Different telescopes traditionally have certain mountains that best suit there application and use. The larger Newtonian telescope is difficult to balance on a tripod and needs a solid structure to minimise vibration and movement. Delicate refractors with long focal lengths also require a steady mount and smooth transition in the movement.
Tripod mounts vary in complexity and simplicity which also determines its ability to track the movement of the stars. A simple fork mount can be horizontally opposed with limited tracking or be angled to allow the single directional path of the earths rotation. An equatorial mount is designed to be polar aligned and horizontal the plane of the earth to also allow the single axis of movement to follow the celestial objects.
Dobsonian mount
Refractor telescopes are what most people think of when they talk about telescope design. Light entering the front of the scope passes through an objective lens made with a determined convex shape to direct light to a point at the rear of the scope. This is known as the focal point where the light rays converge before beginning to spread out again. The eye piece is placed just behind the focal point where the light is magnified back into a straight line where the eye can see it. By moving the eyepiece closer or further from the focal point, the image can be focused for the eye relief
The greater the aperture of the objective lens, the more light that can be collected into the telescope making the image brighter. Refractors rely on the use of good quality lens to limit distortion and corruption of the light source. This can make the telescope very expensive as the grinding of lens is often time consuming and the special glass made in small quantities. This type of telescope is best used for viewing small bright objects such as planets and star clusters.
Equatorial mount
The equatorial mount has two axis of rotation; the right ascension and the declination. The right ascension is the angle between the horizon and the zero point on the celestial equator. This angle is measured by fixing the zero point to a known celestial object which is in the constellation of Aries where the Sun crosses the celestial equator at the March equinox. This angle is measured in hours, minutes and seconds with 24 hours being the equivalent of a full 360 degree circle.
The declination is the measurement in degrees north or south of the equator. Points north of the equator are positive and south are negative. Whereby the north celestial pole is +90 and the South celestial pole is—90 degrees. If you were to stand at either pole this point would directly over head. As you move back towards the equator, the pole moves towards the opposite horizon, i.e., if you move north from the South Pole the point above your head would move towards the south until you reach the equator where that point would be at the horizon (-90 degrees). There fore knowing your latitude allows the declination to be set to point directly at the celestial pole.
Once the declination is set and the tripod is level, the right ascension axis should align with the equator and rotate in line with the stars. When a stepper motor is attached to the axis as a drive, the telescope win track an object without needing to continually make adjustments. With the introduction of electronic—computerisation, fork mounts are commonly used with GPS navigation to locate your declination, position, altitude and errors in the tripods level and can not only track objects but find them from a data base.