Thanks, I did my measurements with a 50 mW green laserpointer, just on the floor! the laser on a couple of books to get the right hight...the board is a piece a plywood...
the eyepiece was held in place with a counterweight...
when you held everything in place and square this method is very accurate.

With 50 mW laserpower you can easy see the various lensses inside a optical system, some are cemented, others absorbs
more light, some lensses are thin or very thick.

Holland (real name: Gerrit

)