AstroMedia: The solarscope for solar observaition

AstroMedia: The solar projector

Danger-free observation of the sun
This handy device allows several people to observe sunspots, planetary transits and eclipses at the same time, comfortably and completely safely. Thanks to a sophisticated optical system, only a projected image of the sun is visible, so no solar filter is required.

The principle
The solar projector uses the principle of the camera obscura ("pinhole camera"), which was already used to observe solar eclipses in the 11th century and is still used in every camera today: Light falls through a small aperture into a darkened chamber and creates an upside-down image of the outside world on the opposite side. Instead of a simple aperture, the solar projector has a lens and a convex mirror, which together act like a Galilean telescope and allow high magnification. A plane mirror deflects the image into a convenient viewing position.

The optics
The optics consist of a two-lens glass achromat with a diameter of 30 mm and a focal length of 250 mm, which can be stopped down to 12 mm in five steps, an interchangeable optic with 2 convex mirrors with a focal length of -10 and -14 mm and a plane mirror made of acrylic glass.

Simple operation
The solar projector is very easy to operate: It sits on a Dobsonian base and can be set to any elevation between 0° and 90°. Two integrated quadrants make it possible to determine the height of the sun. The size of the solar image is either 75 or 55 mm and can be conveniently viewed at right angles to the incident sunlight - very practical when the sun is high!

This is what you need for assembly

A firm, flat work surface. Helpful: a cutting mat (e.g. 450 x 300 mm or 600 x 450 mm)

a sharp cutter knife

a blunt knife or a folding bone

a piece of fine sandpaper

a quality all-purpose glue

a rubber ring

a thin thread

2 weights, e.g. glass beads or small metal balls

adhesive tape

for perfectionists: a black felt-tip pen