I've had my DA 50-135 for 3 days now, and its everything folks said it was: great IQ, rendering, bokeh and nothing unusual in the focusing department (except that its extremely quiet)
I didn't have access to my computer equipment for the first day, so had to check image sharpness with the LCD. I noticed right away that i had to significantly increase my normal magnification to find a lack of sharpness. This seemed true till i reached the telescopic FL of 135mm.
Negatives from a few reviews:
a. There was one website review that observed on their copy that there was softness at 135 FL F2.8. I have a Pentax A 135 f2.8 which i think highly of so i took one handheld shot with the DA at 135mm and then 2 shots with the A135 f2.8 of a line on my deck 10 feet away. With 1:1 crops in Lightroom, i saw no difference in sharpness between the two lenses. With 2:1 crops in Lightroom, I could now observe that the A135 f2.8 images were sharper than the DA 50-135. (One review in Pentax Forums Database indicated that at F4 and above, the reviewer thought that the two lens were equal) In any case, i'm happy with 135mm focal length image quality.
b. One reviewer indicated that the hood was pretty flimsy in its attachment. I didn't notice that to be a problem. The hood attaches like a bayonet in the same way as the DA 300. It inserts axially, than rotates clockwise until it hits a partial stop, and then snaps into place. The action is lighter than in the DA 300 but adequate IMO.
c. One reviewer thought that the range should be higher than 135mm. Of course this is a personal thing. I spent one day walking along the shoreside of Port Townsend, taking architectural shots, and seashore scenes. In the long exposure nightime scenes that i enjoy doing, as well as the local playhouse stills that i take for them, this FL range is ideal for me. If anything, i would like to see a slightly wider FL.
d. The one complaint i have is that when i mount this on my tripod ball head, and then flip that ballhead over to a vertical orientation, i find that there is a tendency for the weight of the lens to loosen the camera body on the mounting stud. So this requires a firm tightening of the mounting stud collar and care in handling the camera body in the vertical orientation. Considering the many other virtues of this lens, its a small price to pay :-)
Here's two images of the DA 50-135 compared to the Tamron 18-250. The problem i had with using the Tamron for theater work, is that i often found myself at F5.6 and ISO speeds of 1600 and greater. With some F2.8 primes that i tried, one could work at ISO 800. Please note that on the first image, that i'm trying a 1 inch deep rubber BW hood from B&H instead of the provided plastic hood. Also note that the DA extends 5 1/4 inches from the mount to the end of the lens, not including hood. The Tamron, fully extended is about 6 7/16" long to the end of the lens. The Tamron weighs one lb while the DA is 1 1/2 lb. The only reason i'm doing this comparison is that many Pentax folks have tried the Tamron or seen it and might be able to relate to the DA's physical size that way.
In the next image, the supplied DA hood is installed. Its 3 inches deep compared to the 1" depth of the rubber hood that i bought from another source:
The next image shows that the DA 50-135, installed on a K10 or K20 fits nicely into the Lowepro 200 AW slingbag with about 1/2 inch to spare. The rubber hood may be collapsed and left on the lens for storage while the plastic hood would have to be removed and stored in one of the pockets:
Finally, IMO, the following 3 lenses would make a nice light-weight walk around kit. Of course, many other light weight short FL lenses can be substituted for those shown.
Whether one likes to shoot with primes or zooms, i think we can all admire an excellently designed lens. The large shape of the DA 50-135 enables the lens to eliminate the normal telescoping 3 sleeves such as the Tamron design, which would be a nightmare to seal for water resistance. The strong shell is likely to be more resistant to physical abuse than a telescoping design.
This lens is a class act all the way. The second day i had it, I used it to take portrait shots of 21 actors for a Shakespeare play brochure. The shots looked professional and got compliments.