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05-09-2010, 02:36 PM   #1
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New Pentax user old SDM problem?

So, after much deliberation and reading on this site (thanks for all the info), yesterday I took the plunge and picked up a K7 and a DA* 16-50. But I am worried that I have an SDM problem.
It was acting a little badly last evening, but it was dark inside so I let it go. Today, I was using it outside and it was not locking focus. I set it to centre point focus, single shot, and tried several targets in and around the yard, and it refused, and refused, and refused. Figuring I didn't know what I was doing, I switched lens's to my only other lens so far - the BIGMA. I was very surprised, and happy that the local store had a Pentax one in stock. I made no change to the camera other than the lens and tried to focus on the same things - it worked fine maybe not super fast, but it worked.
I tried the DA* 16-50 a few more times, sometimes it was fine, sometimes it worked ok for a while, then lost it. A couple times when it failed I tried quick shift focus thing when it wouldn’t lock and it would give me focus confirmation when I moved it into focus manually. Then after that the auto focus would work again. Set the camera down, half hour later it was a problem again. So it happens frequently, but it’s still intermittent.
From what I've read this sounds like the SDM failure problem. Before I return the lens to the store, since I've had the K7 and lens for less than 24 hours now, I thought I should ask here to see if I'm on the right track... Does this sound like the beginning of an SDM failure? Anything else I can do to confirm that it is, or prove it is not?

05-09-2010, 03:15 PM   #2
Ash
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This is a common issue.
And if it's what I'm thinking you're describing, it's not SDM failure or pre-failure.
It's simply the 16-50's SDM having trouble to lock focus at infinity or subjects further than about 10m.
You're not alone, my own copy does exactly the same. But I'm not sure if you're experiencing the issue at far away distances only, or if this happens at close focusing distances as well. If it is as I have it, you shouldn't be worried about SDM failure, focus can simply be locked with a slight turn toward infinity.
05-09-2010, 04:48 PM   #3
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Thanks Ash. I was focussing on varying distances, call it 3-15 meters. So I would say there were several targets within 10 meters that it would not focus on. But then when it works, it focuses fine on everything inlcuding targets over 10 meters.

Is this consistent with your problem?

I'll do some more testing as well, the last couple attempts it has focused on everything fine.
05-09-2010, 09:22 PM   #4
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I find that with both my DA wide angle zoom lenses, that using multi-point focus causes problems when they are set to wide. Centre point only gives me reliable results nearly all the time. There are some subjects that will give a lens a heart attack, but the wider the angle, the less the magnification of the subject, and the more confusing to the lens. Try centre point (or selected point) rather than letting the camera pick the focus point to use. It might help, and won't even cost you postage.

05-09-2010, 10:13 PM   #5
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I was using centre point, or at least switched to it and stayed there once it refused to focus, and still no good.

Of course it hasn't happened for a bit. It's been raining outside, but I've been trying it regularly inside, and it has been good. This morning it missed focus every second time I picked it up, but now it won't fail.

I bought it locally, so I'm thinking I should take it back, but I hate when I can't reproduce the problem.
05-09-2010, 10:58 PM   #6
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Obviously it doesn't work for you, have a refund asap, don't try to fool yourself. Seriously.
05-09-2010, 11:24 PM   #7
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QuoteOriginally posted by wlachan Quote
Obviously it doesn't work for you, have a refund asap, don't try to fool yourself. Seriously.
I agree completely. It is ridiculous that you have to try his hard to get basic AF to work reliably with a lens that costs this much money.

Dont accept this. There is nothing about the 16-50 that makes it worth these kinds of problems which appear to to common. If you can't get a good one, there are alternatives that are better anyway.
05-10-2010, 09:02 AM   #8
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+1 to send it back.
My first copy behaved just like this but only after 3 months.
It was eventually replaced by the local Pentax distributor.
So, it's not normal behavior.

05-10-2010, 09:05 AM   #9
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Thanks all. I will take it back, I'm not sure if I should try to get another copy or move on. I knew of problems with the lens, I guess I was hoping they were resolved, and maybe they are, and I just got a bad one...

I like the idea of a good sealed standard zoom, then I just need to pick out a good portrait, and possibly a macro and I'm set, at least for a while (I already have my long lens). I might have to re-evaluate the plan now.
05-10-2010, 09:11 AM   #10
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QuoteOriginally posted by gloop Quote
Thanks all. I will take it back, I'm not sure if I should try to get another copy or move on. I knew of problems with the lens, I guess I was hoping they were resolved, and maybe they are, and I just got a bad one...

I like the idea of a good sealed standard zoom, then I just need to pick out a good portrait, and possibly a macro and I'm set, at least for a while (I already have my long lens). I might have to re-evaluate the plan now.
The problem is that the idea of a good sealed standard zoom, and the DA* 16-50, are at odds with one another. Ask yourself honestly; how important is lens weather sealing to you? Is it worth the risk of SDM failure after warranty? Is it worth poor edge sharpness? Is it worth potential decentering? Is it worth AF problems like you, and Bart, and Ash (and who knows how many others) are experiencing?
05-10-2010, 09:11 AM   #11
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QuoteOriginally posted by gloop Quote
Thanks all. I will take it back, I'm not sure if I should try to get another copy or move on. I knew of problems with the lens, I guess I was hoping they were resolved, and maybe they are, and I just got a bad one...

I like the idea of a good sealed standard zoom, then I just need to pick out a good portrait, and possibly a macro and I'm set, at least for a while (I already have my long lens). I might have to re-evaluate the plan now.
If you still have it when you read this, have you tried the AF button instead of the shutter release half press? For some reason, I find that different lenses respond differently to the two options on my cameras. Might be worth a try, even if you intend to return the lens.

05-11-2010, 08:25 AM   #12
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Could not try the AF button, as the lens hasn't missed focus since I posted on here (which drives me crazy). I think I tried it while it was failing, but I can't say for certain.

I couldn't get to the store yesterday, but I'm still returning it today.
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