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08-30-2012, 04:56 PM   #1
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K5 with Tamron 90mm- No AF at Infinity

I intended to shoot some pictures at Yankee Stadium (vs. Blue Jays) with my 18-250 Tamron mounted on the K5. When I got to the game I realized I mistakenly mounted the Tamron 90mm instead. Oh well, make do with what you've got..
However, I wasn't able to take pictures with the camera set on AF at infinity. I tried opening the aperture and various meter and focus setting. The hexagon focus icon was blinking. I could get focus at closer distances but not at home plate, which was further away.
Finally I switched over to manual focus and was able to get the shots.
I'm not sure what might be wrong here- lens, camera or user error. Any ideas as to what went wrong with AF?

08-30-2012, 05:00 PM   #2
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My Tamron 90 is old enough that there is no af. I just have to remember that when I use it, I have to turn the autofocus off on my *ist DS.
08-30-2012, 05:12 PM   #3
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What AF type? Single point?

Can you try again now? Just go outside, point at something really far away?
08-30-2012, 09:40 PM   #4
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I've had that behavior happen on an ultrawide when the AF micro adjustment was shifted a bit too much to the minus side. Seemed odd to me too, but after I correctly focus adjusted, it seemed to work fine.

08-30-2012, 11:33 PM   #5
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I was using single point AF at first but then I tried the green auto option (whatever it's referred to as?). I also tried changing the metering options.
None helped. I did have a Hoya Skylight (1B) filter attached.
I was sitting on the 3rd base side and noticed AF would lock in if I focused on a subject 100' feet away (eg. 3rd baseman) but no AF if the subject was the pitcher or batter.
08-31-2012, 12:56 AM   #6

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For focusing to infinity, your camera/lens combination probably needs a lens which can focus slightly further than infinity.

I've heard about this behaviour from other people before. It may change with temperature.
08-31-2012, 04:10 AM   #7
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I pointed the camera towards the sky and AF would not lock. I tried the same with the filter removed and still AF would not lock. I also tried with a -2 and then a +2 lens adjustment (menu #26 on C)- no AF lock.
Since I was shooting to infinity I can understand the AF not locking. In fact there weren't any significant clouds in the composition for contrast so the AF struggled I guess. However at the ballgame the batter or pitcher was only several hundred feet away, maybe 250'-350' or so? Certainly no where near "infinity". Still AF would not lock. I tried the various AF & metering adjustments by altering the switch positions on the camera body.
The lens takes excellent pictures whenever it does lock or if I manually focus. How does/can a lens focus beyond infinity? I don't understand the concept. Thanks.

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