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How to Use a Computerized Telescope






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> How to Use a Computerized Telescope > Updates and Additional Information

How to Use a Computerized Telescope
Updates and Additional Information

Copyright 2004 Michael A. Covington.
Please link to this page rather than reproducing copies of it.

Content last updated 2006 July 18

Misprints in the first edition

[p. 13, line 10 from bottom] "13 hours" should be "14 hours".

(Thanks to Brian Carrington for pointing this out.)

Additional notes

[Overall] A huge number of new models of computerized telescopes have come out since this book was written just a short time ago. Please do not despair if your telescope is not described in detail. All telescopes work on the same principles.

[p. 48] See the note to p. 53. For more tips on polar alignment, click here.

[p. 53] If you rely on the 90-degree mark on your setting circles when doing polar alignment, be sure to check its accuracy periodically. (I was bitten by this: over a period of about a year, mine developed an error of about 1 degree after previously being practically perfect, and for a long time, I was having unexplained trouble with polar alignment.)

The best way to check is to put the telescope on its wedge, set it to 90 degrees declination (pointing directly away from the base), and view Polaris (which doesn't move appreciably with the earth's rotation) or a distant tree.

Twirl the telescope around its polar axis. The field of view in the telescope should twirl around its center. If it doesn't, move the telescope in declination until it does. Then you've found where the 90-degree mark should be. Loosen the appropriate screw (probably in the middle of the setting circle) and adjust the setting circle so that it reads 90.

If there is some side-to-side error in the telescope mount, you may never achieve perfection, but an accuracy of 0.1 degree is easy to achieve, and well worth it.

[p. 76] The picture at the top of this page does not necessarily indicate a problem with a Schmidt-Cassegrain or Maksutov-Cassegrain -- at least not if the effect is somewhat smaller than shown in the picture.

Catadioptric telescopes normally show slightly different star images inside and outside focus, for a couple of reasons. First, the zonal correction of spherical aberration in these telescopes is fairly complicated, and this test doesn't do justice to it. Second, when you focus by moving the main mirror, you're changing the focal length and thus the correction of spherical aberration.

[p. 96] Since writing the book I've fallen victim to presbyopia and have to wear bifocals. Here are some particulars of interest to astronomers.

Progressive (seamless, "no-line") lenses work better at the telescope than I expected, as long as the eyepiece doesn't have a super-wide field. There is some blur at the bottom of the field, but it's not serious. Naturally, the quality of an eyepiece shouldn't be evaluated while wearing these lenses, but the view is not bad. (My lenses are Hoyalux GP Wide high-index plastic.)

Conventional bifocals are either great or terrible, depending on whether the near-vision segment gets in the way of the eyepiece. Most eye doctors assume that you're going to read a lot, so you need the near segment to be high enough to fill much of the visual field. For astronomy, though, the near segment needs to be 11 mm below the pupil, to stay out of the way. I have had a pair of bifocals made this way, to give me perfect distance vision and perfect vision through the telescope, with a near-vision segment just big enough to enable me to read charts and see the control box. They work extremely well. Golf glasses (with the near segment really small and low) are another alternative.

Another alternative is to wear glasses corrected for distance vision only, and use an illuminated magnifier to read charts, setting circles, and the control box. The magnifier not only magnifies the image, but also changes the focal distance so that farsighted eyes can see it.

[p. 107] Lumicon went out of business in 2002, but then was revived by Parks Optical. Giant visual backs and camera adapters for these telescopes are also available from Peterson Engineering.

[pp. 128-129] If your polar alignment is always just a bit inaccurate, see the note to p. 53 about declination setting circles.

[pp. 137-138] The LEDs along the left edge of the LX200 keypad are bright enough to be annoying, so on mine, I've placed a strip of 1/4-inch-wide white tape over them (from a tape label maker). They are still bright enough to see without difficulty.

[pp. 161-162] After the warranty on my LX200 expired, I re-engineered the power input circuitry to eliminate the floating ground and to give better reverse polarity protection, as well as eliminating the need for the external fuse. Click here for the new circuit. A side effect is that the bargraph display no longer indicates current; it serves as a power-on indicator.


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Last Revision October 7, 2009