DOVETAIL ACCESSORY BARS - BASIC KIT
9th July 1999: Illustrations of Current Design Revision for LX200 Dovetail Bar Sets.
 Revised design of Dovetail Bar Set (this example, 12" LX200). Note there are two accessory tubes incorporated into the lower pair of brackets, the trimming weight may be used at either end of each tube. Whilst not shown, also included are 12 stainless steel mounting screws. |
 The underside of the front end of both dovetail bars are machined out to give neutral balance with no equipment loaded. The new bracket design allows the two dovetail bars to be positioned exactly on the OTA centerline providing even weight distribution around the RA axis. |
 The new bracket designs. 12" at rear, 10" middle and 8" at front, the lower brackets are on the left and the upper brackets on the right. The brackets are machined from 1" thick alloy plate and anodised black (both raw machined and anodised finshes shown here). |
 Close-up of an 8" LX200 lower bracket. |
 The camera bracket. |
 Selection of weights, clockwise from upper-left: 5lb 2-D weight, 2lb 2-D weight, 3-1/2lb bias weight, 3-1/2lb trimming weight. Apart from the 5lb 2-D weight the remainder are standard and included in the kit. |
| There have been very modest price increases due to the extra work and materials necessary for these design improvements. Even so, the entire kit is still available for less than half the price of a premium eyepiece! These new prices are shown in the pricelist. |
General Description:
The main purpose of these bars is to provide rigid support for mounting relatively heavy accessories such as guide scopes and piggy-back cameras. The most important feature is that the bars should be rigid - in particular, they need to be able to resist flexure due to changes in weight distribution as the telescope slews to different parts of the sky. This is most important where auxilliary telescopes are being used to guide the main telescope for long exposure photography. Should the bar (or mounting rings) flex even very slightly the image in the guide scope will shift relative to that through the main scope causing star trailing on the final photograph.
My accessory bars are milled from solid aluminium barstock and then black anodised. A logitudinal channel is machined on the underside to bias the weight distribution towards the rear of the OTA minimising the total weight required to achieve balance. The curved mounting seats are accurately machined to match the radius of the optical tube so that there is no stress applied when bolted up tight, their footprint is large (spanning 3 mounting screws each) to provide the utmost stability and accuracy of alignment. The standard cross-section of the dovetail bar is 1-1/2" x 1/2" with a 1" x 1/4" dovetail. This cross-section is sufficient to support any reasonable weight of accessory likely to be mounted on the telescope without flexing (at least 10lbs applied to the center of the bar). Whilst a larger cross-section (1-1/2" x 5/8", with the same 1" x 1/4" machined dovetail dimensions) can be supplied for 10" and larger telescopes, you should consider whether the standard LX200 mount (particularly when using a wedge) is going to be stable enough to carry the additional load of such heavy accessories (not to mention the added weight of the thicker bar). You may well find that the instability caused by the additional weight when applied to the telescope mounting negates any potential gains in stability due to the thicker cross-section. However, if your OTA is mounted on a seperate heavy-duty mount (perhaps a German Equatorial mount) the larger cross-section bar may be of some value. If you are going to push the mount to the limit with heavy accessories then I suggest you seriously consider replacing the nylon DEC bearings with roller bearings.
It's crucial that the combined accessory mounting hardware and instrument package (guide-scope, camera etc.,) be accurately balanced, and my integrated balance/mounting kit makes this task particularly easy. Accurate balance is important for the Meade LX fork mount to avoid undue stress on the DEC and RA motors (and Celestron SCTs have to be even more accurately balanced otherwise the motors will simply slip or stall). What is required is 'dynamic' balancing - i.e., the weight be distributed evenly about both the RA and DEC axes so balance is maintained during tracking for any pointing position. A good example might be a fairly large 90mm refractor guide scope (such as my own - see pics). This OTA is quite long (1000mm FL) with the weight some 8" off-axis above the main OTA, a tricky load to balance correctly. Ideally, the balance weight placed beneath the main OTA should be a mirror image of the weight distribution of the guide scope, and this can be approximated with the combination of Bias and Trimming weights supplied.
Counter-balancing is such an important issue that the dovetail bars I supply (and use of course) were specifically designed with an integrated balancing system. Using this system, any realistic load of 35mm camera + guide-scope + guider/CCDcamera can balanced accurately. Your LX200 will thank you for correct balancing by not burning out motors, tracking more accurately, and also quieter operation - nothing sounds quite so sad as an LX200 groaning under the strain of slewing whilst out of balance!
With the pair of dovetail bars supplied in the basic accessory/balance kit you can firmly mount virtually anything (sensible that is...) onto your LX200 *and* get it in balance. The standard dovetail and accessory mounting blocks provide for the most flexible mounting arrangement possible. Example loads are guidescope (mounted using my standard rings), large telephoto lenses with the camera body mounted on the camera platform (with special support plates and/or rings if necessary), Video cameras for afocal projection (using an extension bracket), special brackets for piggy-back CCD camera mounting (try this using 35mm camera lenses for extremely fast wide-angle shots!), and I can even supply standard alloy blocks machined to fit the dovetail - complete with locking knob - so you can adapt them for your own special uses!
Detailed fitting instructions can be found on this page should you need them (fitting is quite straightforward).
Please see the page on Counter-Balance Weight system for further details.
In the pricelist please note I now ONLY quote prices for the supply of paired dovetail bars which include the integrated balance weight system for reasons stated above.
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Revised design of Dovetail Bar Set (this example, 12" LX200). Note there are two accessory tubes incorporated into the lower pair of brackets, the trimming weight may be used at either end of each tube. Whilst not shown, also included are 12 stainless steel mounting screws.
The underside of the front end of both dovetail bars are machined out to give neutral balance with no equipment loaded. The new bracket design allows the two dovetail bars to be positioned exactly on the OTA centerline providing even weight distribution around the RA axis. 
The new bracket designs. 12" at rear, 10" middle and 8" at front, the lower brackets are on the left and the upper brackets on the right. The brackets are machined from 1" thick alloy plate and anodised black (both raw machined and anodised finshes shown here).
Close-up of an 8" LX200 lower bracket. 
The camera bracket.
Selection of weights, clockwise from upper-left: 5lb 2-D weight, 2lb 2-D weight, 3-1/2lb bias weight, 3-1/2lb trimming weight. Apart from the 5lb 2-D weight the remainder are standard and included in the kit.