I just received my new DA* 50-135mm F2.8 lens in the mail a few days ago. I tweeted about wanting a subject to test it out on. John Shafer answered my tweet and we met up the next day near the University Hospital at the U of U at the foothills of the mountains. John wanted a portrait of himself with his biking and photo gear.
I used a single Sigma 530 Ef DG Super on a stand with no umbrella and a poverty wizard, to camera left to fill in shadows in the evening sun.
I found the 50-135 to be smooth. It is much lighter than the Sigma 70-200 which I have used and like. I waffled for months on which lens to get. I decided the Pentax glass would do what I wanted best. Shooting people, glamour, boudoir, events. Some day I will add the Pentax 300mm to my glass library to take care of the longer end of things.
The 50-135 is lighter than the 70-200 and makes it much more comfortable to use. So far I find the auto focus with my K10d to be quick and accurate. I like the bokeh, and find images to be very sharp. I will write a review in about a week.
It was nice meeting John.