Workshop on filters and spectroscopy
Saturday 10th September 2022
Paul Smith welcomed the participants and showed us the black cylindrical spectroscope that he had bought on eBay, and the free Theremino Spectrometer software running a laptop. Paul showed us the spectra from tungsten, fluorescent and LED lamps, which often included surprising amounts of infrared and ultraviolet, and from a laptop screen. He also showed us the effects of various filters that are supposed to cut UV and/or IR on the spectra, and the effects of a microscope eyepiece, polarising sunglasses and normal spectacles.
Paul Smith’s introduction to spectroscopy
Examining spectrum of ceiling lights
Spectroscope (with a white LED torch)
Theremino Spectrometer software
Pam Hamer showed us the effects of red and green fluorescent filters, which gave quite different results when the red or green filter was closer to the light source. She also showed us the spectra from white and red LED torches; the red one has a very narrow peak. Pam also showed us the effects of 4 dichroic filters that Phil Robinson had given her, and as expected they had very narrow peaks.
Alan Wood brought some Olympus microscope filters. Surprisingly, the green absorption filter and the expensive dichroic IF 550 filter (intended for phase contrast) had very similar spectra. The ND 25 neutral density filter is supposed to be neutral, but it clearly affected some colours more than others.
Alan Wood’s filters
Phil Greaves brought two Watson brass spectrometers, one hand-held and other for use with a microscope.
The microspectroscope allows the spectrum of a specimen to be compared with that of a comparison solution that was held in a tube attached to the black part. Sadly, this one gives a poor spectrum, probably because one or more of the prisms are out of alignment.
Chris Thomas attempted to record a video through the microspectroscope.
Phil Greaves and Chris Thomas
The hand-held spectroscope still works, and shows a scale alongside the spectrum. The eyepiece can be focused, and the slit aperture can be adjusted.
W. Watson & Sons hand-held spectroscope
Report and photographs by Alan Wood