Choosing and Using a Telescope

What are the types of telescope you should consider?

Spotting scopes look like one half of a prism binocular. They provide a right-side up, left-to-right image. Spotting scopes are extremely portable and usually provide a sharp image with magnification of up to 60 power. The image is right side up and correct left to right. If mounted on a full-size camera tripod, this is an ideal telescope for home or apartment, viewing wildlife across the lake, etc. It just doesn't look so impressive!

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Refracting telescopes uses two lens groups: an objective (in the front) and an eyepiece (in the back). The bigger diameter of the objective, the brighter the image. In small sizes (up to about 3" or 85mm diameter), they are affordable and yield a sharp image.

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Reflecting telescopes "do it with mirrors". A large concave mirror at the back of the telescope is the primary optical element. Because it's difficult to make a good refracting telescope more than about 3" in diameter at a down-to-earth price, we recommend Meade's 4.5" reflector scope for serious amateur astronomers. Conventional reflecting telescopes are a poor choice for terrestrial observation. You look into the scope, near the front, at a right angle.

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Catadioptric telescopes combine mirrors and lenses to give the light-gathering ability of a large mirror combined with a compact size. Eyepieces or cameras are at the back of the scope. A variation of this is the Maksutov Cassegrain design, such as the Meade ETX.

Astronomical telescopes make upside-down images. Astronomers don't care, but when looking at things on this planet it's a pain.
Two types of accessories help:

  • a 90 degree prism turns the image right side up - but flopped side to side.
  • A 45 degree prism or roof prism turns the image right-side-up and correct from right-to-left.

About telescope size: Bigger is better. There are four types of measurements

  • Objective diameter - how big around is the lens that lets in the light, or the mirror that gathers light. For serious use, any telescope with a diameter less than 60mm is unacceptable.
  • Eyepiece diameter: Bigger eyepieces (1.25" instead of .96") offer a step up in quality, brightness and sharpness. The quality isn't determined by the diameter, but manufacturers don't bother making good small-diameter eyepieces.
  • Objective focal length: when no eyepiece is used, at what distance from the objective would an image of a distant star be in focus?
  • Eyepiece focal length. The shorter the focal length of the eyepiece, the more magnification provided - but that leads to loss of sharpness and brightness.

Magnification or power refers to how much bigger (or closer) something looks through a telescope. It's easy to compute: divide the objective focal length by the eyepiece focal length. For example, a 900mm telescope with a 25mm eyepiece yields a 36X magnification

I find that for viewing images on earth, or looking at the moon, 28X is plenty! Some makers promise high magnification in order to sell telescopes, not to give sharp images.

Telescope mounts: a sturdy tripod is important. At even low magnifications, the wind or the beating of your heart can cause considerable shakiness.

  • The alt-azimuth mount swivels freely but provides precise control in one dimension.
  • The more expensive equatorial mount gives precise control in two axes. It can be aligned with the plane of the ecliptic and is geared so that you can follow the apparent motion of a star or planet all night long.
  • New Digital Control mounts use electric motors and electronic controllers to aim a telescope precisely and allow it to follow the apparent motion of a star or other heavenly body all night long. More advanced models may include an Autostar Controller that features "go-to" capability. Once you have aligned your scope to the North Star, you can enter the number of the object into the controllers key-pad and the scope will slew across the skies until it finds it. It's like having a trained astronomer to show you the way!

Accessories:

  • Camera adapters allow you to mount your 35mm SLR camera on your tripod, giving the equivalent of a very long telephoto lens. Most adapters provide a universal thread which requires a "T-Mount" for the specific camera model. We've got them at Chris' Camera Center.
  • Eyepieces:
    • "Short" eyepieces (12, 9, 4mm, etc) provide higher magnification. They also reduce the light and the field of view.
    • "Broad field" eyepieces (25mm, 40mm) let you see a wider area. The image is much brighter and sharper, but things look smaller.
    • Barlow lenses are like teleconverters on cameras. They go between the eyepiece and the telescope focusing tube to increase magnification
  • The 45-degree erecting prism turns the image right-side up and correct right-to-left. Perfect for observing things on our own planet, and almost essential for tracking fast motion. They also let you stand or sit comfortably for viewing.
  • Clock drives turn your equatorial mount scope so it stays lined up on a particular celestial object all night.

Meade ETX-90EC Maksutov-Cassegrain Astronomical Telescope and Spotting Scope now has built-in computerized drive system.

Most good telescopes are too big. Most small telescopes aren't very good. Meade's ETX-90EC goes anywhere and presents the finest optical images - bar none - ever made available in an ultraportable telescope.

It's a thing of beauty, too. Go to our Meade ETX page

New flat-rate shipping program: Any items up to 5 pounds delivered anywhere in contiguous 48 states for $5.49 (ground delivery, UPS or USPS)

Chris' Camera Center, South
150A Laurens Street SW
Aiken, South Carolina
803 641-0501  e-mail us