Fitting it all together

How do all these optical gadgets attach to the telescope? Figures 5.4-5.7 show a few of the most common kinds of adapters. The key to all of them is the T-ring or T-adapter that attaches to the camera body. Originally designed for cheap "T-mount" telephoto lenses in the 1960s, the T-ring is threaded 42 x 0.75 mm so that other devices can screw into it, and its front flange is always 55 mm from the film or sensor.

T-rings differ in quality; some are noticeably loose on the camera body. All contain small screws that you can loosen to rotate the inner section relative to the outer part; do this if your camera ends up upside down or tilted and there is nowhere else to make the correction.

1V4 or 2

inches

Eyepiece tube adapter

Car T-ad

Car T-ad

Figure 5.4. Simplest camera-to-telescope adapter fits into telescope in place of eyepiece.

Threaded 42 x 0.75 mm

Figure 5.4. Simplest camera-to-telescope adapter fits into telescope in place of eyepiece.

24 threads per inch

Figure 5.5. Schmidt-Cassegrains have a threaded rear cell and accept a matching T-adapter.

24 threads per inch

Figure 5.5. Schmidt-Cassegrains have a threaded rear cell and accept a matching T-adapter.

Rear cell of telescope or 2-inch tube Focal adapter reducer

Telescope T-adapter or off-axis guider

-vwp

Figure 5.6. Meade or Celestron focal reducer screws onto rear cell of telescope.

You can get a simple eyepiece-tube adapter that screws into the T-ring (Figure 5.4) or a telescope T-adapter for other types of telescopes (Figure 5.5). Here you'll encounter the other screw coupling that is common with telescopes, the classic Celestron rear cell, which is 2 inches in diameter and has 24 threads per inch. Meade adopted the same system, and telescope accessories have been made with this type of threading for over 30 years. In particular, that's how the Meade and Celestron focal reducers attach to the telescope (Figure 5.6).

If your telescope doesn't have Celestron-style threads on its rear cell, or you're using an electric focuser that makes them inaccessible, then Meade's

Figure 5.7. One way to use a Meade or Celestron focal reducer with a telescope that lacks a threaded rear cell, or with a 2-inch-diameter electric focuser.

Field of view (angle of view)

Aperture diameter

Field of view (angle of view)

Film or sensor

Focal length

Figure 5.8. Every telescope or camera lens has an aperture, a focal length, and a field of view.

Film or sensor

Focal length

Figure 5.8. Every telescope or camera lens has an aperture, a focal length, and a field of view.

"SC accessory adapter" (Figure 5.7) comes to the rescue. It has the appropriate threads and fits into a 2-inch-diameter eyepiece tube or focuser.

Besides these common adapters, there are also adapters for many other configurations; check the catalogs or Web sites of major telescope dealers.

Digital Cameras For Beginners

Digital Cameras For Beginners

Although we usually tend to think of the digital camera as the best thing since sliced bread, there are both pros and cons with its use. Nothing is available on the market that does not have both a good and a bad side, but the key is to weigh the good against the bad in order to come up with the best of both worlds.

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