Quote Originally Posted by Steven Tribe View Post

There are plenty of paired numbers on both the usual lenses and a double pair on the achromat. I think there is a good deal of "assembly" logic in writing actual focal lengths on lenses or combinations (Rear pairs). I am sure they could grind and polish accurately, they had to work with glass that must have had some variation in refractive index.

The numbers on photo 2 are from the rear pair, whilst the two sets on photos 3 and 4 are both from the Achromat.

The future project in "nailing the lens markings" could be a separate thread?
Looking at these numbers, no focal length combination that could work to come up with a total focal length that is reasonable in light of the size of the lens, so yes, this will need a separate thread ... the two digit numbers are killing that thought for now ...

Cheers,