Out of all the alternatives that I have tried. At this moment, I can' find a close replacement for the DA* 50-135mm zoom. There isn't any lens like it except the Sigma 50-150mm f/2.8. Unless the SDM fails on me, it is an highly recommended lens from me. It is the best that I have used.
Out of all the funky and odd ball manual lens that I have tried, used and swapped from one to the next wanting to find something that is similar to the DA*, there isn't any that come close. But I have to say that when I want something smaller that does most the job that my DA* zoom does, the cheap
Vivitar 70-150mm f/3.8 from Kiron in 2-touch zoom is what I will recommend as a knock-out cheapo m42 lens that I can always rely on as a backup to the DA* zoom with a small form factor and weight. I also find the
Kiron matching 2x multiplier of great value that add flexibility for the lens into 140mm - 300mm lens.
That Kiron lens is quite sharp even wide open and it has a beautiful focal range for portraits. Had it started at 50mm like the DA*, it would be a no brainer to get by the dozens and kept them as gift for buddies.
Some recent test shots in wide open f/3.8 aperture indoor
1/60 sec, f/3.8, 150mm, iso 400, 0 Ev
off-focus as I aim at the mouth
1/50 sec, f/3.8, 150mm, iso 400, 0 Ev
1/50 sec, f/6.3, 70mm, iso 400, 0 Ev
1/40 sec, f/8.0, 70mm, iso 200, 0 Ev
1/60sec, f/8.0, 70mm, iso 160, 0 Ev
Vivitar 70-150mm f/3.8 from Kiron in 2-touch zoom