Hi
I must have gone through five Summitars and each was unique. One had the tendency to distort at the corners- for instance, pictures of grouped people would have those at the sides seem to lean towards the centre. Must be due bad lens repair, but I've seen this "look" in old pictures from the 1950s.
Like what the others said, the Summitar seem to be soft at full aperture. They go fine at around f/4. Personally, I don't find them spectacular or interesting. The Jupiter-8 and Canon 1.8 seem to do better at bigger apertures- and at almost any setting for that matter.
I've kept two- a war-time uncoated version with the 'old-style' f-stops (2, 2,2, 3,2, 4,5...) whose smallest f-setting is f/12,5 but its aperture blades actually move beyond this mark for some unmarked, smaller f/ size. This lens came with a war-time Leica IIIc. Another Summitar is a coated 1950s which I keep for the sake of having one... 😀
The uncoated Summitar is very interesting. It shoots with low contrast, but otherwise does OK, even for colour. See attachments below.
Then, I read somewhere that there were Summitars marked with an "*". These were supposed to be Summicrons.
🙂
Jay