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07-25-2009, 04:51 AM   #1
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DA 12-24 back-focus problem

The other day I got my second copy of the DA 12-24, after I returned the first copy due to an extreme back focus. Unfortunately, the second copy still has a back-focus, if not quite as extreme as with the first lens.

To put it into perspective, I have to dial in +110 in the Debug Menu of my K10D to get the focus spot on. (On the previous copy I needed +300!) Having said that, such a degree of back focus is mostly noticed at close-up distances.

I also would like to point out that the body is not the problem. I have a DS, as well, and on both DS and K10 I need to dial in +40 in the debug menu to get the focus spot on with my other AF lenses. On the DS I need +100 for the DA 12-24.

Among other tests I used this free focus test chart: Nikon D70 Focus Chart

I set the lens to 24mm f/4, roughly taking the photos at a 45 degree angle. The subject distance was such that the A4 focus chart almost filled the viewfinder, so I was pretty close.

I know that at more usual subject distances (landscape, architecture etc.) such a degree of back focus might not play a role, at all. But I still cannot feel being annoyed that a misaligned copy of the DA 12-24 seems to be the rule rather than the exception.

I am also wondering if I should return this copy, as well, or if it is just an "average" copy of a DA 12-24, so that I should put up with it or maybe send it in after the summer for servicing.

What are your experiences with your DA 12-24? Have you ever tested it for focus accuracy at close ranges?

Thanks in advance for your feedback
gattofix

07-25-2009, 08:25 AM   #2
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gattofix, I sympathize with your situation. Like most people I can only speak from personal experience with a single DA 12-24mm lens that I've owned for two years.

It has been tack sharp at all focal lengths on the DS, K10D, and D20D bodies that I've owned. I've tested the AF on the K20D with zero issues. If this lens had consistent manufacturing issues we would have known about it by now. Most likely you've run into just bad luck and a third lens will work.

That said, intuitively (which has nada to do with evidence, rational thought, and your findings) I'm feeling that your testing is flawed somehow (I use the same chart and methods). I'd reset the K10D AF to close to normal (whatever that is) and then go out to shoot reality. Then publish here your results.

M
07-25-2009, 10:57 AM   #3
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Real Life Shots

Thanks for the Feedback, Miguel, much appreciated.

I have just done some real-life shots.

Before I get round to converting them to jpegs and posting them, how big can an attached photo be here? I have not found the answer to this, there do not seem to be any guidelines or faqs, are there?

I reset the camera to +40 (from previously +100). Just talking about the autofocusing, not picture quality, the result is the same as with the first copy I got, just not as severe: sometimes the lens goes "past infinity" (it has to be in the middle of the infinity symbol, I have been told). On these occasions this results in a focusing error (blinking symbol). When I had the AF correction set to +100, this never happened. So apart from the IQ the back focusing seems to be proven.

The body cannot be at fault, because my DS shows exactly the same behaviour with this lens.

gattofix
07-25-2009, 12:56 PM   #4
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Excuse the obvious stupid question, but it needs to be asked for the record: Is your diopter adjusted properly?

M

07-25-2009, 04:25 PM   #5
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Diopter?!

You mean the adjustment if one is short-sighted? What does that matter if I don't focus manually using eyesight?

gattofix
07-26-2009, 05:16 PM   #6
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Real Life Shots

Here are some real life shots - as I don't have a pbase of flickr pro account, please download the photos:

http://sd2.1und1.de/qxclient/?username=@nonymous&path=DA12-24-K10D-test%20sh...051AFDC6C2C2B9

Do "select all" with control+A and then right-clicking, select "Speichern unter" (save as)

I find these hard to judge without comparing the shots to shots of another lens. Having said that, I also did some "newspaper" shots (subject distance about 1m), and did the same with my 18-55 II at both 18mm and 24mm with the result that the 18-55 II was noticeably sharper, especially towards the edges. And I don't believe this can be because of stronger field curvature of the 12-24, as I did focus bracketing, and none of the shots of the 12-24 was as crisp in the corners as was the 18-55 II.

I also have the feeling that the distance shots I uploaded are sub-par. If I see the review results on dpreview of the Tokina 12-24 or of the Pentax 12-24 on photozone.de, it is clear that this lens should be a superior performer even in the edges. The results I got are more what I would have expected from a Sigma 10-20, which is known to be weaker in the corners.

I might repeat some of these shots, doing long-distance shots with the 18-55 II, as well. At least the 12-24 must not be worse!

gattofix
07-26-2009, 06:21 PM   #7
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Just a data baseline check here: Did you use a tripod on all of these? Was SR enabled?
thanks,
M
07-27-2009, 03:20 AM   #8
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Real life shots in bright daylight with tripod?!

