Magnifications in the range of 15x - 30x per inch are more commonly used. Therefore, usable magnification depends on the diameter of the objective. Buy the largest diameter objective you can afford. Telescope Selection Binoculars Often overlooked for astronomical use, binoculars provide an opportunity to explore the night sky with low magnification and wide field of view. They are especially suitable for large nebulae, open star clusters and bright comets.
Low magnification prohibits their use for planet study.
The relatively small size and weight provide excellent portability. Most commonly found with 20x-25x magnification, higher priced models may include variable magnification. 60 - 80mm objective diameters are readily available. Even 20x will require a tripod to steady the image for observing. The table-top tripod usually sold with spotting scopes seldom permit tilting high enough to observe objects in the sky.