Calculate total magnification by dividing the focal length of the objective by the focal length of the eyepiece, as noted above. Detail of moon, planets, close double stars. Requires better than usual viewing conditions. Type of telescope used by Galileo. Provides the highest quality images aperture for aperture.
Images are crisp and well-defined even at large magnifications.
Best choice for observing high resolution objects such as double stars, small details of planetary features, globular clusters, small faint galaxies. Low power eyepieces widen field of view. May require an altazimuth mount to be affordable. If any part is made of plastic, buy legos instead. But the better refractors give razor-sharp images.