telezoom choice

maybe not for this topic, but, focal range quite similar..
I always look at pictures, shooted with Canon 70-200 f2.8 (and f4 as well), with great admiration, the sharpness is excellent and almost recognizable among the other pictures.
Question is- which Pentax lens is similar to the sharpness and image? not necessarily telezoom..

Well first of all, Canon seems to sharpen their photos a bit by software, Pentax default settings with JPG is quite soft so for get that detail for now.

Pentax is now making althose classic focal lengths for APS-C sensor (1.5x crop)
The DA*50-135 f/2.8 is the digital equivalent what the 70-200mm f/2.8 was on 135mm film.
If you want that range though the only thing pentax has is the DA*60-250 f/4

The DA* (with the star) are the high grade/professional lenses, maybe not so pro as the super high end of Nikon or Canon but the price is important here, you can buy a car with some of the Canon/Nikon lenses.

I'm not interested in similar focal lenght, that's no problem..
I'm interested in image quality..
"..DA* (with the star).." could be a real answer, maybe..

If you want pure image quality then I think it always comes down to primes, certainly in terms of value for money. You'd have to spend a fortune on a zoom to get one able to beat the old K 55mm f1.8 or the various 50mm f1.7 variants.

Yep the DA*, FA* or any other with a *star are the better lenses.

The limited series and certainly the FA ones are also very very good, and like Matt said any prime will also be better then most zooms.

Sorry for the novel, but here goes :

Stefan, in my admittedly (very) limited experience, I have found the Sigma to be sharp across the board. Also, in my limited, and unscientific testing the Sigma gave me the best overall results of the 3 lenses I looked at. Price wise, it was in the middle of the price range of the 3.

Our local camera shop has a 21 day return policy - buy a lens and use it for up to 21 days. If you don't like it they will take it back and give you a full refund - assuming it is in original condition, with all the packaging etc. If that is an option it may be the best way to be sure you are getting what you want/expect.

There are a lot of folks here with a lot more knowledge and experience than I have (or will probably ever have) so listen to what they have to say. These are only my observations, and potentially flawed opinions.

Personally, I have a strong aversion to chromatic aberration. The Tamron was the least expensive, but had the most CA (a lot in my opinion). The Pentax displayed less CA than the Tamron (probably livable, though still troubling to me). It was more than double the cost of the Tamron, and ~30% more than the Sigma. The Sigma had the least amount of CA - hard to see even after cropping, and was at least equally sharp to my eyes. And regardless of the price, I am more than happy with the results it has given me.

Here are some samples - all are shot at max zoom (300mm). I'm not sure what percentage the crops would be considered, but they are all cropped deep into the originals.

Pentax smc DA 55-300 @ 300mm
link

Pentax smc DA 55-300 @ 300mm - Crop - some CA visible
link

Tamron AF 70-300MM @ 300mm
link

Tamron AF 70-300MM @ 300mm - Crop - lots of CA Visible
http://picasaweb.google.com/RobStr86/TestShots#5431573227082738738

Sigma 70-300 @ 300mm
http://picasaweb.google.com/RobStr86/TestShots#5431571515928976546

Sigma 70-300 @300mm - Crop - very slight CA visible - see extreme left side of full version
http://picasaweb.google.com/RobStr86/TestShots#5431574086382583394

Sigma 70-300 @300mm - Crop - very slight CA visible - see middle left side of full version
http://picasaweb.google.com/RobStr86/TestShots#5431569446211841474

Unfortunately I was not able to test the Sigma in the same location, and under the same conditions as the Pentax and the Tamron. But I think the Sigma shots are still high contrast, on a bright day, which should exaggerate/cause CA to appear if the lens is going to produce it.

Ultimately I am very happy with my decision, and for me that's the bottom line. Do your research, test if you can, and choose the lens works best for you.

JD