What practical magnification ceiling did Galileo find because increasing power drastically shrank his field of view?

Answer

Around 20 or 30 times magnification

Galileo found a practical ceiling around 20 or 30 times magnification, as pushing higher made the image too small to be useful, allowing him to see only about a quarter of the Moon's face without repositioning.

What practical magnification ceiling did Galileo find because increasing power drastically shrank his field of view?
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