Originally posted by tibbitts The 17-50 doesn't test much better than the 18-135???
GO to photo zone and have a look. They both test better than any Pentax Prime available in the 20- 40 range, except for the 31 ltd.
DA 18-135
Look at the 18-135 at 24 mm, At 24 mm It has excellent Center and edge sharpness with edge sharpness up near the limits of the test. I've included the 31 ltd, just for comparison. This constant ragging on the supposed weakness of the 18-135 is completely unjustified, in that at about 20-28mm, it's probably better than any Pentax prime available in that focal length, for sharpness. The Tamron 17-50 tends to be better, across it's range, and it's 2.8 constant, so double bonus, fast and sharp.
I haven't tested any of the Pentax primes in that focal length, except the 21 ltd, and won't say the 21 is sharper, but, my guess is it has much smoother bokeh, the rendition just seems to be more pleasing.
Klaus clearly had a poor copy when he tested it's lens, and it's still stellar for a super zoom. You can read a hundred posts trashing this lens, but not one of them uses the tests to justify their position. They all rely on Klaus confusions ( ha ha, I meant conclusions, spell checked again) , which severely punish the lens for poor edge performance at 135mm, on his copy.
Just from the sample posted, my conclusion would be the 31 ltd, arguably the best lens available for the mount is special because of it's handling of OOF areas, and really that, not sharpness is the area where a prime is likely to have an advantage on a zoom. If you have no out of focus areas, either the 18-135 or the Tamron 17-50 is going to give you a sharper image.
Here's a 21 ltd image, smooth and dreamy...
Here's a 18-135 at 28mm
There is a difference in rendition, but it's not about sharpness.
Last edited by normhead; 01-18-2014 at 07:50 AM.