This project will show you how to build a solar projector that you can use to safely view the Sun.
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 that can be viewed by several people simultaneously, making it a good option for astronomy outreach at star parties.
For more on solar observing, read our guide on how to safely observe the Sun.
The design makes use of binoculars, a mirror and a screen.
Charity shop 7×50 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.
To reflect the light up towards the screen we glued a small, cheap mirror onto an adjustable platform.
We found this spring-loaded platform invaluable when finely adjusting the projector, so the image could be seen centrally on the screen.
The screen itself is made from a piece of glass. We applied a layer of matt white spray paint to the back and found it captured the image well.
Once the projector is built it needs to be directed towards the Sun and held steady for viewing.
We made a table-top fork mount for this. The unit pivots vertically between the forks and the whole thing can be rotated on a flat surface.
We added a front panel to our projector to block off the unused half of the binoculars.
The panel also reduces the aperture to about 25mm diameter as we felt the image was too bright; this also helps to stop heat building up inside.
We extended this panel above the top of the front section and drilled a small hole in it.
This casts a shadow, with a bright spot caused by the hole, onto the outside of the viewing tube, which helps when aligning with the Sun.
Tools and materials
- Marking-out tools (ruler, square and pencil)
- Coping saw
- Drill and bits
- Glass-cutting tool
- Approximately 1,800mm-length of softwood
- 80mm x 12mm or similar
- Medium sheet of 3mm plywood
- Thick plywood or similar for base
- 150mm of M6 studding
- 3 x small springs – approximately 6mm in diameter x 25mm in length
- 3 x M4 x 40mm CSK screws
- 2 x M6 x 40mm CSK screws
- M6 and M4 nuts and washers
- Small round head woodscrews
- Binoculars, 7x50s or similar, with heavy metal/glass construction
- Small, flat, pocket-sized mirror
- Matt black and matt white spray paint
- Wood glue
Build a solar projector: step-by-step
- Mark out the wooden parts
- Cut walls and mount parts from softwood and panels from thin plywood
- Make sure all the edges are sanded smooth
- A coping saw can be used to make the curved lens supports, but we drilled large holes and cut across
- Glue the walls and the lens supports to one of the outer panels (the other panel is put on later)
- Glue on two fixed dividers behind the body of the binoculars
- Use M6 studding, a loose wooden divider, a metal bracket and nuts to clamp in the binoculars
- Use plywood to make a mirror mount; M4 screws are glued into this, and pass through holes in the 45° wall (with springs between and wingnuts, for adjustment)
- The mirror’s centre should align with the lower eyepiece and reflect light up to the screen
- Remove the binoculars and mirror, and paint the insides matt black; we also painted the outside white.
- Cut a piece of glass for the screen and spray one side matt white.
- This fits into a slot in each wall near the top of the viewing tube. Reassemble when dry.
- With one side panel removed so you can adjust the focus, carefully test your solar projector by leaning it back to align with the Sun
- It is essential that you make sure the upper lens is capped when you do this, and be very careful not to look into the eyepiece
- Once you are happy with the test, you can screw on the second panel
- Balance the projector on a corner, and draw a vertical line up the panel from it, then repeat for one or two more corners
- Where the lines cross, drill a hole in each panel and use M6 screws to make the pivots
- Make a simple fork stand to suit the finished size
This article originally appeared in the April 2022 issue of BBC Sky at Night Magazine.