A 50mm telescope, referring to the aperture size of the telescope, is typically a small, entry-level instrument. Such telescopes are often compact and portable, making them ideal for beginners or casual observers. With a 50mm telescope, you can observe celestial objects like the moon, with its craters and maria, and some of the brighter planets like Venus, Mars, Jupiter, and Saturn, though with limited detail. You may also be able to view a few prominent star clusters, bright binary stars, and some of the most luminous deep-sky objects, such as the Orion Nebula. However, due to its small aperture, a 50mm telescope has limitations in resolving fainter and more distant objects. It may struggle under light-polluted skies, so a darker observation site would be beneficial to maximize its potential. Overall, it is a great starting point for hobbyists interested in astronomy.