SJAA Ephemeris April 2000 | SJAA Home | Contents | Previous | Next

Loaner Program to Include Spectrograph

The SJAA loaner program will soon add a Rainbow optics Star Spectroscope to its arsenal of startools.

This nifty little gadget is easy and fun to use. The star spectroscope itself consists of two nicely machined parts: a blazed diffraction grating in a protective cell that spreads starlight into a spectrum of colors, and a lens cell that contains optics to widen that spectrum and make the dark absorption lines easier to see. The grating cell screws into the end of an 1.25 inch eyepiece just like a filter. (A medium power eyepiece generally works best, depending on the focal ratio of your scope.) The lens cell fits over the top of the eyepiece and is held in place by three nylon thumbscrews.

Using the spectroscope is easy. Simply screw in the diffraction grating and adjust the focus until the spectrum is as narrow as possible. Then slip the lens cell over the eyepiece and turn it to widen the band of colors. Refocus slightly to bring the absorption lines into sharp focus. It's that simple, although you may want to tinker around a bit to optimize your setup. (Complete instructions are included in the owner's manual.)

The spectroscope is slitless and thus does not work on extended objects such as nebulae. But it is helpful in identifying stellar planetaries and has been successfully used for CCD imaging.

You'll need to contact Mike Koop, the SJAA Loaner Program director ( for information about loans of the club star spectrograph.

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Last updated: July 19, 2007

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