High power eyepieces (e.g. 3mm to 10mm) are used not only for obvious observations of planets and double stars, but can be employed for bright, compact deep sky objects. Not only will the scale of an object like a planetary nebula or globular cluster be impressive as it fills the eyepiece FOV, but the background sky will be very dark as the contrast effect increases with added magnification, provided that the atmospheric seeing conditions are favorable enough to reveal a sharp image. The 4.5mm is a popular choice for a wide variety of telescopes, producing some of the highest magnification views that most astronomers will observe at.
