2f, t'isn't brillig now and t'wasn't brillig yesterday. There are no snarks in the neighborhood, although I do have a jar of boojum jelly in the pantry. The boojum isn't as dangerous as Carroll reported.

2f/2f has a little significance in photography. The minimum film-to-subject distance is 4f plus the lens' internodal distance, which is usually neglected. 2f from film to the lens' rear node, 2 f from the lens' front node to subject at 1:1. Thanks for explaining that you were being cute in a submersible, not a close-up, way.

I quoted you. Why do you think I didn't?

And where is it written that 210 mm is the standard focal length for 4x5? I think you made it up.