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08-23-2011, 07:24 AM   #1
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DA 12-24 Focus problem

Hey, all. Just got a Da12-24, and I'm pretty stoked. It's my first "good" lens. Thing is, it won't autofocus properly. Unless the subject is like two feet away it just cranks over to infinity, makes a little electronic grunting noise and then won't lock focus, so the shutter won't fire and I get real frustrated. I've worked around this by using AFC, but I would still like to know- what the heck? I've never done the focus adjustment thing, would this be 'back focusing'?

08-23-2011, 08:38 AM   #2
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QuoteOriginally posted by ChatMechant Quote
Hey, all. Just got a Da12-24, and I'm pretty stoked. It's my first "good" lens. Thing is, it won't autofocus properly. Unless the subject is like two feet away it just cranks over to infinity, makes a little electronic grunting noise and then won't lock focus, so the shutter won't fire and I get real frustrated. I've worked around this by using AFC, but I would still like to know- what the heck? I've never done the focus adjustment thing, would this be 'back focusing'?
Back focusing, or Front focusing for that matter are exactly what they imply. BF is when your camera locks focus but the true focus point is Behind what you are supposedly focused on. The exact opposite is true for Front Focusing.

A few more details of what you are doing might help troubleshoot your problem. What are you trying to take pictures of, which camera are you using (shouldn't matter), etc. You should certainly be able to focus further away than a couple feet. Have you tried going to MF and just using the focus ring just to make sure the lens will focus at all?

08-24-2011, 07:33 AM   #3
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Thanks for the reply. Yes, I've done the manual focus thing quite a bit and the lens itself focuses fine that way, scary sharp. It's also fine in AFC, though the focus indicator is still flashing indicating a lack of focus lock, but at least the shutter will fire.
It does this about 75% of the time, so sometimes it works fine. It's usually when I'm just taking general snapshots, indoors or out. I'm using it on a k-7. It feels like maybe the camera is telling the lens to focus past infinity, which is impossible for the lens to do, so it never tells the camera that the focus is locked. Sound right?
08-24-2011, 08:34 AM   #4
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I actually haven't done a lot of distance shooting with mine. My K7 is long gone but with either camera I've had it on, I do note however that at the 12mm end, it struggles to lock focus or even find anything to focus on, at a distance. I think in that case, it may just be the nature of the beast. That is, what the camera is aiming at is so small compared to the AF area that there is virtually no contrast for it to sense. Even with a manual 28mm lens, far distance is sometimes hard to lock on the K7 IIRC. If I'm not mistaken, these DA lenses WILL focus past 'infinity' slightly and then re-correct. I'll have to dig mine out and give it a run on the K5 (it's barely been on that camera) but I'm pretty satisfied with my copy.



08-24-2011, 03:39 PM   #5
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QuoteOriginally posted by ChatMechant Quote
Thanks for the reply. Yes, I've done the manual focus thing quite a bit and the lens itself focuses fine that way, scary sharp. It's also fine in AFC, though the focus indicator is still flashing indicating a lack of focus lock, but at least the shutter will fire.
It does this about 75% of the time, so sometimes it works fine. It's usually when I'm just taking general snapshots, indoors or out. I'm using it on a k-7. It feels like maybe the camera is telling the lens to focus past infinity, which is impossible for the lens to do, so it never tells the camera that the focus is locked. Sound right?
It's obvious to me you have a faulty lens. Just send it back, or turn it in for a fix, whatever you have to do.
08-24-2011, 07:22 PM   #6
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Does it behave the same at 12mm and 24mm and everywhere else?

Paul
08-24-2011, 09:21 PM   #7
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QuoteQuote:
I do note however that at the 12mm end, it struggles to lock focus or even find anything to focus on, at a distance. I think in that case, it may just be the nature of the beast.
I don't recall ever having that problem with my "beast" - which I love.

Get replacement/service and see if that cures it. It is worth getting a working lens.
08-24-2011, 10:46 PM   #8
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My memory is playing tricks on me. I took it out for a minute last night (in response to this thread) and tried it near and far at 12mm and 24mm. I could not repeat the OPs problem with AF on my copy on the K5.



08-25-2011, 07:38 AM   #9
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I'll have to try it at 24 and see. I sure hope it isn't faulty, since I bought used...... twitch and specialK, I'll just be over here pretending I didn't read your posts.
Ah well, the photos do look good for now.
08-25-2011, 06:48 PM   #10
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I feel for you! Not a fun happy situation.

If you can MF the lens at a subject any distance from you the problem is minor (relative). CRIS Camera in Arizona (Pentax official repair center) is good and not as expensive as you may think. I would go to there web site if your interested. To replace the front group of my Sigma 17-70mm f/2.8-4.5 macro (3 lens bounded into a large front group) and shim the front for proper infinity focus (yes some lens use shims to set infinity focus) clean and set all adjustments to factory spec was $200 USA. The lens works perfect and came back like new. Not bad IMO.

Just in case... do clean the contacts!
08-26-2011, 08:13 AM   #11
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just an update: futzing around with focus adjustment yesterday, giving it a +8 seemed to have fixed the problem. time will tell.
thanks all.
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