Two good eyepieces are enough to get started: one with a medium focal length for wide fields of view and locating objects, and one with a short focal length for the Moon and the planets. The magnification is calculated by dividing the telescope’s focal length by that of the eyepiece: on a 150/750 Newtonian, the Hyperion 17 mm gives 44× and the Hyperion 5 mm 150×; on a 200/1200 Dobsonian, these same magnifications yield 71× and 240×. Our guide Choose an eyepiece explains the calculation in detail.
No: the planet remains in the center of the field of view, so a field of view of 60 to 70° is more than enough. What matters is sharpness and a comfortable eye relief. A Barlow 2× Tele Vue Doubles the life of your existing eyepieces for less than the cost of a new one.
In theory, about twice the diameter in millimeters: 300× for a 150 mm object. In practice, atmospheric turbulence often limits magnification to 150–250× in Switzerland, regardless of the instrument. A smaller but sharp image shows more detail than a large, blurry one.
For the Moon, a lunar filter reduces glare and brings out the texture. For nebulae, a UHC filter such as the'Antlia UHC Pro Significantly enhances contrast, especially with a Dobsonian telescope. It has no effect on galaxies or star clusters.
A 2″ secondary mirror is compatible with wide-field eyepieces and, with an adapter, 1.25″ eyepieces; a dielectric secondary mirror reflects more light than an aluminum-coated mirror. The 2″ Askar Elbow Fitting is a good choice for a refractor or a Schmidt-Cassegrain telescope.
