Hi Roger
You havent seen all the worrying I did before I realised that good lighting a good subject and high contrast help this lens perform. First impressions are that your lens is not performing as it should but it may not be a focus issue--
Do a test on a fence that is running away from you at a slight angle. Set the camera to f8 or smaller aperture if possible, focus on a part of the fence some distance away (Mark it with chalk so you will see the bit you focused on later) Take several shots at different speeds etc.
Then review the shots in camera and on PC. The sharpest area should be the part you focused on.
Remember
1) The camera MUST NOT be set to Manual Focus
2) The Sigma lens OS must be set on if hand held, especially at full length
3) The camera OS must not be set
4) Ensure you avoid over exposing images, slight under exposure can be rectified and gives you the chance to up the shutter speed
5) If possible take only RAW photos
6) The Sigma seems best around f8 and shutters above 1/200sec if possible
7) My K7 doesnt seem good especially in poor light above 1250 ISO

Hope this helps best wishes
David

Wow and WOW, I dont know me, the K7 or my lens but I have never had results like this from my Sigma yet and I have had it for months.
Best Regards David

Just brilliant in every way possible
Regards David

I'm still trying to achieved a result to match the above photo using a Sigma 150-500. Therefore you have to be careful not to dismiss cheap as always nasty. Can you take the risk that is the question?
Regards David

I had very limited money to spend on a long lens so had to be realistic as to what I could afford. So after much deliberation I recently bought a Sigma 150-500 AF/OS. I tried one on an non Pentax camera in poor light and was not too disappointed with the results, so when the price dropped from £850 to £600 I took the plunge.

On the Plus side-----
Excellent value for money
AF can be very fast and quiet
Given right conditions results can be stunning
Perfect for my needs and wildlife shots

On the Minus side----
In poor light results dissapointing
Rather heavy
Not Weather/dust proof (No problems yet but kept it dry so far)
AF can be slow or non existent with poor light or certain subjects.
Regards David

Hi Kevin
In the statement from your blogger friend I find that there are two words that stand out and they are the words "should" & "cost"

Maybe the pessimist in me will be proved wrong one day soon lets hope so.
Regards David

Dave
Do you know I'm sure I saw a pig flying over the house this morning so you never know you may be in luck, if not we may have to wait about 20 years and look on ebay!!!!!
Regards David

Interesting there may still be hope for us Pentax Users, it's about the future release of f5.6 560mm lens and other new products.
Amateur Photographer link below http://www.amateurphotographer.co.uk/news/Pentax_makes_development_announcements...

Regards David

I used to shoot RAW + JPEG but once I got used to Adobe RAW editor I stopped bothering with JPEG altogether. I only ended up junking all of them anyway.
RAW means you can regain and enhance so much detail that may not even exist in JPEG's.
Regards David

Stop it, your making me jealous. Brilliant capturing of wonderful scenery.

Regards David