Infinity Focus - Pentax 50-135

My 50-135 will not lock onto focus at infinity anymore. This happens right across the zoom range with both manual and auto focus. I've tried it on two bodies with the same result, so I assume it's something to do with the lens. The motor seems to take it to the focus point, at infinity, but it does not lock so the shutter will not operate. Funny thing is at shorter distances, say up to 30ft, it works fine. Any comments, suggestions, am I missing something?

Have had a similar problem with my da 16-50. This tends to occur more in low lit conditions. Strange thing is that it comes and goes. Only thing i do is change to manual focus and set things into there. In the end, at infinity manually setting your focus is quite straight forward. Sorry, more than that cant help. Bloody SDM!!!!!!!!!!!! Drives me mad!!!!!!!!!!

Hi I do have exactly the same problem with the 40mm DA on the K5. Both are new.
If focusing at infinity, the AF will not confirm and not release.
Sometimes after waiting for a while the shutter finally fires.

I also have the 70mm and the 21mm. In exact the same situation the 70mm will work fine. The 21mm sometimes also "hesitates" a bit but then releases.

Now I don't know if its the camera or the lens problem.

Did you guys find out something?

Besides that the 40mm and 21mm ar both super sharp and contrasty. specially the 40mm. and the bokeh from 40mm is great. the 70mm is overhyped on the reviews compared to the 40mm, which doesn't always get the best reviews.

I m coming from nikon d700 with 85mm 1.4g and 35mm 1.4g, so I know what Im talking about Nikon has great quality and in low light the images are superior as well as the AF is more intelligent. I like the color from Pentax though and the sharpness - which can result in nice clear pics.

Reply from Asahi Photo Ltd in response to an email giving details of fault.
"We can repair your 50-135 DA Lens, it seems that the focus mech is out of calibration. The cost to repair and service the lens would be £72 which includes parts, labour vat and postage back."

ok so it seems like a lens problem. I will return my lens then, hope the next copy will be just as sharp