To find objects in the sky you use two co-ordinates, Right Asscention (RA), and Declination (DEC). The easiest way to imagine this is to think of the Earth being inside a huge bubble. All the stars are attached to the inner side of the bubble and the planets, moon and sun move across the surface. If you then extend the Earths lines of Latitude and Longitude onto the bubble's surface, you can work out their positions. The RA .is equivalent to the skies Longitude and the DEC represents the skies Latitude. The only thing to remember, is that the RA and DEC values are 'nailed' to the stars. The individual co-ordinates of the stars do not change, where as the relative positions of planets, the moon, the sun do.
Due to the Earth being inside this "bubble", the stars appear to move. They are not actually moving (unless you really want to get technical!), its the Earth rotating that makes the positions change. The stars appear to rotate at about 15 degrees per hour around the Celestial pole. If you open the shutter of a camera for more than a couple of seconds, you will be able to see the movement as trailson the photos.
The only way to stop star trailing is to move the camera with the stars. An Equatorial mount is designed to rotate around the Celestial pole at the same rate as the Earth turns. One of the axis on an Equatorial mount (the polar axis) points at the pole star. The mount with the camera and/or scope attached rotates on this axis using RA co-ordinates to measure the distance moved across the sky. Some of the newer scopes come on a Fork mount. To get the correct movement, the mount has to be angled so that it points to the pole star.
The Earth is tilted on its axis by a few degrees. The imaginary line that runs through the centre of the Earth, through the poles, is extended into the sky. The point where this line hits the sky is known as the Celestial pole. All the stars appear to rotate around this point and the pole star (through pure coincidence), is practically at this point. This is only true though for people in the Northern hemisphere.
A Barn door tracker is a simplified Equatorial mount. The basic principle is that two pieces of wood are hinged at one end. The two boards sit up at an angle equal to your Latitude. The hinge points to the Celestial pole and a threaded rod at the other end slowly separates the boards. Some simple calculations are done so that one revolution of the rod is equal to one minute of time. The tracker is very easy to make and the one I made can be found at Steve Tonkin's page. This is really for use in the Northern hemisphere because the Southern hemisphere does not have a bright star near the Celestial pole.
There are a few different types of configurations when it comes to scopes. The two main categories are Reflectors and Refractors. The Refractors (Long John Silver type), are the scope that most people think of when someone says "telescope". They have a lens at the front (objective), and the light passes down the tube. The other end has an eyepiece to focus the light. You change the eyepiece to change the magnification. Although Refractors can be used for deep sky observing, they are better suited for planetary observations. They generally have a long focal ratio which gives better contrast. They do have a lot of benefits. The lens and fixings are stationary and don't need any adjusting (collimation). The tube is also sealed from dust and needs little maintenance. The long focal ratio (around f/10 and up), gives excellent planetary, lunar and binary star images.
The down side to the Refractor is that you are limited to the size of the objective. For deep sky observing and photography, you really need the biggest objective you can afford. The other type of scope are the Reflectors. Also known as a Newtonian, the Reflectors use two mirrors. The primary (objective) mirror is sat at the bottom of a tube. The mirror is ground into parabolic shape and made reflective. The incoming light at the front of the tube is focused back to the front of the tube. Here, it bounces off a flat, secondary mirror. The secondary (diagonal) sits at 45 degrees to the light path. The light from the diagonal is then reflected through a hole in the side of the scope to the eyepiece. To change the magnification, you do the same as with the Refractor, change the eyepiece!
Reflectors are better suited to deep sky observing at large apertures (primaries). Reflectors are cheaper per inch of aperture than Refractors. Reflectors normally have shorter focal ratios (f/4 to f/7). This means that you get less contrast for planetary images, but when it comes to deep sky observing, you get larger fields of view and shorter exposure times for photography. The main problem with short focal ratios, is that collimation becomes a very big problem. This is easy to keep a check on once you have done it a few times.
To get the advantages of the long focal ratios of the Refractor and the larger aperture of the Reflector, the Schmidt Cassegrain scope has been developed. The Schmidt Cassegrain uses a correcting lens at the front of the tube and then passes the light to the primary at the bottom of the tube. The parabolic mirror focuses the light onto the secondary which is in the center of the front lens. The light is then reflected back down the tube, through a hole in the primaries center, and out to the eyepiece. How do you magnify the image? You have guessed it, change the eyepiece.
The scope I own has the Schmidt plate at the front but uses a mirror system identical to the Newtonian. This means that I can have a primary mirror of 8 inches in diameter but the tube length is much shorter with a short focal ratio (f/4). Schmidt Cassegrain scopes are more expensive than Newtonians, but give excellent images over a broad selections of objects.
Basically this means to line the scopes optical axis with the scopes mechanical axis. To get the best light path through the scope, you need to have everything lined up. If the axis are not lined up, images will become distorted and false colours can be introduced into the image. I good page written by Nils Olof Carlin gives a very good explanation on the finer points of collimation.
A sight tube is used in collimation. It is basically made from a 35mm film canister with one end open and a small hole drilled in the other. You place it into the eyepiece holder and use it to line up the optics. The design was found at Nils Olof Carlin web page.
A CCD camera is a digital camera that uses a silicon chip to convert light (photons), to an electrical signal (electrons). The camera is more sensitive than 35mm slide or print film, which means that exposure times are greatly reduced. The only problem with the CCD camera is a DC power source is needed to run the camera, which means carrying a battery around with you. As well as the power source, a computer is needed to control the camera. This means, unless you have a water proof observatory to house a computer, a laptop computer is needed.