How Telescopes Work

Other Accessories

Dew Caps

Because you will observe during the night, when it is probably cooler, moisture can condense in your telescope and on the optics, which is more of a concern if you have a telescope with an open tube. To prevent this, you can use a dew shield, which wraps around the front end of the telescope. The shield extends the length of the tube and allows moisture to condense on the inside of the shield, rather than in the tube. Some shields can be heated to prevent moisture from condensing at all. Dew caps can range from $30 to $100. Heaters, which are usually powered by 12-volt DC batteries, consist of electrical heating strips or hand-held, "blow gun" dryers (like portable hair dryers). Heaters can range from $15 to $50 (battery not included).

Observing Table and Chair

Astronomers carry many things with them (eyepieces, filters, star charts, red flashlights, field guide, etc.). It is often helpful to have a level surface on which to lay these things out. Many astronomers will carry a folding card table or tray table. Astronomy suppliers have made special tables with non-slip surfaces that roll up compactly for storing in a car's trunk. These tables cost around $50.


During a long night's observing, you can be uncomfortable standing all of the time. When looking at objects high in the sky, a refractor's eyepiece end is low to the ground. So you may need a chair, such as a folding chair or folding camper's chair. Again, astronomy suppliers have made special observing chairs and stools that fold up and are adjustable. They can range from $40 to $150.

Astrophotography Accessories

Astrophotography is a favorite pastime of many amateur astronomers. Photographs of deep-sky objects, the moon and planets can be taken with conventional film cameras, CCD devices/digital cameras, and even video camcorders. Photography can be done without a telescope, with the camera "piggybacked" onto the telescope (i.e. telescope is used to guide the camera) or with the telescope as the camera's lens (prime focus photography). If you wish to do astrophotography using prime focus photography, you will need the following:

  • 35-mm camera (with manual capability), video camcorder, or CCD device/digital camera
  • camera or "T" adapter
  • manual cable release for 35-mm camera
  • off-axis guider
  • lap-top computer or personal digital assistant (PDA) (for CCD use only)

The camera or CCD device acquires the image -- CCD cameras for astronomy can range from $500 to $10,000. The camera or T-adapter ($25 to $80) hooks the camera to the telescope's eyepiece holder. The off-axis guider is a combination camera adapter and eyepiece holder, allowing you to guide the telescope's movement with the object while acquiring the image with the camera. The off-axis guider splits the light coming from the object so that you can look at the object, usually with an illuminated reticle eyepiece, and the camera can capture the light on film/CCD. Off-axis guiders can range from $110 to $150. The laptop or PDA has the software to acquire, display, and store the image; image processing is usually done later, away from the observing site.

In addition to images, amateur astronomers can measure the light from stars using photometers to do various scientific investigations. Photometers, like CCD cameras, can range from $500 to $10,000, depending upon the type.