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I'm using this lens on NEX 5N with an OM adapter. This lens is very well built, though heavy and big. It's a one touch varifocal zoom, meaning the focusing changes when you zoom. Some people hate it, I love it. One of the advantages of varifocal lens, it can focus from a distance of couple inches. I like smooth and precise focus/zoom ring.
Unfortunately, this lens is noticeably softer and has less contrast wide open than my other manual zooms in this range (I'm comparing to Minolta 35-70/3.5 and Canon 35-105/3.5). It also has softer corners. It gets better at F/5.6-8, but never catches up with the other. The bottom line - a very convenient lens, but the image quality is just average.
The Kiron lenses, made by Kino Optical, have been "cult" favorites in Japan for many years. They made several of the Vivitar Series 1 lenses, in addition to those badged under the Kiron name. This lens is of excellent quality, with a build and image quality equal to comparable Canon optics. The lens is heavy, smooth in operation, and very good looking, if that counts for anything. The only caveat concerns lubrication issues. The diaphragm may be frozen, due to old lubricants going gummy/solid. A good cleaning will result in a great performing lens that will last for many years with modern lubricants. I'd advise anyone to buy and try this lens. I don't think you'll regret it. I'll post a pic when my batteries recharge on the p&s.