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11-04-2017, 07:13 AM   #1
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DFA 28-105 can't reach infinity focus at 28mm

Hi everyone,

I bought a new DFA 28-105 a few months ago from B&H, and it's still excellent condition so it should be covered under the one year warranty.

The problem is that the lens isn't capable of reaching infinity focus at 28mm. I've turned on live view and slowly rotated the ring in the infinity focus direction, and it comes close to being sharp, but just doesn't quite get there before I reach the end of the focus range. It doesn't reach infinity with viewfinder autofocus, either.

At 35mm and beyond, it reaches infinity focus just fine. In general, this lens doesn't seem to have any other issues. No front/back focus, no softness, etc. It's sharp across the frame and throughout the zoom range.

I tested the lens carefully when I first received it, and I didn't have this issue in the beginning. Could there be a tiny piece of debris in there that is blocking the focusing element from reaching the correct position? Could there be a loose screw or something?

I know the best thing to do is to send it in for warranty service, but I'm currently outside of the US for a few months. Is there anything I could try to get infinity focus @ 28mm working again?

11-04-2017, 12:16 PM   #2
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You can try to use the fine focus adjustment. In K1 item 25 in the C settings menu.
11-04-2017, 12:35 PM   #3
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QuoteOriginally posted by Nuij Quote
You can try to use the fine focus adjustment. In K1 item 25 in the C settings menu.
That wouldn't affect whether or not infinity could be manually reached in live view, as in this scenario.

Hard to say what the problem could be in this case, but it might not be a bad idea to send the lens in while it's still covered by the warranty. Just make sure that the image is actually out of focus, rather than exhibiting the lens's natural softness, as it is possible to overzoom in live view.

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11-05-2017, 02:44 PM   #4
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Hmm, you know what, that's a good point about live view. Maybe I'll take a few more test shots and view them on a monitor to see if they're in focus. Otherwise I may just bite the bullet and send it in when I get home. Fortunately I'll still have some time left on the warranty.

Thanks for the replies!

11-14-2017, 12:14 PM   #5
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Same problem here, but unfortunately my lens doesn't have warranty left. I'll play with the fine adjustment and report back (if I don't forget). It's very annoying...
11-20-2017, 02:44 AM   #6
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Following up to the problem, I tested the lens on a different camera (K-50) and there it's able to focus just fine at infinity. Does anyone have a suggestion on what the reason could be?
01-04-2018, 01:38 AM   #7
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I'm mostly convinced I found the reason for the behavior, although I don't fully understand the logic behind it. I have a clear filter attached to the lens that had a tiny amount of dust on it. Cleaning the dust allowed the camera to focus to infinity at the 28mm-end. It seems the combination of the lens with a filter on the K-1 together with even a little amount of dust confuses the AF on the wide end... Alas, I'm happy the lens actually works fine.
01-07-2018, 05:50 AM   #8
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QuoteOriginally posted by antiguru Quote
I'm mostly convinced I found the reason for the behavior, although I don't fully understand the logic behind it. I have a clear filter attached to the lens that had a tiny amount of dust on it. Cleaning the dust allowed the camera to focus to infinity at the 28mm-end. It seems the combination of the lens with a filter on the K-1 together with even a little amount of dust confuses the AF on the wide end... Alas, I'm happy the lens actually works fine.
Good to hear you worked it out, it's one of my favorite lenses on the K-1.

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