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06-21-2007, 03:51 PM   #1
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DA 16-45 focus lock problem

Hi, I have bought the 16-45 a month back and so far it seems a very sharp, very decent built lens with no problems at all (I don't see CA as a problem, I just remove it). However: sometimes I have focussing problems in wider angles (16-24).

The lens occasionally does not acquire focus lock even when I do point it at something that should be focussable (my kit lens was able to do it...).

If I zoom in to 45, acquire lock, zoom back out to 16 or whatever it does still have the lock and the pictures are sharp. So .. That's my workaround. I'm not sure if the lens should behave like this or that my copy is weird. It's just a new one tho so it sounds weird.

It only happens at the infinity setting. If I want to lock at anything within 2 meters it will lock instantly almost (very nice AF!). If I want to lock at something at infinity it won't acquire a lock and I am required to do the workaround as described above. Anyone else experiencing this problem? Is it normal?

06-21-2007, 05:54 PM   #2
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I have had this with a number of 3rd party lenses, and the Pentax-FA 28-105 3.2-4.5

Apparently it has something to do with not enough friction in the focusing mechanism. Pentax focuses then adjusts, on the adjustments there is not as much friction in the lens focus mechanism as the expects, it then throws past the focus point, tries to adjust back and throws past again, so on until it gives up..
06-22-2007, 01:57 AM   #3
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So... What do I do about it? If I can that is... :-)
06-22-2007, 04:51 AM   #4
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I haven't heard about it being common with NEWish lenses like the 16-45, so I think you would have a good chance of getting Pentax to repair it for free if under warranty. Even if it isn't take it to the Pentax service center in your state/country and ask kthem would it costs to fix!

06-22-2007, 07:14 AM   #5
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Take advantage of the quick-shift focusing to fix it yourself, or set it to manual focus and leave the focus ring on infinite - the infinite setting isn't far past 2m on the 16-45 anyway. I haven't had the problem like you describe but I don't think the focusing is anywhere near as accurate as my Sigma 70-200 f2.8.
06-26-2007, 05:47 AM   #6
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Mine behaves exactly the same. In AF mode, I have to AF at 45mm then zoom out to shoot, always. It tends to BF at the wide end (also on K100D that I tried). A lemon perhaps.
06-26-2007, 07:44 PM   #7
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QuoteOriginally posted by SupremeMoFo Quote
I haven't had the problem like you describe but I don't think the focusing is anywhere near as accurate as my Sigma 70-200 f2.8.
Nor have I - my 16-45 is a very well-behaved lens.

Jer
06-26-2007, 08:32 PM   #8
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having shot alot with the 16-45 for about 1 year I manual focus about 90% of the time. On autofocus I have yet to get a sharp photo, manual focus is a different story.

06-27-2007, 12:24 AM   #9
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QuoteOriginally posted by Donald Quote
having shot alot with the 16-45 for about 1 year I manual focus about 90% of the time. On autofocus I have yet to get a sharp photo, manual focus is a different story.
Hi there!

Well most of the time the focus is just put to infinity.

I did some recent 'tests' and now it seems I can get focus as long as I press the shutter halfway often enough. It'll get a lock most of the time after 3 times. It's also different if I pick a spot with hard contrast in it (a white/black border). It seems to be focussing more easily on that then on a plain white wall or a cloud. Instantly would be a good term

I just think it's strange that autofocus doesnt get a lock; it might not be sharp on AF (which isn't good imo as well :P) but let it at least lock I can always manually adjust the focus then with quickshift...
06-27-2007, 12:26 AM   #10
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QuoteOriginally posted by wlachan Quote
Mine behaves exactly the same. In AF mode, I have to AF at 45mm then zoom out to shoot, always. It tends to BF at the wide end (also on K100D that I tried). A lemon perhaps.
And you are not sending it back?

Is it still under warranty? The problem I have with sending it back is that I lose it for approx 7 weeks and in that time my entire holiday + shooting time is over :P

Also I am selling my 18-55 because the 16-45 has so much better image quality and I just love the 2mm... But that does mean I don't have a replacement when I send it back.
06-27-2007, 01:43 AM   #11
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QuoteOriginally posted by barendvl Quote
And you are not sending it back?

Is it still under warranty? The problem I have with sending it back is that I lose it for approx 7 weeks and in that time my entire holiday + shooting time is over :P

Also I am selling my 18-55 because the 16-45 has so much better image quality and I just love the 2mm... But that does mean I don't have a replacement when I send it back.

Sadly the DA16-45 I have is the 2nd sample from the same online dealer and the first one had serious misalignment. I suspect both suffered from poor packing for the transit as they were just sitting on one side of the box w/o protection at all. The lens was eventually sent to Japan for service but came back the same. I stripped it down recently and found nothing to be re-adjusted really but that the last 2 lens groups wobble when departed from 16mm. I believe it is this wobbleness that causes the BF as well as blurry pictures at 45mm (when shooting vertically, my copy at least). IMHO, if you can still exchange, do it. I am not optimistic that the service centre would be able to repair it.
06-27-2007, 03:52 AM   #12
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I have mailed the webstore to see if they can send me a replacement lens.

This way I still have a lens when I go on holidays and they can have it fixed in their own time.
06-27-2007, 04:38 AM   #13
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similar behaviour

QuoteOriginally posted by wlachan Quote
Mine behaves exactly the same. In AF mode, I have to AF at 45mm then zoom out to shoot, always. It tends to BF at the wide end (also on K100D that I tried). A lemon perhaps.
I used to have one and it would often fail to focus at full wide angle. It didn't hunt around particularly - it just didn't lock and beep. Even pointing it at a definite contrast often didn't work - but then it would suddenly lock maybe when an area with no detail was in the dead centre of the viewfinder. Which made me suspect that the central spot focusing area is in fact much wider than I thought. My other wide lenses do it too, but less. But they have other quirks - I guess it just means that very wide, precise AF is difficult for the camera and maybe not very important.

Tim
06-27-2007, 06:15 AM   #14
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16-45

I hear a lot of stuff about this lens, and I haven't experienced ANYTHING of what you're talking about. The AF beats my nikonian friends' SDM AF, and the CA, although I certainly see a lot of it in some focal lengths, it has never been a problem. Most zoom lenses I hav seen avhe been worse, because they have it all along the zoom range.

Maybe the production quality is not so good? At least I feel like only buying limited an DA/FA* lenses in the future, as it seems like the 16-45 next to the other at the dealer might be very different.
06-27-2007, 07:07 AM   #15
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As timo mentions at wider angles it doesn't seem to be so important simply because most of the time your focus is at infinity... That's what you mean, right timo?

And as far as I can tell the lens does have CA, however only if you pixelpeep. I'm not that much of a whiner about CA. I don't care how much CA a lens has. If you have a series of photo's that have it, you correct it in a few clicks in Lightroom... Or any other app.

The sharpness and contrast of this lens is remarkably good for its' price and it beats quite some, if not all lenses in its range of contenders.

Just compare the Tokina 16-50 AT-x Pro with the Pentax DA 16-45 over at Photozone. The results the 16-45 has over there basicly made my buy this lens and NOT the 16-50, which costs at least twice as much and is sometimes even worse in terms of sharpness (however only very very slightly). The 16-50 also exhibits alot of CA. For those that don't know, the Tokina will be optically the same as the Pentax DA* 16-50, or at least comparable.

Also, AFAIK the Pentax production quality checks are way better then for instance Sigmas' or Tamrons' production quality check.
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