Optical Features of Telescopes

The ability of a telescope to focus light is related to the optical features you use. Considerations to make when purchasing optical equipment Aperture, Magnification, Focal Length, Focal ratio, Wave Number, and Resolution. If you purchase low quality merchandise, you won't be able to see what you are looking for as well.

The most important consideration is the Aperture. This is the ability to focus light and is related to the size of the lens or mirror that is used. In other words, the bigger the lens or mirror, the brighter the final image. The biggest telescope, however, is not always the best.
Magnification is dependent upon the lenses used and the distance to the eyepiece. A general rule of thumb to follow is 40-60x per 1 inch of aperture. Usually low magnification gives the best light.
Focal length is defined as the optical length of the telescope lens. Long focal lengths usually mean higher magnification. Don't mistake the length of the telescope for focal length though. Some compound telescopes light paths are folded and become longer in a short tube.
The focal ratio tells us about he brightness and width of the field of view. They are divided into three sections. F/10 or higher is good for viewing the moon, planets, or stars. F/8 is great for all around viewing. F/6 and lower is meant for viewing deep sky objects.
The wave number is also known as the wave error. It tells us how good the mirror or lens was ground to an almost perfect surface. The smaller the number, the better the lens or mirror. The minimum number that is acceptable is one fourth. The performance is in the accumulation of the numbers of each optical piece.
Resolution is the ability to find the details in the moon or a planet. It is dependent upon how well the telescope can separate two close objects. It also rests on the aperture and the observing conditions that are present.