QuoteOriginally posted by Miguel Quote
Just a data baseline check here: Did you use a tripod on all of these? Was SR enabled?
thanks,
M
No, I did not use a tripod.

However, it was still bright, and I paid attention to not getting too slow shutter speeds. I used shutter speeds where even without shake reduction I should not have blurred photos. But for the record, shake reduction was on.

Also please notice that the center is always sharp, so shutter blur is, at least for the vast majority of these photos, out of the question.

gattofix

07-27-2009, 07:18 AM   #9
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Thanks for the background information. I've only the time to download a few of your samples. While the lack of a tripod for the shots under 1/120 sec doesn't help, overall the few shots I've seen appear just fine to me.

M
07-27-2009, 12:23 PM   #10
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Gattofix i got exactly the same problem.... +10 correction and v'got still bf... strange thing is that it wasn't like this before.... one day i just put the lens on a camera and suddenly problem showed up... i had the same problem with 50-135 but i just switched correction from +3 to -4 thats it... ones i buy another body i will send the camera and lens for adjustment....
07-27-2009, 01:15 PM   #11
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Thanks for looking.

I have done some more test shots. These have convinced me of the same - the sharpness of this lens is at best excellent. If you are interested, here are four shots, two at 12mm, two at 18mm. These were taken pretty late in the evening, but you can see the detail well:

http://sd2.1und1.de/qxclient/?username=@nonymous&path=2009-07-27-DA12-24-K10...84EF45932F7018


If not, there seems to be a sub-optimal focussing involved.

This leads me to the remaining problem - the AF problem. If I use the lens without the AF correction in the debug menu at +110, the lens keeps focussing past infinity. This happens like this:

I aim the camera at the building on the other side of the road, which is about 15-20m away. The camera sets the AF already "past" infinity (not right in the middle of the infinity symbol, but right at the limit). If I then point at the buildings which are far more distant (hundreds of metres away) the camera wants to focus further but it cannot, and this invariably results in an AF error (blinking in Viewfinder).

As my K10D AF was adjusted just 3 months ago and works pretty well with all the other AF lenses I own, it has to be the lens which is at fault here.

I might try to get in touch with the Pentax (outsourced) service here in Germany and ask them if they think they will be able to adjust this. If so, I might keep the lens and have it repaired after the summer - at least I now know that optically it is fine.

Thanks again for looking
gattofix
07-27-2009, 02:07 PM   #12
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QuoteOriginally posted by filorp Quote
Gattofix i got exactly the same problem.... +10 correction and v'got still bf... strange thing is that it wasn't like this before.... one day i just put the lens on a camera and suddenly problem showed up... i had the same problem with 50-135 but i just switched correction from +3 to -4 thats it... ones i buy another body i will send the camera and lens for adjustment....
Good that you have the K20 at least, my problem is that if I set the K10 in the debug menu to the necessary +110, all my other lenses are off!

If you set your lens to +10 do you only have slight bf, or still a severe one? Do you also get this focus error signal, when the lens because of the bf tries to focus past infinity? This is the most annoying for me. It clearly reminds me that things are not as they should be.

I am actually wondering why Pentax does have NO quality control whatsoever on a lens which now costs around 1100,- here in Germany! How can they send me two defective lenses in a row?!

My other lenses need all +40 to be spot on, so I am wondering... If I sent in the K10D and the 12-24 for adjustment, then afterwards my other lenses might be completely off... Or do you know if they can actually make an adjustment in just the lens?

Not sure what to do, I can still return the lens, but this is my second copy already, the first copy was even worse...

gattofix
07-28-2009, 04:55 AM   #13
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QuoteOriginally posted by gattofix Quote
If you set your lens to +10 do you only have slight bf, or still a severe one? Do you also get this focus error signal, when the lens because of the bf tries to focus past infinity?gattofix
i got subject in focus, not at the center but with slightly pronounce BF (on a focut chart sheet of course) for a long distance the problem desapear for obvious reason: BIIIG DOF). Hawever without correction the lens hits limit of infinity and green bulb starts to blink - yes. I had similar problem with 17-70 after first repair it happened at 17mm: hit - green blink..., i have sended back for repair at the same day i got it from first repair, its going to be third month without DA17-70... since i'v sendet it first time
07-28-2009, 08:02 AM   #14
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no problems with my copy. It focuses very quick and very accurately
07-28-2009, 09:10 AM   #15
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QuoteOriginally posted by jackbullet Quote
no problems with my copy. It focuses very quick and very accurately
you would be suprised what pixelpeeper can find on a perfect picture....
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