Erik van Straten
Veteran
All Voigtlander lenses are likely to be sharper than the collapsible.
This statement is definetely untrue.
Collapsible Summicron 50mm f/2 @ f/2.
Erik.

All Voigtlander lenses are likely to be sharper than the collapsible.
The later type 1 Rigid Summicrons have improve/harder coatings. The construction also changed lightly. I believe that the earliest Type 1 Rigid Summicrons were slightly different optically from those that follwed, based on taking a 14x apart.
And I agree that there is some "magic" to the Collapsible Summicrons. If you blow up 100% crops, they are slightly softer than the Rigids. I just like the 13x collapsibles better. They are not hard to work on, the Rigids are a real pain.
within the Type 1 Rigid Summicron/ DR Summicron, the Optics Module seemes to have been tweeked early on at ~15x. The later lenses, post ~1960 or so, have better coatings. Probably around the time the Summilux was introduced. Again- I'm not citing official records, just going on taking a few apart.
That is my experience as well. I just repaired a Summicron Ridgid that had THREE elements put in backwards! That tended to reduce its sharpness.