Since there is excellent optics readers on this forum, I am curious if someone can help me with this question. It is somewhat related to LF, as this same issue can be applied to photographic lenses.
I am having lenses made with a dual element design, for a stereo viewer. One singlet and one doublet in a barrel. The effective fl of the pair is 45mm. However, I need to determine the EXACT effective fl of each set up in a barrel, so I can pair them to match. I can alter the fl by changing the distance between the two elements.
I was trying to find a means to test to accurately test the fl, better then .1mm accuracy. I would assume this would involve using a secondary optical instrument, such as a microscope that looks through my lens to a focus target. Adjust microscope till it's in focus, then measure the focus travel the microscope made to acheive focus, use this distance on a look-up chart, which was prepared with test lenses of known fl's.
Or, maybe I am completely off and there is some other simplified method? Any help would be greatly appreciated. Oh, and I am trying to keep the aparatus under $5k, which would rule out expensive optics analyzers. TYIA