Telescope Reviews: Re: Spectroscope calibration

You use a thin glass plate like a microscope slide to act like a beam splitter that is placed in the light cone from from the collimating telescope. You then use a small lens and place the scale at the focal point of the small lens and illuminate the scale from behind. The lens projects the image onto the beam splitter and the scale and spectrum are overlayed and view in the eyepiece of the spectroscope. The scale projection optics work the same way as a Telrad finder. If you use a Kellner eyepiece you can place the scale at the field stop, that will put the scale and image both at focus in the same time.
One thing to consider is the total dispersion of your spectroscope. If it is medium to high then your only going to able to view only a small section of the spectrum at one time. Your either going to have to have a moving scale, that tracks along with the tilt of the grating or do what most commerical units do, have a readout dial that shows the wavelength in the center of the eyepiece but the scale is not projected onto the eyepiece.

- Dave

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Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schief. 60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4.5" f/16 Schupmann Medial refractor, 14 Stellafane awards 7 in optics

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