Telescope eyepieces with a focal length of 10-20mm are generally medium magnification eyepieces. As a rule of thumb, we recommend 25x magnification/inch of aperture for planetary astronomy, and 50x magnification/inch of aperture for deep sky astronomy. If you need help calculating field of view, or magnification, reach out. We're always happy to help. We also have an excellent guide on how to choose eyepieces here.
