Making a solar filter

With a solar eclipse coming up on 20th March 2015 I’ve finally got round to making a solar filter for my 72mm refractor. I’d looked at purchasing one but one of the right size was never in stock.  I wanted something sturdy rather than made of card and I hit upon the idea of using a CD/DVD “cake” as the main body (with a large enough hole cut in the top) and sandwiching some solar film between two rings cut from the protective discs you get at the bottom of the “cake”.  I also made a pair of filters for my binoculars out of cardboard (cereal carton).  This first image shows the body of the “cake” with a hole already cut into it, and the two protective discs. Also seen are a 12″ steel ruler, radius cutter, pair of compasses, caliper, solar film (in envelope under ruler) and “invisible” photograph mounts (which are used to attach the rings to the film)

A 15mm diameter hole (the size of the central hole in the discs) was drawn on an off-cut of fibreboard (ply would have been better) and one of the discs positioned over it and fixed in place with screws. The radius cutter was set to a radius 10mm less than that of the discs and its pinpoint located in the same hole created by the compasses

Here we see both rings completed:

Photo mounts are attached around each ring:

A square of solar film is cut just larger than the rings and, having removed the backing paper from the adhesive mounts, the film is carefully sandwiched between the rings:

The rings are then fixed in place inside the modified cake, and here’s the finished article after the main body has been painted (prior to the filter being added!):

Filter attached to telescope ready to image the eclipse:

A cropped image taken using the above: