Unable to get focus lock at infinity?

I have a DS and recently purchased a DA 12-24mm. One thing I noticed right away with this lens is that the camera will often struggle to lock focus on distant objects even in bright daylight.

For example, aiming at the top of a tree, the camera will attempt to focus, the focus motor operates briefly one time, and the camera gives up and displays the blinking out-of-focus indication. If I move the camera and aim on another nearby point, I'll usually get a focus lock & beep but without the focus motor operating because the lens is already at infinity. But then I can aim again and it will fail to focus, motor noise and all. The camera will also often fail to focus to infinity from a nearby focus point.

I started noticing this while playing around with the 12-24mm especially at 12mm. But it does it at other focal lengths too and it also does it with the kit lens. It doesn't do this every time, but often enough to make me wonder if I need to send the camera in for repair. I honestly do not remember if it did this before I got the new lens. Once the camera focuses the pictures are fine, by the way.

Has anybody else experienced this?

The only thing I can think of that I might have done is a sensor cleaning that took a lot of tries to get done. Could I have nudged something out of place?

Have you set the camera to focus on the centre spot only? If not, then doing so will probably help considerably.

Occasionally all AF systems will be defeated, but I have not experienced the sort of problems you mention and I have been using the same lenses.

What are you focussing on? My understanding is that the camera looks for defined edges, so if your target is say, a solid area, it may not be able to focus on it. http://www.howstuffworks.com/autofocus3.htm

Hi, as an example I try focusing on a treetop or a building far enough away for the lens to be at infinity. No solid areas.

Used to have the same problem with my old DS, sometimes it would and sometimes it wouldn't.

Couldn't see any reason why, another way round it was to point the camera at my feet, auto focus and then point back at what I wanted to take a picture of and it would work.

In the end I just used to put it in manual focus for landscapes etc...

Now I've got a K10D the same lens works perfectly with no focus lock issues at all.

Can you focus manually at infinity with this lens?. What about other lenses, do they focus manually at infinity?

If this is your only lens which can't be focussed manually at infinity, then the lens is faulty. I've managed to tweak 2 of my older lenses which didn't focus at infinity. They do now, but I'm not certain I would try it on a new and expensive lens like this. If it proves to be faulty, send it back.

Yes, I can focus manually, and I have the same behavior with the kit 18-55mm lens. It's odd behavior. I've written Pentax and I hope they can shed some light on this.

Thanks for all the replies!