wpo - Gavin WPO spectrograph
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spectrographwpo - Gavin WPO spectrograph
This adaptation of the WPO spectrograph weighs a modest 12 oz [350g] without camera. It uses an old Foth 75mm fl f/3.5 3-element lens for all collimator/camera imaging plus 600 grooves/mm reflective grating and Littrow prism [below]. It couples to any Starlight Xpress CCD camera giving a focal plane dispersion scale of ~160A/mm = 1.6A per 10micron pixel.
These preliminary spectrograms of a Her, V565 Her, b Lyr [with emission lines], Arcturus and Vega via the single shot MX5c colour camera show promise - see Littrow versions below.
This
combo uses the HX5 CCD + Foth f/3.5; 75mm fl lens + Littrow prism to produce
very low resolution spectra of a similar quality to the Rainbow Optics
grating at the focal plane of a telescope but at much lower cost for the
prism.
The spectrum of daylight taken at dusk with the spectrograph plus slit [without telescope] pointing skywards covers the full spectrum from violet [~3800A] to near IR [~8500A] in a single exposure. Numerous oxygen and watervapour lines in the earth's atmosphere are superimposed onto the sun's spectrum.
Dispersion
via a prism is non-linear eg the spectrum is progressively expanded away
from the red end. Note the curvature of the spectrum [common
via prism] and slightly defocused red end - a spectrograph will detect
any residue chromatic aberration. Even the best lens will need focus
adjustment whilst traversing the spectrum unless the CCD surface is tilted
to compensate [difficult to arrange].
