Jack Schmidling Productions, Inc.
18016 Church Road ~ Marengo IL 60152
Phone:815 923 0031 ~ Fax:815 923 0032 ~ Email:arf@mc.net

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There are many commercial diagonal holders on the market at very modest prices so there seems little incentive to make this part of a telescope. That is until one spends enough time struggling with the standard style that has four screws fighting against each other. Getting these things pointed the right way can be more luck than design.

The holder described here was made in a few hours and is the only one I have ever used that actually feels like it is doing what I tell it to do. Although I have a machine shop for such projects, this could be made with nothing more ellaborate than a drill press and hack saw.


The key to easy adjustment is the single central spring and three adjustment screws. Any screw can be adjusted without considering either of the others.

The actual mirror holder is cut from a piece of aluminum bar stock of any convenient size that is smaller than the minor axis of the mirror. The one shown is for a one inch diagonal and this is about the lower limit in size. It is cut on a 45 degree angle and the mirror is glued with RTV directly to this face. The other face has three tapped holes to receive the adjustment screws and a shallow hole to keep the central spring from moving about.

The mounting stud fits into conventional spiders in the usual manner and the other end is screwed into a hole in the center of the adjustment disk.


The end of the stud protrudes through the disk far enough to provide a seat for the spring which is just slightly larger than the screw. The holes for the screws are clearance holes large enough to provide easy movement of the screws. I used socket head screws to accommodate an Allan wrench for adjustment. The tapped holes in the mirror holder must be deep enough to provide sufficient lattitude for adjustment.

If you have studied my mirror cell design [Mirror Cell] you will note a striking resemblance. I pondered this one for quite awhile before realizing that if I just put the tapped holes in the disk instead of outside with wing nuts, it would work as well as the mirror cell. Being much smaller, a single spring serves the purpose. For dew prevention, I milled a narrow slot in the long side of the mirror holder and epoxied a 500 ohm, 1/4 watt, resistor in place and snaked the wires out along the spider vanes.

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