[Jool]

I bought a K-5 a few months ago, my first digital camera. Using it around home everything seemed to work fine but I didn’t use it extensively until I went on vacation this past week. The very first day we were overlooking a lake and bluffs. The autofocus wasn’t working properly. There would be a slight motor noise, the focus confirmation light would blink as trying to focus but would not lock in. I thought to myself that I should have brought my film camera as a backup. I never had this problem with my film camera and this lens (Tokina 28-70 2.8). I thought maybe there was not enough contrast in the trees, but it happened when focusing on people and other things. There was adequate light being late morning when this first occurred. Throughout my trip this happened off and on, much more when the zoom was at the short end. When I zoomed in a little it seemed to help some. The only settings I changed from before my vacation were ISO, aperture, and speed. I was able to get it to work good enough to take a ton of pictures, but for a camera at this price point it should be more dependable. I will be contacting Pentax on Monday to see what they have to say, but if anyone has any idea of what the problem was I’d like to see what you think.

[Adam]

Try adjusting the AF a bit- it sounds like the motor is trying to move the lens past infinity.

[Jool]

Are you talking about the AF Fine Adjustment or some other AF adjustment? If it is the AF Fine Adjustment what setting do you suggest trying (step 4 on page 126 of manual)?

[Adam]

Yes, the fine adjustment. I don't recall which way is the right way, but try +5, and if it doesn't fix the problem, try -5. After applying this on some of my wider FA lenses (such as the 20-35mm), it focused at infinity w/ no problem.

[octavmandru]

Adam, can such issues be caused by the imperfect contacts between the lens and the camera? I never had issues any with AF locking, even in pitch dark and low contrast targets. Actually, this is the biggest improvement compared to K20, second to the IQ.

OP, did you upgrade to latest firmware? And, can you try another lens?
I remember I had similar issues with the 18-55 on the K20, and cleaning the contacts used to help.


Octav

[Rupert]

I have a Tokina 28-70 2.8......nice lens, I love it.....I have no problem on my K5 with it, but once had the exact problem you have with it on my K20D. I had a sticking contact, found by a friend and worked with a toothpick until it was free moving. No problem since. I have also had this since then on another lens, once, so I would check the contacts to make sure they are free moving.
Regards!

[Adam]

I've experienced the problem myself with wide lenses on multiple bodies, so I think it's just a slight AF misadjustment. I'm very happy for the fine adjustment feature, as my wide lenses can finally lock without problems. All the lenses were screwdrive, not sdm- so maybe it's an implementation problem? In any case, not a big deal any more.

[octavmandru]

Thanks Adam, this is good information.

Octav

[Smeggypants]

Make sure you have at least FW1.03 install before making any AF adjustments

[Jool]

I upgraded the firmware as soon as I got my camera. I tried the fine adjustment both ways as Adam suggested but at the short end it still has trouble locking focus. I tried my Tokina 80-400 and there doesn't seem to be any problems locking focus on that one. I will try cleaning the contacts but since it only seems to have problems at the short zoom end I don't really think it's the contacts.

[Jool]

I called Tokina today and they said that the lens elements would have to be adjusted to work better with a digital camera. So, nothing wrong with the K-5 or the AF adjustment feature, the lens was designed for film cameras and not digital. Even though the mount is compatible, the way the lens works isn't. At $100 to fix it I think I will forgo repairing it and use it with my film camera. They said they may not even be able to adjust it. With the crop sensor I need something wider anyway. I did post in the lens section suggestions for a new zoom lens. The 16-50 2.8 seemed to be the hottest topic with some liking it and others disliking it, so mixed feelings about that lens. At least I know now what the problem is. It's strange I didn't notice it over the last few months at all until I went on vacation, but it happens much more on objects father away and only at the short end of the zoom. If anyone has suggestions on lenses see my post in that section and reply. Thanks for your help with this issue.