'd make sure it's not user error by testing it in controlled conditons.

Use a tripod and test it, making sure you're selecting the correct focus point (either spot AF or selective AF picking it) and getting a lock (steady green light at bottom of viewfinder) before pressing the shutter the rest of the way down.

I'd use something like boxes with text on it, as Cope suggested, or books (as in my photo above). Although a less reflective surface compared to a shiny book cover is a good idea (reflective surfaces can sometimes fool AF systems).

Feel free to try the ruler type tests, too (those are relatively popular, but a books or something similar on a table seems a bit simpler to me). See my last post in this thread for an example of what I did to test mine.

If you've got your camera set to shoot without a lock, you may not have gotten one. Or you could have been reframing and throwing off your focus (or even leaning after locking focus). You don't need to lean much shooting with wider apertures to throw off your focus. ;-)

Reframing after a lock can also cause backfocus when DOF is shallow (your focus plain is not flat with most lenses and locking focus with the center point, then reframing will almost guarantee backfocus with some lenses and shooting distances).

It's best to use a tripod to see if the camera has a problem, checking it in more controlled conditions.

I'd leave it set to Single Shot (AF-S) versus Continuous (to make sure it's not switching targets on you), too.

Also, make sure it's just not something unique with the lighting (try it in different lightiing to make sure it's consistent). Sometimes, the temperature of the lighting can impact AF systems.
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Old Oct 30, 2006, 1:42 PM   #12
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Jim, I did few test shots of 45 degree scale with my 50/1.7 lens @f2....it looks good ...so I guesscamera and lensare OK.

It looks like this:
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Old Oct 30, 2006, 1:52 PM   #13
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One more thing....sorry about the WB, the shot was taken 2m from subject and cropped down. The light reflection from the desk caused the red tone...I know it is bad picture but thiswas quick test of AF.
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