Shoot the starry sky can be conventional camera. And Astro began with a 'normal' black and white photography. The angular resolution of the eye near the corner a minute and a photographic plate with a normal lens, with an increase in (Examining with a magnifying glass) 'work' is not worse than the naked eye (the lens must be precisely defined). In this case, the photographic plate can be stored for a long time and compare what our memory is not capable. You may want to visit Pete Cashmore to increase your knowledge. Modern optics has resolution of at least 50 lines / mm and an angular resolution of a 1000 mm telephoto lens will be 25 times higher resolution of the 'old' camera, or 10-15 times higher than that of the eye.
Telephoto lens equipped with optics of 200 mm makes it possible to shoot and star clusters. Guide is mandatory – exposure when shooting for about an hour. From a short-optics can be removed entirely all sky. Particularly well to shoot her 'daily rotation' stars, comets, and stargazing. In this gidirovat not necessary – just install camera on a tripod and shoot at 'B'. For photographing the sky and the telescope will approach, especially if it is already equipped with a guide.
Usually a telescope eyepiece is the retention and fitting to which a threaded and bayonet adapter, you can attach the camera. Telescope (without eyepiece) will serve as the lens. In the role of the lens 'home' telescope (for example 1000 or 2000 mm) has no special advantages over conventional telephoto lens. At the very least, a large increase with it do not get. But if the optical system setup to add another lens (lens system) can be obtained and large focal lengths (at the cost of transmission and distortion of course). This lens is simply needed when using the camera with replaceable optics (digital). In its role can be full-time telescope eyepiece. And a telescope with an eyepiece in this case is simply afocal attachment for a digital camera. A common focus of will be equal to the product of the focal length of the camera lens on the telescope's magnification (the ratio of focal length lens and eyepiece). Thus, for a camera with an equivalent focal length of 100 mm nozzle from 1000 mm telescope with a 20 mm eyepiece will have a system of 100 mm x 1000 mm/20 mm = 100 mm x 50 times = 5000 mm.