This refractor telescope has a simple altazimuth mount
A refracting telescope uses a large lens (called an objective lens) to collect and focus light. Refracting telescopes (commonly called refractors) are able to focus light because of a phenomenon called refraction, the bending of light rays when they pass from air through a denser medium such as glass. An eyepiece magnifies the tiny images formed by the objective lens so that they can be viewed by an observer. The light-path of refracting telescopes is direct and unobstructed, an advantage that enables them to produce images that are generally superior in quality to those of reflecting telescopes.
Instructions
1. Assemble the telescope according to the instructions in your owner's manual and familiarize yourself with the parts, their names and functions. Basic assembly of most telescopes involves attaching the optical tube to the mounting and the mounting to a supporting tripod or pier. Two types of mountings are commonly used by refracting telescopes: the altazimuth type that has no polar axis, and the more complex German equatorial type.
2. Examine the eyepieces provided with the telescope. The eyepieces are the short tubes that have an eye lens at one end and an open, polished steel barrel at the other end. Most telescopes come with two or three eyepieces.
3. Select your lowest-power eyepiece. The power (magnification) of a telescope is determined by the objective focal length and the focal length of the eyepiece. The eyepiece focal length is the number followed by "mm" (millimeters) etched near the eye lens. Telescope power is inversely proportional to eyepiece focal length: the shorter the eyepiece focal length, the greater the magnification produced by the telescope.
4. Turn the thumbscrew at the end of the focuser drawtube until the eyepiece barrel fits inside. Insert the eyepiece and tighten the thumbscrew using moderate tension.
Align your line-of-sight along the telescope's optical tube, then point the tube toward a distant object by moving it as necessary on the mount's axes.
5. Look in the eyepiece and turn the focuser knob to produce the sharpest image. Fix an object in the center of the field of view and tighten the mount locks to secure the telescope tube.
6. Look in the eyepiece of the small finder scope and turn the thumbscrews on the finder scope's mounting, adjusting the image until it is centered in the field of view. This becomes easier with experience. The finder produces a low magnification; but it has a much larger field of view than the telescope, which makes it highly useful for locating and centering objects in the main telescope field.
7. Determine the telescope magnification by dividing the objective focal length by the eyepiece focal length. For example: if the objective focal length is 1000 mm and the eyepiece focal length is 10 mm, then the telescope magnification is 1000/10 = 100 x.
The objective focal length is usually etched on the objective lens housing.
8. Determine the telescope field of view by dividing the eyepiece's "apparent" field of view by the telescope magnification. For example: if the eyepiece apparent field of view is 50 degrees and the telescope magnification is 100 x, then the actual field of view is 50/100 = 0.5 degrees (the apparent diameter of the full moon). Eyepiece apparent fields of view are often given in the owners manual, and are always available from the eyepiece manufacturer.
Tags: focal length, field view, eyepiece focal, eyepiece focal length, objective focal, objective focal length