Meade 90mm Telescopes

Points to Ponder When Buying a Meade 90mm Telescope

Ever since Hans Lippershey applied for the first patent for a telescope in 1608, people have been using these devices to gaze at the evening sky and more. More specifically, many people have used Meade telescopes ever since John Diebel started Meade Instruments as a mail-order business that provided telescopes in 1972. People buy telescopes for a variety of reasons including for giving as gifts, for their own personal enjoyment, and to use with groups of youth or adults.

A telescope is a light-gathering device that gathers light and focuses that light into an image. The instrument's ability to gather light depends on its aperture, optical quality, contrast, and alignment. Generally, the larger the aperture, the more light that is captured. Telescopes with clear glass and reflective mirrors allow light to pass from the lens to the eyepiece. Telescopes that are darker on the inside may make objects appear brighter. Instruments that are aligned properly allow the most light to pass through them.

There are three general types of telescopes. They are:

• Refractors: All refractor telescopes use a curved mirror at the back of the main tube to gather light. These telescopes can be further divided into apochromatic, which are specially treated to bring two wavelengths into a single focal plane, and achromats, which use a special achromatic lens to correct for chromatic aberration.
• Compound: These telescopes usually have a correcting plate connected to the front and back of the tube to take care of chromatic aberration. The plate is then affixed to a secondary mirror.
• Catadioptric: Sometimes called hybrid telescopes, light enters these telescopes through a corrective lens before it hits a primary mirror to be sent to a secondary mirror to be seen through the eyepiece.

While almost any telescope will let you see a vast array of items, the amount of available magnification affects the item's brightness, allowing the user to see details clearer. In order to find the useful magnification, divide the instrument's focal length by the focal length of the eyepiece. For example, if the telescope has a focal length of 1000 millimeters and the eyepiece has a focal length of 25 millimeters, then the telescope has a useful magnification of 40. Many telescopes have changeable eyepieces, allowing you to change the instrument's magnification. See the manufacturerEUR(TM)s site for details.

The aperture of a telescope is the diameter of the main lens or mirror of the telescope. Finding the square of the aperture will give you the light-collecting ability of the telescope and will allow you to compare different makes and models.