When did lens coating started for good at Zeiss?
When did lens coating started for good at Zeiss?
When did lens coating started for good at Zeiss?
Different Zeiss-people published articles about coating at the start of the 1940s. In one of them, published in December 1940, we learn that a process of coating glass was developed during 1935 and a patent applied for. The author then writes (my translation): “Soon after lenses for aerial photography were treated by this process. Lenses and other optical devices thus treated were called “T-Optik” and marked with a red T on the mount . . . . . Zeiss T-Optik was for years only used in the most valuable instruments, but it will now, after it has been tested and fully elaborated, generally be used in any instrument where it could be of benefit” (Note that the author says the red T was used early on. I am here also referring to another thread on this forum about a Tessar and a red dot).
Some lenses were coated later, by Zeiss or by others, but the trouble is that you cannot see whether a
T-lens was coated originally or later, as Zeiss apparently also in the latter case engraved the red T on the number ring. To the best of my belief there is however one exception. Due to excessive flare at small apertures the fast uncoated 1.5 Sonnars only stopped down to 11, but once coated tolerated being stopped down further. So if a regular production prewar 1.5 Sonnar has a minimum aperture of 22, it was originally made with coating. But we cannot conclude the other way round that all coated 1.5 Sonnars with minimum aperture 11 were coated after manufacture, maybe regular coated production started before the minimum aperture was changed to 22. Some writers claim that there was a progression from 11 to 22 through a period when these lenses had a minimum aperture of 16, but I haven’t seen any. There are 1.5 Sonnars with minimum aperture 22 already in the production 2610…(august 39) and many coated Biogons in the production 2672…(november 40). 5cm 1:2 Sonnars are all coated from about no.2684300 (no date).
But all this doesn’t tell us anything about lens no.2370387. This lens has a mount differing from those of the regular production from 1936 to at least 1943. Zeiss undoubtedly coated different lenses to get practical experience, but why would they make a special mount for that purpose? Why not just coat a regular production copy? The lens’ black front rim points to the immediate postwar period, but the serial number belongs to a production of Tessars in 1938! So?
PS: I have a similar “mystery” lens, a coated Biogon where there is ample room for the red T on the number ring, but according to the serial number it is a Tessar from 1937.
