Markings on my 12" Dagor

[Tedd]

I have a 12" Dagor Gold rim serial# 772802 and there are some markings etched on the rim of the rear element.
I use this lens for 2:1 portraits on my Wisner 12x20. And some landscapes, but it barely covers.
"EF 302.7"
"BF278.4"
"ND 5.95"

What do these mean?

"EF 302,7" I am guessing might be the effective focal length?

[Mark Sawyer]

Yep, you got it, 302.7 mm as opposed to 304.8 or something if it were exactly a 12" lens, as opposed to just close enough to call it a 12" lens...

BTW, Tedd, you should choose the wording for your headings more carefully... "Markings on my 12" Dagor" sounds vaguely pornographic after a couple of beers...

[Struan Gray]

EF: effective focal length.
BF: back focal length: distance from apex of rear element to film plane when focussed on infinity.
ND: my guess: nodal seperation - the distance between the front and rear nodal points.

[Jim Galli]

Indicates in a former life it was used for photo reproduction. Those were important numbers to those guys.