I have used some excellent zoom binoculars, but I would not recommend them for astronomical use. While the quality can be excellent, they are (for good ones) both quite expensive, and tend to have relatively small objectives. Instead, for astronomy, go for something in the 60 or 70mm range (preferably, though you could easily go with lower), and not too high magnification (10-15x should be fine). 20x80 would work, but keep in mind how big/heavy they would be. If that isn't a factor, they would be a decent choice.

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