I had two Summitars at one time, they were sharp, field flatness was good, micro-contrast was average for a 50-year-old lens (low by today's standards). Biggest downside was the lenses' tendency to flare in backlit situations (in a way, this was acknowledged by Leitz in the way they provided a folding lens shade of huge proportions). I see the 50 mm F2.5 Skopar has 8 elements in 6 groups (vastly different from the old Tessar-based Color-Skopar of the 1950s and 1960s). No personal experience of the new Skopar, I would expect it to nearly equal the Summitar at its best and have much better flare suppression, making it a more versatile all-round lens.
Originally Posted by laz