Gavin Kohn's 3D-Printed Spectrometer Turns a DSLR and Three Lenses Into an Optical Science Tool

Maker Gavin Kohn has released a guide to turning a digital SLR camera into a spectrometer for measuring any light's spectral output, from LEDs to stars — by combining a trio of lenses and a pair of razor blades.

"This is a DIY spectrometer that can be used with DSLR lenses," Kohn explains of his creation. "This design incorporates a diffraction grating, adjustable slit, and three DSLR lenses to produce a spectrometer that can be used to measure the light spectrum from lights or even stars. It can be used as a teaching tool or a fun way to learn about light spectrums."

A spectrometer is a tool for splitting incoming light into its spectral components for measurement. It can be used on its own as a way of figuring out the makeup of a light source's emissions, or it can be used in a mass spectrometer to figure out the molecular makeup of a gas sample — while astronomers use spectrometers to work out the chemical composition of stars and planets.

Kohn's educational spectrometer is made using three different lenses, originally designed for SLR cameras. A 100-300mm zoom lens sits in front of the light source to be measured, focusing the incoming light on an adjustable slit made from two razor blades mounted in a 3D-printed housing. On the other side of the slit is a collimating lens, a 50mm prime, behind which is a low-cost plastic diffraction grating. Finally, the light passes through a 135mm lens attached to a DSLR camera — which captures the now-separated light components.

Taking measurements requires a "clean" reference sample, captured by pointing the gadget at a white LED in an otherwise dark room. Once one or more reference images are captured, the spectrometer can be trained on something more interesting — "other color LEDs, household lights, or even bright stars," Kohn suggests — and processed using a Python script to plot the light's spectra and mark its two primary peaks.

"One word of caution," Kohn notes for those looking to build their own. "I would not recommend using the Sun [as a light source] because you may damage your camera or your eyes. Remember that even with the slit, a lot of light can still get through and could potentially be a very dangerous mistake."

The full guide, including Python source code and 3D print files, is available on Instructables.