LX200 Telescope


I sold this telescope in 1997. This description remains since most of my photos were taken with this setup.

I have an 8" Meade LX200 Schmidt Cassegrain f/10 telescope. It is one of the early LX200's and works extremely well. I never chose to upgrade the version 2.4 ROMS and so don't have the HP pointing or 2-star alignment. Also, it has only 740 objects in its database, some of which have wrong coordinates. Most notable is an error in the coordinates of Polaris which necessitates a slightly altered polar alignment procedure. These limitations are minor and are easily circumvented by taking advantage of the GOTO feature.

The optics give good diffraction patterns and produce pin-point stars over most of the field. The fork mount is sturdy enough for astrophotography, and the electronics are extraordinary. The GOTO feature makes it possible to observe objects at the threshold of visibility because there is no uncertainty in the object's location. I chose the 8" despite the small aperture and am glad I did. The 10" LX200 is considerably larger and heavier.

Altazimuth Mode

The scope is often used in altazimuth mode for observing. The 1-star alignment procedure I use requires that the scope be level and that the longitude and latitude be known. Also, the time must be accurate within a few seconds. I have to reset the clock every few months.

The bubble level mounted on the LX200 is not sufficient for proper leveling, and a 2 inch line level is used instead. The line level is placed on the base next to the RA lock, and two of the tripod legs are adjusted. The tube is rotated 90 degrees and the remaining tripod leg adjusted. The procedure is repeated until level. The scope is then aligned using the standard 1-star alignment procedure. The accuracy of this method is sufficient to place objects within the central region of a 26 mm eyepiece. The major advantages of the altazimuth mode are the ease of alignment and the fact that the eyepiece is never at an awkward angle. Also, the scope is very stable in altazimuth mode, and vibrations dampen out in less than 1 second.

Polar Mode

For astrophotography, the scope is used in polar mode with a wedge. The scope is roughly leveled and then aligned using Meade's standard polar alignment method. In this procedure, the scope slews to the RA and DEC of Polaris, which is centered by adjusting the wedge. The scope then slews to a bright star close to the celestial equator and centered using the hand controller. Since there is an error in the coordinates of Polaris for version 2.4 ROMS, the procedure is performed manually using the GOTO and SYNCH commands. The procedure is repeated until convergence is obtained with a 9 mm eyepiece. Typically, about 15 minutes are needed for good polar alignment. The pointing accuracy is slightly better than in the altazimuth mode, and objects are routinely placed in the center of a 12 mm eyepiece.

Although polar alignment is required only for astrophotography, I sometimes use the polar mode just for observing. This is because the eyepiece is always on the same side of the telescope, and an observing table can be conveniently placed nearby. However, the scope is not as stable as in the altazimuth mode, and vibrations dampen out in about 2 seconds.

Telescope Balance

To make autoguiding easier during astrophotography, the telescope should be balanced. The declination motor of the LX200 is housed in one of the fork arms, making one side of the telescope heavier than the other. If the RA lock is released while on the wedge, the scope will rotate clockwise about RA due to the extra weight in the right fork arm. To balance the scope in RA, I filled a ziplock baggie with BB's and placed it under the DEC circle of the left fork arm.

The Taurus camera system I use is very light, and no counterweights are needed for manual guiding. However, the CCD head of the ST-4 autoguider is quite heavy, and proper balance requires a counterweight. I use an old palm-sized TV whose weight just happens to approximate that of the ST-4. The wrist strap of the TV is attached to a piggy-back adapter that is mounted on the front underside of the optical tube. This is a temporary arrangement until I purchase a real counterweight system, but it seems to work.

Maintenance

Schmidt Cassegrain telescopes can exhibit image shift problems during focusing. To minimize this effect, I occasionally rack the focus all the way in, then all the way out while the OTA is pointing straight up. This redistributes the lubricant along the baffles allowing the mirror to slide more easily in its assembly.

Meade's wedge is often criticized for being difficult to adjust. With time, I noticed that the azimuth control became very hard to turn while the scope was attached, making fine adjustments almost impossible. Upon close examination, wear was apparent along the edge of both the wedge and tripod head that supports most of the weight of the telescope. Apparently, this worn region was binding. The application of a small amount of ArmorAll along this edge made the azimuth control operate more smoothly, but this was only a temporary fix. A better solution is to attach the wedge to the tripod with 3 hex bolts (including washers and lock washers) and insert 3 nylon washers between the wedge and tripod. The hex bolts are kept loose, and the spreader bolt is used to tighten the wedge on the tripod as usual. An additional advantage to this arrangement is that the wedge can be left attached to the tripod with the 3 hex bolts, even when the legs are folded.

I cleaned the outside of the corrector plate once after I noticed an apparent film. The procedure I used was as follows. Cotton balls were wetted with a 30% solution of pure (laboratory grade) isopropyl alcohol in deionized water containing a few drops of Dawn Free liquid dishwashing detergent. (Dawn Free contains no perfumes or softeners.) The cotton was very lightly wiped over a small area of the surface. A new cotton ball was used for each section. A cotton ball wetted with only deionized water was used to remove any residual alcohol. If water streaks formed, a nonperfumed Kleenex was lightly touched to the surface of the corrector plate to wick away the water.


For more information on the LX200 telescope, see the Meade Advanced Product Users Group archive (where did it go?)

Me and my son at the 1996 Winter Star Party. I am the one on the right.

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