Fitting a dovetail bar to a Stella Mira 66 ED APO refractor

The Stella Mira 66 ED APO doublet refractor is a serious and high quality telescope with very good colour correction. However, it doesn't have mounting rings and instead has a ridiculous mounting shoe that could be used to attach it to a photographic tripod or maybe a tracking mount; but when it comes to mounting the scope on an astronomical mount such as the Celestron AVX, the shoe is outside of all concepts of good design. It can fit into the dovetail slot and be held by just one of the two holding bolts. A result of this is that it is virtually impossible to mount the scope parallel to the polar axis as the single screw pushes the back of the shoe to the east side of the slot, pushing the front of the shoe towards the west side of the slot. Moreover, this process also tends to push the back of the mounting shoe down and slightly raise the front of the shoe. The result is a scope that is not pointing true in either axis when in the home position. Also the scope feels very precarious.

There is a Stella Mira vixen style dovetail bar to which the scope is assumed can be attached. However this is not so. The shoe cannot be mounted directly onto the dovetail bar and provide a better balance for the scope because the dovetail bar will collide with the huge focus locking device. This means that spacers have to be improvised as there are none provided for the purpose. Even though the dovetail bar is actually printed with the Stella Mira name, it is just some sort of generic bar with a slot through which attaching 1/4" UNC photographic thread bolts can pass, but is far too wide and so allows the bar to be moved from side to side even when completely tightened down.

In order to solve all of these problems I enlisted the help of a couple of packing spacers, epoxy resin and some black Sugru mouldable glue.

A year ago in another article, I described the fitting of a ZWO AEF focuser to the scope.

The bracket for the focuser had to be modified but not the scope and the fitting of the AEF in no way exacerbated the problem of fitting a dovetail bar.

A thick packing spacer was attached by Epoxy resin to the base of the mounting shoe

A thinner spacer was then attache by Epoxy resin to the first spacer to provide the desired clearance

The packing spacers provided the required clearance from the focus locking device on the right hand side. Of course this does not have to be tightened as the rack and pinion focuser is held firmly by the AEF

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Two 1/4" UNC photographic thread 1" length hex socket head bolts were used to attach the dovetail bar to the shoe and Epoxy resin was also used between the dovetail bar and the packing spacers.

Black Sugru mouldable glue was used to pack around the screws and between the two rails of the dovetail bar. After a couple of days the Sugru has become hard so that no lateral or twisting motion is possible

The completed modification

The Stella Mira mounted on the AVX mount much further forward than was previously possible providing much improved balance with true and rigid positioning.

The scope can now function the way that we require for our work.

The modified scope in action