wpo -  spectra - without a spectroscope!

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The CD, as a simple reflective diffraction grating, is now joined by a transmission version via the cover disk from a stack of blank CDs and useful for testing deepsky and pollution filters.
At some stage most 'discover' that by tilting a reflective grating, CD or DVD so sunlight just skims the ruled surface - the absorption lines in the spectrum are clearly visible to the unaided eye brought close to the grating surface.

Domestic fluorescent tubes [Hg = mercury], energy saving lamps and mercury and sodium street lighting will also produce a spectrum via a CD as below.

The spectrum image can be captured onto film/digital camera by replicating the eye's position with the lens focused on the target light.

*credited to Phillip Pendred-Brittany

 



Solar spectra below were taken with a digital still camera at full zoom and 600g/mm grating in 2nd order spectrum and yield a dispersion of 1A/pixel i.e. about the same as the pro-standard SBIG stellar spectrograph!  Raw images have been resampled vertically to remove artefacts.



Diffraction effects can also be seen in surfaces with regular small scale patterns like CCDs pixels to estimate the pixel size/shape in both X and Y axes.



images/text copyright - Maurice Gavin - Sept 2001/ Feb 2002/Feb 2005