This particular 105mm f2.8 is actually quite a nice, compact lens. It has pre-set apertures and as the usual with pre-set apertures, it's circular at any aperture. This lens also seems to have multi-coating. In actual use, it's quite nice. The lens is well made and focuses smoothly. My copy has a T-Mount to M42 mount installed.
The lens is reasonably sharp wide open, and it surprises me with its sharpness when stopped down. At f8, the lens is very sharp. The bokeh looks nice to me, no doubt helped by the circular aperture blades.
Would you buy one? The 100-105mm lenses don't seem to be very popular focal lengths. Personally, I like it just fine, especially my Canon EF 100mm f2 and EF 100mm f2.8 IS, both are exceptionally good lenses and great as a portrait lens on full frame. The 105mm focal length gives you just a bit more reach and nice, tighter head and shoulder shots, than the 85mm, which for some reason, always seems to be way more expensive than other portrait focal lengths. As for the Soligor 100mm f2.8, I think $10 is a good deal, and even $20 is still ok. I think it would make a nice portrait lens.
Bokeh - Sony NEX-6 & Soligor 105mm f2.8 @ f2.8. Click for larger.
Window Seats - Sony NEX-6 & Soligor 105mm f2.8. Cick for larger.
Untitled - Sony NEX-6 & Soligor 105mm f2.8 @ f2.8. Click for larger.
The power of nature - Sony NEX-6 & Soligor 105mm f2.8. Click for larger.
Cleaning up - Sony NEX-6 & Soligor 105mm f2.8.