Re: [Goptical] entrance pupil determination

[Aaron Webster]

Thanks for the quick reply. The problem I see with set_entrance_pupil is that it assumes you've chosen it correctly. It just assigns whatever surface you send to it as the entrance pupil, even if that's not correct for your system.

It doesn't look like goptical does this for you, perhaps Alexandre knows better.  I'm not sure that it would make sense, anyway -- I've never encountered such a calculation (but then again I'm no expert).

Looking at the Tessar lens design, since the stop is behind the first two lenses, and it limits the rays passing through the system, the entrance pupil is just the image of the aperture stop.  So if you consider the focal length of the first pair of lenses and the distance from them to the aperture stop (you do), you should be able to compute this directly.

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Aaron Webster