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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