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DIY Optical spectrometer / spectrograph

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2021-08-19 08:00:02

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This project was created on 10/12/2018 and last updated 7 months ago.

There are two main parts for this spectrograph: the hand-made optics and means of capturing spectra, in this case a photo camera. Also there is little addon for calibrating by wavelength -- the neon glow lamp.

The optics is just a box lined with black cardboard, and several apertures inside, made of the same black cardboard. The apertures are made for reducing stray light. Entrance slit is made from two blades used for retractable knife. The dispersive element is 600 lines/mm Chinese transmission diffraction grating on PET substrate. There is no collimating optics inside, so light incoming on the grating is slightly divergent, angle of divergence is ~5 degrees from center line. This is probably the cause of slight distortion of the spectrum. In the end, this geometric distortion is readily dealt with software.

The camera I use is modified Canon A490, bought second-hand for just about 10 USD. The modification - removing the IR-blocking filter - was made by me after buying it. The camera is loaded with CHDK "alternative firmware" which allows to shoot raw and have total manual control. Also through the use of related software chdkptp one can remotely control the camera from PC. 

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