OK, I`ll apologise straight away, in that what I am going to ask has been covered in other threads at earlier times - but I`m trying to avoid trawling through.
I have a K20D with Tamron SP 17-50 f2.8 plus a recently purchased Pentax SMC 28-105 f3.2-4.5 (which was a good buy I think). I would like a telezoom that extends up to 300mm to complement these.
If money were no object I`d get the Sigma 100-300, but it`s out of my reach financially. So the choice is either the Pentax 55-300, Sigma APO 70-300, or possibly the Tamron 70-300. My prime requirement is for sharpness/image quality; I have no need for Macro and won`t hardly ever want to use `wide open` - more like f8-11. Nor am I bothered about weight or how far the barrel extends at the long end; most of the time it will be tripod-mounted. Built quality/durability is an issue though.
In reviews I`ve read, the Tamron seems to be the poorest performer, but every time I read that the Pentax is the best, along comes another one that says the Sigma will give the better image quality. So - help please!

Decided to go for the Pentax 28-105 f3.2-4.5. Have bought it (from Microglobe) but still waiting for some half-decent weather to try it out!!

I think £250 is a lot to ask, even though it`s mint. I`ll see if he`ll take £200.
Any views on the Pentax 28-105 f3.2-4.5?
Thanks for yor thought on the 55-300 John. Will trawl the internet for the best price.

I have found in a nearby photo dealer a mint 24-90, mine for £250. Is this a good buy? Or should I go for the Pentax 28-105 which I notice Microglobe have available for £167. Which is the better optically?
Also I could do with an autofocus zoom that goes up to 300mm. Don`t want a superzoom (not good enough image-wise) but can`t afford several hundred pounds. Is the Pentax 55-300 the best buy?

I`m mainly into landscapes, architechture, steam trains, shipping, some portraiture. No real need for macro. Really need a lens that`s a bit faster than f5.6. Lens quality is everything. Happy to spend up to, I guess, £350.

Recently bought the K20D, and am well pleased with the results. I use the Tamron 17-50 f2.8, plus an old - but excellent - m/f Tokina 80-200 f2.8.
At the risk of repeating what may have appeared on here before, I really would like a good quality `mid range` zoom; something like 24-80 or even better a 28-105. Pentax don`t seem to make a modern one; but what about their older autofocus lenses? Which is the best please?