Today I tested a lens, from I think the 1980s, made by sigma. I am in Holland for my holiday’s and yesterday when I was in Leeuwarden I finally got lucky and found a store where they sold several vintage lenses. I bought 3 lenses with m42 mount and one of them was this sigma 70-150mm f3.5 lens. I immediately liked this lens because the way it looks. It has the little ring to put it in macro mode where it moves the lens forward. It has the typical lines on the barrel for the depth of field settings and a zoom and focus ring in one. The aperture is a constant 3.5 which is not bad and it feels good and solid in the hand. I couldn’t find much information online besides some bad reviews on the pentaxforums.
For me the image quality is not bad as long as you don’t look to close. It focuses easily and most of the pictures where sharp. If you go for ultimate image quality you shouldn’t go for these old lenses, you should buy a moderns lens that will cost you thousands of dollars. But for the 15,- USD I spend on this lens I have probably 90 per cent of the fun taking pictures compared to the modern lens for a fraction of the cost.