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Don't know if this has been answered before but I measured the exit pupil of my Russian 2.3X40s and found it to be around 8.5mm. I say "around" because there is no hard field stop. If the objective is 40mm and the actual magnification is 2.3X shouldn't the exit pupil be 17.4mm?

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A Galilean system has no exit pupil as such. However large is the eyepiece's aperture, that is the diameter of the "exit pupil". The 8.5mm you measure is the clear aperture of the eyepiece's rear element (I think, and will have to check). At any rate, this clear aperture was clearly chosen because virtually no one's pupils expand larger. Moreover, because the observer's pupils must be well centered on-axis for good performance, the smaller eye lens ensures that this is more easily achieved.

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Home-made 11X50 right angle bino, 8.1 deg. FOV
Modified 26X100 bino, 3.5 deg. FOV

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