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04-28-2013, 10:42 AM   #1
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Sudden loss of infinity focus: K5 w/ Tokina SD 28-70 3.4-4.5

Hi all,
A few days ago my K-5 stopped focusing properly to infinity with my Tokina 28-70mm AF lens. This lens has played just fine with this body up until now. I tested the issue with another lens and infinity focus was fine. I tried switching to manual focus, and when the lens was focused to infinity the camera would not confirm focus. The AF did successfully lock at short distances and with the lens in 'macro' mode, but attempting to focus on anything more than about 30-ish feet away resulted in the camera focusing out as far as possible and then displaying the blinking 'cannot obtain focus' hexagon. (i.e. there was no hunting; there was also plenty of light out.)

Fine AF adjust was initially set to -10 all, +2 this lens. I tested at -10/-10, 0/0, and +10/+10, and failed to obtain infinity focus at any combination of settings.

Is this likely to be a physical issue with the lens? I can't afford to replace this lens.

Thanks for any advice you can offer.

[edit]
I also tested the camera with one more lens, and can confirm that on 2 different lenses the infinity focus is fine. Whew.


Last edited by Sicariphus; 04-28-2013 at 11:08 AM.
04-28-2013, 11:13 AM   #2
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Interesting, I feel like I had similar problems yesterday with my DA 55-300mm. Sometimes it would appear to have trouble locking and when I got home an looked at my images they don't have the normal level of sharpness. I originally suspected that the softness might be because I forgot my lens hood but maybe there's more to it because it doesn't explain the locking trouble. I haven't had a chance to do any further investigation yet.
04-30-2013, 09:22 AM   #3
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Anyone else? I'm really scratching my head here.
04-30-2013, 10:50 AM   #4
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At infinity, a lens is closest to the sensor. "Something" is preventing the lens from fully retracting. I would start with the simple and carefully examine the mounts on both the body and the lens. For example, check for a loose screw that may hold the lens slightly further away for example.

My next step would be to double check some kind of crud isn't preventing the lens from fully raking end to end within the lens barrel. I purchased a used DA L 55-300 that must have had a grain of dust that vibrated into the racking mechanism. I thought I had been sold a bad lens, but some relatively strong blasts of air into the edge of the lens barrel along with movement must have dislodged it - it's been great since.

Finally, try running the camera's sensor cleaning. Your sensor may be slightly out of position and running the cleaning routine may put it back into place.

All of the above are of course guesses, but "something" is preventing the lens from getting as close to the sensor as needed for infinity focus.

05-06-2013, 12:20 PM   #5
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QuoteOriginally posted by JimJohnson Quote
At infinity, a lens is closest to the sensor. "Something" is preventing the lens from fully retracting. I would start with the simple and carefully examine the mounts on both the body and the lens. For example, check for a loose screw that may hold the lens slightly further away for example.

My next step would be to double check some kind of crud isn't preventing the lens from fully raking end to end within the lens barrel. I purchased a used DA L 55-300 that must have had a grain of dust that vibrated into the racking mechanism. I thought I had been sold a bad lens, but some relatively strong blasts of air into the edge of the lens barrel along with movement must have dislodged it - it's been great since.

Finally, try running the camera's sensor cleaning. Your sensor may be slightly out of position and running the cleaning routine may put it back into place.

All of the above are of course guesses, but "something" is preventing the lens from getting as close to the sensor as needed for infinity focus.
I'll be damned... That worked. Thanks!
05-06-2013, 12:52 PM   #6
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QuoteOriginally posted by Sicariphus Quote
I'll be damned... That worked. Thanks!
Great! But for the benefit of others .... what worked, playing with the lens or shaking the sensor?
05-06-2013, 12:56 PM   #7
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Compressed gas duster.
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