I contacted Sigma UK about the non-availability of long lenses, 150-600mm in particular, in PK mount, their response was :-

We don't provide all of our lenses in Pentax mount - Only a few. This is due to the global demand for Pentax fit.
If we see an increase in demand we will produce more Pentax mounting lenses.

Surely this is self defeating, if a product is unavailable no one asks for it. If you would like to see this product and similar become available, please contact Sigma UK and let them know there is an untapped market out there.

Seamus

My apologies for a late reply. I have resolved the focus issues. When looking at the images I intended submiting, I notice camera shake on the fine catchlights. I have reset the tension on my tripod head. This has resolved the unsharp image problem.

Thanks for your support in this matter.

Seamus

thanks for the quick replies. 1. Where do I post examples. I use a sigma 28-300 1:3.5-6.3 and a sigma Ex 50-500 1:4-6.3.

I cannot get a sharp image on my K20D, i have tried high shutter speeds, autofocus, manual focus, shake reduction and a repeated all of this whilst the camera was on a heavy tripod. I even read the instruction manual.
Has anyone eles had similar problem and how did you resolve it.