[micromacro]

I bought it second hand DA 70mm f 2.4 limited, used about 3-4 times, then noticed that first AF started hunting, and the lens focuses only on closer objects. AF of MF simply don't focus on subjects far than about 20-30 feet. The focus confirmation does not work, lens even don't try to refocus on distant subjects, and pictures come out blurry.
There is no problem with focusing on closer distance subjects at all.

I don't think it's some adjustment issue because the lens worked before, then just stopped focusing on distant subjects. It's not the camera issue either, any other DA lens works like a charm.
Any ideas please? What it can be?

[Na Horuk]

What about manually, can the lens achieve far focus at all?
Make sure lens is clean on the back side (back element, contacts, AF contact), as well as the camera's mount. the lens isn't mounted on some type of extension tubes or adapter or TC, right?
Oh, and make sure you have the latest camera firmware, especially if this is an HD DA 70mm ltd

[micromacro]

Na Horuk, I can't focus manually either. The lens is clean like new, camera mount does not have problems either, no adapters or tubes of course. How filmware can be a problem, if the lens worked fine just a week ago? I use it on K5iis.

[biz-engineer]

That could be mechanical play due to damaged quick-shift mechanism. AF works only at short distances but does not work as it's getting closer to infinity. It is still possible to focus manually when fully turning the AF ring and than a continuous rotation in the same direction to avoid hysteresis of the mechanical play. That the problem I have on the DA40, the way to repair it is to replace the small quick shift gear.

[micromacro]

That could be mechanical play due to damaged quick-shift mechanism. AF works only at short distances but does not work as it's getting closer to infinity. It is still possible to focus manually when fully turning the AF ring and than a continuous rotation in the same direction to avoid hysteresis of the mechanical play. That the problem I have on the DA40, the way to repair it is to replace the small quick shift gear.

Seems like you are right, it feels like mechanical problem inside the lens. Compare to yours, and mine old broken F 35-70mm lens, when it's possible to "help" focusing with fingers, in case with DA70 it's not possible at all. It does not move to focus on long distance at all. Like it's stuck pretty well.
So, what to do now? Who can fix it? If it makes sense at all depending on price.

[Paul the Sunman]

Are you saying it won't manually focus near infinity? Does the focus ring turn all the way to infinity, but it's still out of focus, or it won't physically turn that far? If you don't have the full range of manual focus, maybe there's some grit in the mechanism stopping it. Do you have another body you can try it on?

I find focus on the DA70 to be very fast and accurate. A dusty front element can interfere with AF, but that doesn't seem to be your problem.

[micromacro]

Are you saying it won't manually focus near infinity? Does the focus ring turn all the way to infinity, but it's still out of focus, or it won't physically turn that far? If you don't have the full range of manual focus, maybe there's some grit in the mechanism stopping it. Do you have another body you can try it on?

I find focus on the DA70 to be very fast and accurate. A dusty front element can interfere with AF, but that doesn't seem to be your problem.

Yes, focus ring turns to infinity, or seems to be on infinity, but it is still out of focus on anything far than 20-30 feet I try to focus. If I switch to closer subject, AF works like a charm. If move away to 20 feet or so to focus, it's just a "stuck" sound in AF without any movement, and no movement in MF at all. None.

I do have K200D, it's a good idea to try although I doubt it will help since DA 50mmf1.8 and other F, FA lenses I have, don't have any problems at all. It must be the lens itself.

And yes, DA70 WAS fast and accurate before it started "hunting" and stopped focusing on infinity. The short period of hunting then stuck...


P.S. Checked on K200D. The same.

---------- Post added 04-18-15 at 10:09 AM ----------

Ok, now it's a big question: what to do?!! Where to fix, or not to fix?

---

Last edited by micromacro; 04-18-2015 at 09:53 AM.

[Na Horuk]

Yeah, sounds like a mechanical fault with the gears. Make sure the lens' barrel and focusing ring are clean, there are no particles in there.
I don't know if the DA 70mm is easy to diassemble, probably its not, so you might have to send it in for returns.

Was the lens dropped or anything like that?

[Paul the Sunman]

There a detailed set of instructions for disassembling the DA15 in a recent thread https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/292630-repa...aged-da15.html. It may give useful hints for the similar DA70.

[micromacro]

Lens or camera have not dropped, not hit by anything, nothing like that. I will not even try to repair it myself. Return is not the option, since I bought it third hand from the forum member, and it worked just fine when I received it. I guess I just lost my money.