DIY projects - miscellaneous astro gadgets

50 mm finder (and miniscope):

	This project started off with a recycled 50mm achromatic objective lens. Looking around for a suitable tube I found that it fitted almost exactly inside a 3inch drainpipe connector (extreme left of picture) and was a good tight fit with a bit of teflon plumbing tape. The other components are a short section of 3 inch drainpipe and a plywood reducer to match the tube internal diameter to the 1.25 inches of the diagnonal.  The diagonal was a cheap 90 degree mirror diagonal from Surplusshed.
	This is the completed optical assembly. Focussing is by means of sliding the end section, with the objective lens, in and out of the tube.
	Here it is on a tripod. A tripod mounting block was made from a piece of thick ply with a part-circular cut out to match the tube radius. The small brass screw at the rear is to secure the diagonal. Et voila...an ultra portable miniscope. The objective has a focal length of about 180mm so the 16mm eyepiece shown here gives a magnification of just over 11x.

Copy scope:

	Photocopier lenses can make quite good objectives for small rich field refractors as they are often well colour corrected and have a flat field. In this picture you can see the f4.5 63mm diameter Fujinon copier lens I acquired with the original intention of making a finder from it. Unfortunately the steel lens cell turned out to be way too heavy for that, so I thought I'd make it into a compact rich field refractor. It is mounted here in a piece of MDF which will form the front of the scope.
	The focusser is a cheap plastic rack and pinion focusser (originally from a Meade refractor I think) which I shortened a lot to cope with the short light cone from this short focal length objective.
	Here you can see the main components disassembled.
	Assembled scope prior to painting and attaching a tripod bush. As you can see it is constructed from 1/4 inch ply and MDF. Apertures in the square MDF components were cut  on the lathe.

Hartmann focussing mask:

The sleeve was made from laminated cardboard (cereal box) built up to a thickness of 4 layers. PVA woodworking adhesive was used to glue the layers together. Clothes pegs were used to hold the carboard layers together whilst the glue dried. I ensured the correct diameter by building up the first layer around the dewshield of the telescope (with a plastic bag underneath to protect the scope and allow some clearance).

The front disk was made from 1/4 inch plywood, cut roughly to shape on a bandsaw and finished off  with a bench sander. The 3 apertures of 35mm diameter were cut using a forstner drill bit. The disk was attached to the sleeve with epoxy adhesive and the whole thing painted matt black to finish off.

Solar filter:

	The material I used for the solar filter was the Baader Planetarium AstroSolar safety film. This is very safe and economical material if used properly. It is sold in A4 sheets as well as larger sizes if larger full aperture filters required.
	For this project I laminated the sleeve from layers of 1/32 model makers plywood bonded with PVA wood glue. Once again the front disk was made from 1/4 inch ply but this time I shaped it on a lathe. The disk s attached to the sleeve with epoxy adhesive. The other components shown are a smaller plywood disk and a cork disk of the same dimensions used as a slightly compressible gasket to hold the Baader film in place.
	This is the finished assembly. The sheet of Baader film is seen sandwiched between the cork disk and the larger plywood disk. The components are held together with 4 M4 screws.
	Solar filter on the 120mm refractor.  With an aperture of 55mm the telscope is working at f11 giving a reasonable improvement in chromatic aberration.

Camera lens eyepiece adapter:

	I have a number of old fashioned M42 screw SLR camera lenses and it occured to me that these could be used as low power travel scopes if an appropriate eyepiece could be attached to the rear of them. I machined this adapter from a left over piece of 50mm round brass bar. The only tricky bit was getting the M42x1mm thread cut accurately but it came out OK in the end. A 1.25inch barrel eyepiece is held in place with a single knurled thumbscrew.
	Here the adapter is fitted to a f3.5 200mm lens. The eyepiece gives a nice bright (inverted) image.

Replacement focusser knobs:

	The standard knobs on the rack and pinnion focusser of my refractor looked very cheap and were also very sharp around the edges which meant getting your finger caught between the edge of the knob and the focusser was an uncomfortable experience.
	Here is the replacement knob turned from a piece of brass bar.
	The scope with the two replacement knobs; looks nicer and feels better in use.

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