focusing issue

[HuntingMartians]

The problem I have is...

Today I went out with my camera and I had my tamron 70-300 mm lens attached to my pentax k20D. Now I have never ever had an issue with focussing with this camera or any lens. But today it just stopped working in auto focus. The auto focus ring would just turn all the way and then return the other way trying to focus on an object. Then some times it would actually focus on something. It was random hit and miss. I am unsure if I may have lent the auto focus ring on a fence when trying to steady a picture. Would this have damaged the lens when it had a little resistance to the auto focus ring when focussing?

When I got home I changed lens to a sigma 10-20 mm and tried to focus in low light conditions and the camera and lens seemed to work and focus. I have still to try with a sigma 30 mm prime and then a pentax 18 to 75mm to check the camera.

Since I have never had this issue I am just looking for advice. Is it a camera body issue or a lens issue??

Any help would be great.

 

[arclight]

I had a K20d and the only times the focus system "hunted" as you describe was when I tried to focus on a dark object against a dark background or a flying bird. That is not a fault, but just system limitations.

If you were trying to focus on a low contrasting subject that could explain it.
I think you need to conduct further tests with other lenses and again with your 70-300 to see if the problem persists.