Description:

It is more complex in design than conventional 3-screw rings, and there is a weight penalty because of the secondary horizontal bar necessary for the altitude adjustment. I have found that it is just as rigid though, and the advantages far outweigh the disadvantages.

The design uses two pivots; the left-right azimuth pivot is within the front ring, consisting of 2 conical 5/16" diamter steel pins engaging in countersinks machined top and bottom in the front split-ring. The upper screw can be adjusted by hand to remove any play (though there does not seem to be any reason to touch it once set, but it's there should any wear or looseness become apparent over time). The actual azimuth adjustment is achieved using the knob on the right side of the rear main ring. The end of this screw is 1/4" diameter and has a hemispherical point which engages a short horizontal matching channel in the inner split-ring. On the left-hand side is another pin which is spring-loaded (a fairly strong spring!), and that is contained within the fitment shown in the picture, and this also fits in a matching channel machined in the left side of the split-ring. So, as you turn the knob clockwise or anti-clockwise the guidescope points left or right, with the 2 pins sliding along their channels. When the desired aligment is achieved the smaller screw on the left-hand side locks the spring-loaded pin in place. Again, this prevents any subsequent flexure.

For altitude adjustments, both main rings are fitted to a secondary bar which pivots vertically - the hinge is at the front and can be clamped by the hand knob seen at the right side of the front dovetail block. This clamp is there to prevent any movement of the hinge after the guidescope is set, though the 5/16" stainless pin running in reamed holes does not exhibit any play anyway. It's best to take no chances of flexure though. The vertical movement is adjusted using the large diameter knob just behind the rear main ring and just below the guidescope tube. I know the clearance looks tight here (it is tight!) but it's easier to adjust than you might think looking at it. The screw is captive within the rear dovetail block, and screw backlash is elminated using a hardened steel ball engaging a groove in the shank of the screw. The screw fits a pivoting 3/8" diameter steel bush fitted to the rear of the secondary bar, necessary to accomodate the changing angles as the bar moves up and down. A 1" wide extension at the rear of the secondary bar slides within a precisely machined recess in the rear dovetail block (this prevents unwanted side-side movement of the secondary bar). Turning the adjusting knob therefore jacks up the rear of the secondary bar (or lowers it) thus pointing the guidescope up or down.

To use the mount I proceed as follows:
Align the main scope on the object to be imaged or photographed. Put a low power (35 or 40 mm) eyepiece in the guidescope and look around for a suitable star to guide on. Move the guidescope a bit off-axis if there is nothing suitable quite within the FOV. Bring the star to the centre of the FOV using the adjustment procedure below and replace the eyepiece with the autoguider (after re-focussing with my parfocal eyepiece).
loosen the front hinge clamp.
Loosen slightly the rear dovetail block mounting clamp (the large black knob) - necessary because this needs to slide very slightly forwards/backwards in it's dovetail as the guidescope hinges up and down. The front one is left clamped up tight.
Loosen the azimuth spring pin lock screw on the left hand side to allow the rear of the guidescope to move side-to-side.
Turn the 2 positional adjusting knobs to bring the guidestar into center of FOV.
Tighten eveything up again.
Start guiding!

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