DIY ASTRONOMY - Make a solar projector

How to construct a home-built projector for safely viewing the Sun

- Mark Parrish

CAUTION Never observe or image the Sun with the naked eye or any unfiltered optical instrument

This month's project is to build a solar projector, which you can use to safely view the Sun. Not only is it easy to operate, but it's useful for catching sunspot activity, a solar eclipse or a transit event. As it is not safe to look directly at the Sun with the naked eye (or any unfiltered optical equipment), our design keeps your eyes well away from the light path, which is inside an enclosed casing. The image is projected onto a screen which can be viewed by several people simultaneously.

Cost-effective design

The design makes use of binoculars, a mirror and a screen. Charity shop 7x50 binoculars are a good bet, particularly those built with metal and glass parts and costing under £10. There may be some heat build-up during observations, so don't use pricey binoculars or ones with plastic eyepiece parts. We only need to use one-half of the optics, but we can keep the other, as removing it interferes with the focus mechanism.

Before building the projector, test the optics. Take care with this; after capping one objective lens, hold the binoculars at waist height so that they point towards the Sun and project a crisp image onto a white wall or a card. We found that holding them 450mm from the wall worked well, producing a bright disc about 30mm across. You can increase or shorten the length of the viewing tube part of your projector if you need a different setup.