Ken: yes, it's very important for the type of lab setups those are typically used in.


Henrim: I didn't do a tolerance analysis but if I had to guess I'd say keep the airgaps (lens seats) to within at least +/- 0.010" and even better to be within +/- 0.005". That's very easy to achieve when machining the barrel on a lathe.


Stop before or after the second lens: stop position impacts some of the Seidel aberrations such as coma, astigmatism, etc, and was selected based on what gave better performance.

Generally speaking, the ideal position for the general positive-negative-positive design form is centered, maintaining design symmetry. Physical necessity, however, requires offsetting the stop position to one side or the other of the negative lens.