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03-04-2010, 05:58 PM   #1
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DA 17-70mm having trouble focusing above 50mm

I currently have a DA 17-70 which is having some trouble focusing above 50mm. Below 50mm there's no issue. It focuses very quickly and almost never hunts, even in very low light. Above 50mm, especially when it maxed out at 70mm, there are times when it simply won't lock properly. It gets very close and then twitches right around the correct focus point. This occurs even on well lit, high contrast targets.

The strange part is that if I am touching the focus ring (even very lightly) while using the AF, it seems to add just a little resistance to the focus ring, and it locks at 70mm without issue.

Now I am assuming that unlike my 50-135, the focus ring on the 17-70 is suppose to move when I am using AF. I am also assuming that it is normal that the focus ring on the 17-70 seems to have almost no resistance when you turn it manually.

Anyway, just wondering if anyone had any ideas about what might be going on. It's not a huge issue as the lens pretty much works perfectly most of the time and I can "make it" work 100% of the time by keeping a finger against the focus ring when I use longer focal lengths. I guess I am basically trying to figure out if it would be worth sending it in for an estimate (it's out of warranty) or if I should just continue using it like this.

03-04-2010, 07:24 PM   #2
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ITS UNBELIEVABLE!!! I had exactly the same issue.... mein landed at the service - thay changed pcb and something what is responsible for af confirmation during communication betw camera and lens.... it took 4 months to fix it.... good luck (lack of good luck i would say)!
03-04-2010, 09:19 PM   #3
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QuoteOriginally posted by filorp Quote
ITS UNBELIEVABLE!!! I had exactly the same issue.... mein landed at the service - thay changed pcb and something what is responsible for af confirmation during communication betw camera and lens.... it took 4 months to fix it.... good luck (lack of good luck i would say)!
It's really weird that it only happens at or near 70mm... was that the case for you as well? Also, do you recall how much it was for the repair?
03-05-2010, 04:18 AM   #4
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QuoteOriginally posted by dgaies Quote
Above 50mm, especially when it maxed out at 70mm, there are times when it simply won't lock properly. It gets very close and then twitches right around the correct focus point. This occurs even on well lit, high contrast targets.
Send it in for repair.

QuoteOriginally posted by dgaies Quote
Now I am assuming that unlike my 50-135, the focus ring on the 17-70 is suppose to move when I am using AF. I am also assuming that it is normal that the focus ring on the 17-70 seems to have almost no resistance when you turn it manually.
Yes and yes.

QuoteOriginally posted by dgaies Quote
I can "make it" work 100% of the time by keeping a finger against the focus ring when I use longer focal lengths.
You're just making your lens worse by this way. During autofocusing you should never touch the focus ring! Unless you want to eventually brake AF in your lens...

03-05-2010, 06:02 AM   #5
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QuoteOriginally posted by dgaies Quote
It's really weird that it only happens at or near 70mm... was that the case for you as well? Also, do you recall how much it was for the repair?
as simico said it was above 50mm.... and lens was within warrenty period so i have no idea haw much thay charge
03-05-2010, 07:57 AM   #6
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QuoteOriginally posted by simico Quote
You're just making your lens worse by this way. During autofocusing you should never touch the focus ring! Unless you want to eventually brake AF in your lens...
I didn't mean to imply that I was actually holding the focus ring and preventing it from rotating, otherwise I agree that you would risk putting too much load on the focus motor. What I meant was that if I allow the focus ring to freely move through my fingers to the point where ridges of the focus ring just barely graze my fingers, the addition of that *slight* amount of resistance allows the lens to obtain a focus lock above 50mm. I'm not saying that even doing that is good idea, I was more throwing it out there as another piece of information in case that hepls someone identify the problem.
03-21-2010, 04:36 AM   #7
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dgaies
I purchsed my 17-70 a couple of weeks ago and had focus lock and low light focusing issues. Fortunately I had a 14 day return / exchange policy in place and they replaced it with a new lens and sent the original back to Pentax.
The new one is working fine (so far after a couple of days).
And yes, be careful to not touch the focusing ring when in Auto focus.
06-15-2011, 11:18 AM   #8
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I thought I would resurrect this thread. I have the same problem when using my DA 17-70 on my K20D. This is my second lens, the first I did the same thing after a few months of using it (or I just noticed it then) and I set it in for warranty repair last year. After 2 months I got a replacement lens because they said they couldn't repair it. The new lens at first seemed OK but eventually exhibits the same characteristics. My dilema is that I like the lens very much both in range and optically.

I wonder if owners of newer Pentax bodies have any similar problems when using the DA 17-70 because I'll just upgrade the body instead of getting another lens. If it's just a DA 17-70 problem then I guess I'll replace it with a DA* 16-50 even though I use the 50-70 range often.

