Anoher Simple CD ROM Spectroscope

Joachim Köppen Kiel/Strasbourg/Illkirch Summer 2003

Using the same arrangement as in the first experiments, we can build a spectroscope in a cardboard box with only a piece of CD and some cardboard. The layout is shown below:

1. How to cut a CD: Take a good pair of scissors, hold the CD firmly, and simply cut it from the outer rim to the centre in one go with even pressure.
2. The silvery foil of the CD is the most important part, as it contains the grooves. It may come off at the cut edges, it may come off easily when you apply glue or sticky tape to the "back" side (which contains the lettering etc). When you fix the CD piece, attach the sticky tape to the clear "front" side, into which you would look.
3. Put the CD piece on a cardboard holder which helps to keep it in a vertical position. If necessary, fine adjustments can be made by bending the cardboard sides a bit. Sometimes cardboard needs re-bending after a while.
4. Pieces of cardboard are strategically placed to serve as baffles against straylight.
5. The box should have opaque walls, and of sufficient stiffness. The interior of the box should have a dull, dark finish. Any dark cardboard will do, as long as it is not shiny. Applying black gouache (opaque watercolour) paint is most helpful.

As can be seen, there are tracings on the floor of the box which indicate the rays of light. This was helpful for placing the baffles. In this experimental version I had placed the CDROM on a small turntable which allowed to orient it in different ways. Also, for the slit I made a slider which contained slits of different widths as well as an open aperture.