qqphotos
Well-known
The Summitar has a terrible barrel distortion, at least mine does. There should be a thread about the Summitar sometime.

Untitled by eric volpe, on Flickr
I prefer the Summicron too, especially at wide apertures, but I haven't noticed much distortion - I wonder if there was a change in design at some point in its manufacturing life? I've seen other people mention it too. Mine is a 10-blade coated one from 1949 and if anything this example shows a small bit of pincushion.