==== Components ====

A. Opening to optical box
B. Entrance slit made of razor blades
C. Baffles to reduce scattering
D. Achromat focused on slit (old binocular objective works fine)
E. 1-inch square reflection grating (Edmund Scientific - about $10)
F. Achromat focused on eyepiece (another binocular objective)
G. Eyepiece (an old 25mm Kellner works fine)
H. Spring tuning device and turn knob

==== How I built it ====

I mounted all the optical components onto little wooden squares like chessmen and arranged them on a large piece of cardboard in the "V" shaped light path shown. I directed a light beam from a slide projector into the slit, then adjusted the optical components until they produced a spectrum. The final size of the instrument depends upon the focal length of the achromats used. When the layout was just right I traced the positions of all components onto the cardboard, which became the floor plan for the optical box. The grating is mounted on a rotating base which can be moved back and forth to tune the instrument. Finally, I built a wooden box around the whole thing, painted the interior a flat black and mounted it on a simple tripod. Later I added a filter wheel ( yellow, red and neutral density) in front of the slit to improve the contrast in various spectral regions. I am pleased that this low-cost instrument is capable of showing many hundreds of absorption lines in the solar spectrum.