Eyepiece Support
A block of hardwood (maple preferred) 3" square and 1" thick should then be taken to a pattern maker and shaped to fit the curve of the tube, and also to have a 1⅝" hole bored squarely through its center. This block is fastened over the opening in the side of the tube as shown in Fig. 58.
At the same time have another block of similar dimensions (except see second
paragraph below) bored out to receive a brass bushing having an inside diameter of 1 5/16". This bushing should be about 1½" long, with a wall thickness of either 1/16" or 1/8", and must fit tightly into the block. It should be sealed in with shellac. It will be much better if the bushing has a flange at one end. The eyepiece adapter tube, which should telescope snugly and smoothly into the bushing, is a piece of brass tubing about 4" long, II/4" inside diameter, with a 1/32" wall.
One end should have three or four longitudinal slots cut into it for a length of about 1"; this can he done with a thin-bladed hack saw. The walls can then be sprung in with slight finger pressure, insuring a firm grip on various eyepieces. Quite often, the adapter tube fits too tightly in the bushing, and some filing and abrading with emery paper must be resorted to in order to effect a smooth fit. A machinist
can do this job quickly on a lathe, holding the tubing on a mandrel.
The two wooden blocks are joined as shown in Fig 58, with three compression springs between the matched angles to provide an adjustment that will bring the deflected axis of the mirror and the axis of the adapter tube coincident.
If the tube is accurately round, as, for example, a seamless aluminum tube, it will be possible to dispense with the spring adjustments described. In this case only a single block of wood at least 1¼" thick is used. One surface is milled to fit the curve
of the tube, and a center hole, of a size to accommodate the bushing, is bored radially to this curve, automatically bringing the adapter square to the tube.
Even if the adjustment is not quite accurately made mechanically, it can be corrected by inserting shims where needed between the block and the tube. Another advantage of this arrangement is that it makes possible placing the diagonal about %" closer to the focus; as this would alter many of the foregoing
dimensions, plan the change carefully if you decide to make it.
Next- Diagonal Holder
|
|
