LX200 - Optical Tube Assembly Balancing System

These bias weights are fitted below the OTA to achieve crude balance (OTA remains front heavy)
Two bias weights fitted to the tube on my scope, to counter balance most of the weight of my 90mm refractor guide-scope
The fine-balance trimming weight.
The 2-D bracket and weight.
The addition of movable weights on the left-hand side of the fork help to balance in R.A. without further loading the OTA.
Note: the description of the counterweight balancing system used here forms part of the Dovetail Bar assembly for mounting accessories on the LX200 OTA. I offer this balancing system for sale together with a pair of dovetail bars, it is not available seperately as it's mounting is integral with the dovetail bar seats.
Counter-balancing is critically important for the correct operation of any astronomical telescope, and this was never more true than in the case of the wedge mounted LX200 (or LX10/50) when carrying heavy accessories. Failure to balance the OTA correctly with a heavy payload will result in poor tracking performance at best, and a higher probability of rapidly worn drive-trains and burned-out motors.

When I starting adding accessories to my own 10" LX200 it quickly became apparent that good counter-balancing was not particularly easy to achieve. One can add weight in one position to achieve a static balance, only to find that the scope is then out of balance when pointed in a different direction. The trick of course, is to achieve dynamic balance - such that the OTA is in correct balance wherever it's pointed. To do this means the center of gravity of the OTA needs to coincide with the center of the optical axis, in the middle of the DEC bearings, and in line with the RA axis. Further, when exchanging payloads it's necessary to re-adjust the weight distribution quickly and easily so that this balance is maintained. It is simply not possible to do this with a single-point weight placement.

In designing this system first off I had to decide what were the most likely combinations of payload I would carry on the optical tube assembly, and then how much weight would need to be added - and also where to put it. My own common payload items are:

The balance weight system I constructed was split into 3 components: In use, the bias weights account for the bulk of the couterweight requirement (I use 2 for my refractor), placed to the rear and below the OTA they are set to almost balance a guide-scope mounted on the top dovetail bar. One of the bias weights is removed if I also have a 35mm camera mounted on the lower dovetail bar. To bring the OTA into exact balance the trimming weight(s) adds leverage to the bias weight, and by virtue of sliding it forwards and backwards balance can be corrected for heavy or light eyepieces. The 2-D weight set can be positioned above or below the OTA when the guide-scope is not in use, I don't need use it often but it is provided for maximum flexibility of accessory mounting options.

The RA weight shown in the photo above is there to bias the fork balance towards an anti-clockwise direction. The advantage of this is that the RA worm is held in close contact with the RA gear, and tracking is thereby improved. I don't supply this weight as it requires drilling the left fork arm, but you can approximate it's effect by taping (or otherwise fixing) a weight in the same position.

A complete set of weights (Bias, trimming and 2-D) is supplied with the twin dovetail bar mounting system for 8", 10" and 12" LX OTAs.

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