old E.Krauss's F

[daytona]

I got a Anastigmat Zeiss 1:6.3 F 250mm By E.Krauss recently. The number on barrel:256; 128; 64; 32; 16; 8; 4.I guess where "256" looks like "F 6.3"(open). Who tell me that the corresponding F value?
Thanks
Daytona

[Steven Tribe]

There is a useful table here on this website.

Table of older aperture systems
Scanned by David Stein

This is a product developed by Zeiss and the "reverse" scale is the one used by Zeiss early on.
Your lens is a Serie II Zeiss Protar size 6 which covers more than 13x21cm. The Krauss versions have a good reputation.

[daytona]

There is a useful table here on this website.

Table of older aperture systems
Scanned by David Stein

This is a product developed by Zeiss and the "reverse" scale is the one used by Zeiss early on.
Your lens is a Serie II Zeiss Protar size 6 which covers more than 13x21cm. The Krauss versions have a good reputation.

Thank you for your help.
Daytona