Workshop on filters and spectroscopy

Saturday 10th September 2022

blue-link-icon-18 Quekett members can watch a video of this workshop.

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 spectroscopyPaul Smith’s introduction to spectroscopy

Examining spectrum of ceiling lightsExamining spectrum of ceiling lights

SpectroscopeSpectroscope (with a white LED torch)

Theremino Spectrometer softwareTheremino 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.

Pam HamerPam Hamer

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 filtersAlan 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.

Watson spectroscopeWatson microspectroscope

Chris Thomas attempted to record a video through the microspectroscope.

Phil Greaves and Chris ThomasPhil 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 spectroscopeW. Watson & Sons hand-held spectroscope

Report and photographs by Alan Wood

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