06-15-2011, 11:34 AM   #9
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QuoteOriginally posted by 6bender Quote

My dilema is that I like the lens very much both in range and optically.
Mine too.
+ I bought mine used without any warranty so; lucky me


QuoteOriginally posted by 6bender Quote
I wonder if owners of newer Pentax bodies have any similar problems when using the DA 17-70...
Many of us... You guys should`ve read the lens review and found the weaknesses of these lenses so it didn`t come as a surprise that the SDM on maaaaaaaany DA 17-70`s have *ahem* "a tendency" of becoming faulty

Got mine almost for free with my K20D though, so I can`t really complain. MY WIFE however loves to swear at this lens every time she uses it. But she still sticks with it on and off!
06-15-2011, 12:24 PM   #10
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My 17-70mm has the same problem. See my review @ Lens Reviews section. My camera is K10D.

It seems this is a common problem with this lens. Many times it just can't lock focus even in outdoor & on high contrast objects. Very frustrating.

QuoteOriginally posted by 6bender Quote
I thought I would resurrect this thread. I have the same problem when using my DA 17-70 on my K20D. This is my second lens, the first I did the same thing after a few months of using it (or I just noticed it then) and I set it in for warranty repair last year. After 2 months I got a replacement lens because they said they couldn't repair it. The new lens at first seemed OK but eventually exhibits the same characteristics. My dilema is that I like the lens very much both in range and optically.

I wonder if owners of newer Pentax bodies have any similar problems when using the DA 17-70 because I'll just upgrade the body instead of getting another lens. If it's just a DA 17-70 problem then I guess I'll replace it with a DA* 16-50 even though I use the 50-70 range often.
06-15-2011, 12:29 PM   #11
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When I bought a DA17-70 about 3-1/2 years ago, I noticed that it was soft at infinity near 70mm focal length. This was not due to an inability to lock focus, but due to an inability to attain sharp focus in either AF or MF mode. I sent the lens and my camera to Pentax repair service twice, along with images demonstrating the problems. Both times, the lens was returned with messages saying that it was operating within specifications. This was not up to my own specifications, so I sold the lens and replaced it with a DA*16-50, which is a much better lens, IMO. I would suggest that you consider doing the same. It seems to me that SDM failures with the 16-50 are reported much less frequently than in the past, but just to be on the safe side, you might get a Mack extended warranty, simply for the peace of mind that it will provide.

Rob

Last edited by robgo2; 06-15-2011 at 12:52 PM.
06-15-2011, 12:58 PM   #12
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Thanks for the replies. I am still interested if K-7/5, Kr or Kx owners have the same problem. I guess I'll trade out the lens then. I'm content with my K20D for now (still on warranty for another year) so I think I'll sell the 17-70 and take a chance on a 16-50 (with xtra warranty, of course). It's that "taking a chance" thing that bugs me.

Last edited by 6bender; 06-15-2011 at 01:03 PM.
06-15-2011, 01:49 PM   #13
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prije 30 dana kupio sam 17-70/4 (br. 6409626 -rabljeni- star 1,5 godina) i na k-r radi savršeno i u kombinaciji sa af pomočnim svijetlom u slabijim svijetlosnim uvijetima bez problema ulovi fokus po cijeloj dužini
07-16-2011, 04:47 PM   #14
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I sometimes have the same problem with my 17-70. It has been sent back and they replaced the AF block. Still it sometimes won't lock focus at long focal lengths. Having read the reviews for the lens, I thought this behaviour was "normal", and kind of worked around the problem by touching the focus ring if it won't lock focus. But now you are telling me this can ruin the AF?

edit: Most of the time, manually setting focus to infinity or closest distance before activating AF will also resolve the problem for me.

Last edited by starbase218; 07-16-2011 at 05:02 PM.
07-31-2011, 02:35 PM   #15
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Was: "I use this lens with My k5. Same problem. Generally, I think the lens is a disaster, with the exception of 17- 24 mm. not only focus is bad. It has a terrible quality (going soft/blured) with high contrast conditions. One of the worst lenses I've ever owned."

I spent the day troubleshooting the lens based on all comments in this thread. I would like to moderate my rather categoric statement above. My conclusions are the following (all tests conducted at f/5.6 ISO 400 using both K5 and K20d):

- Results are the same on both bodies
- The autofocus sharpness at the 17-50 range is stunning. It is better than Sigma 18-50 2.5. It is not quite up to the Pentax DA 50-135/2.8 (at 50) lens but closer to that than to the Sigma lens. The sharpens at the 17-24 range is significantly better than my Pentax DA 12-24/4
- At 70mm, the focus is very unreliable (as escrowed by other posts). With manual focus, the sharpness is very good.
- Highlighted areas loose more detail and become a bit "blur" (edges "shine" into the surrounding areas and thus look unsharp) compared to the Sigma lens. With Aperture, I could compensate for that by reducing exposure (till details are back and blur is gone) combined with adjusting the luminance channel.
- The lens is not suitable for filming since there is not enough resistance in the focusing ring. I've been folding a lot with the lens and I constantly find my self mistakingly touching the focusing ring.

Test pictures at 70mm f5.6
----------------------------------
Plain_autofocus:


Autofocus with slight pressure on focus ring:


Manual focus

Last edited by johaneltes; 08-07-2011 at 09:31 AM.
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