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I have since looked up the pupil on Wikipedia, which claims a maximum range of 9mm in exceptional cases. So if 7mm is the maximum in normal cases (to say nothing of aging or using belladonna), then...

That's all very interesting, and my apologies for taking the thread in another direction. I just thought that maybe there might be some known examples. Maybe it's a typo, but 7x50 binoculars would...

Thanks for your comments. I have seen higher-power star-gazing binoculars for sale, 25x100 from your example, but this exceeds the power squared to diameter ratio I am talking about. 25x would...

Thanks, but what I would like to know is if there are other binocular formats that exist following the 7x50 and 5x30 examples, whereby the square of power is less than diameter in mm of the lens. ...

A slightly off-topic question about astronomical viewing with binoculars. I once read that ideally, the square of the power of the binoculars should be under the stated diameter of the lens elements...