The 3 Inch Refractor

This telescope started out from the desire to have a small telescope with more magnifying power than a spotter scope. Looking about on Trademe at various small scopes I came across a bargain priced refractor objective, so I plunked down my cash and waited.

What arrived was a beautiful 3 inch F/15 objective in a brass cell, made by the now defunt British firm of Broadhurst and Clarkson. There's a minor chip in the edge of the crown element, but otherwise it's in immaculate condition. Apparently the complete telescope that this was for was purchased in the 1950s, but the objective was removed and replaced with a different one. Eventually over time, this telescope was lost but the objective remained.

 

 

The focuser-drawtube is a plain piece of brass tube that rests on a tray made from heavy brass angle. The three brass bolts are used to line up the focussing mechanism with the centre axis of the telescope. A pressure plate (Not seen here.) pushes down on top of the drawtube, pressing it agains the tray. The last picture shows the small nut forced into the PVC bushing for the eyepiece locking bolt to screw into

The telescope tube is made from heavy walled PVC tube with wooden reinforcing rings. these also act as light baffles. The tube was painted a plain gloss white, but I had considerable trouble getting a good coat brushed on, so next time I do this I'm going to get a spray can

The next step was to make the tripod. One of the main requirements was that this telescope had to be transportable by car, so to that end the legs had to be collapsable. As you can see the upper part of the leg sandwiches the lower. But rather try and make this a sliding extending leg, I just to just drill holes so there was a extended and retracted position. The first picture shows the legs being coated with Danish Oil, a wonderful turps based varnish that sinks straight into the wood grain. The pinewood ended up with a beautiful honey coloured lustre.

Shiny steel parts being spray painted with gloss black enamel

The assembled tripod. The tripod head is a triple layer of 18mm ply glued together. through the middle a hole was bored and a length of 15mm brass nipple was screwed in for the telescope cradle.

And finally the completed telescope. The telescope uses Dobson style bearings. The azimuth bearing is a long bolt that goes thru the brass nipple. Heavy nylon washers are used.

A series of pictures taken through and of, the telescope.