Part of the Zeiss combine was the glassmaker Schott, who worked hand-in-hand with the lens makers. New glass was developed to satisfy new designs, new designs promoted new glass types.

Zeiss design was evolutionary. Since the marketing department never ran the company, the lenses were usually the best they could be in any era, and small improvements were normal. They might not show up in patent literature, for the Tessar patent was, as Kingslake described it, " extremely general ".

My newest Tessars, souvenirs from a winter in Prague in the '90s, are almost unbearably contrasty.