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Baader Planetarium Spectroscope

Posted by Glen Ward   10/22/2007 12:00AM

This is a review of the Baader Planetarium Grating Spectroscope. I cannot make the picture upload work with my computer, but I would be happy to send pictures to anyone who requests them through Email.

I have been involved in astronomy for about twenty-five years and during that time I have often been interested in obtaining a spectroscope. When I first started in astronomy, about the only thing available was a prism spectroscope which was very expensive. Today, there are at least three choices for less than $300 - The Rainbow Optics Star Spectroscope, the Rigel Systems Spectroscope, and the Baader Planetarium Spectroscope.

I chose the Baader Spectroscope because I liked the features it includes. The Baader grating is rated to put 82% of the light into the first order spectrum. In addition, the body of the spectroscope is designed both to hold an eyepiece for visual use and with a T-thread for photography. Having a separate body to hold the eyepiece eliminates handling of the fragile grating in the dark. Also, it is made similar to an eyepiece projection adapter in that it extends to vary the distance from the grating to the film or CCD.

The unit comes in a small, clear plastic box. The box is barely adequate and could be better. I will probably replace it with a small eyepiece case. The instructions proved to be a disappointment. They are rather unclear and throw unneeded technical information at us while failing to explain the basic lines in the spectrum. Still, the spectroscope is easy to use and explanations of the lines can be found onlne, so the instructions are hardly needed. In fact, I found myself referencing online instructions for both the Rainbow Optics and Rigel Systems spectroscopes in order to learn more about what I was seeing.

The parts of the spectroscope are very well made. The main body is made from metal and includes caps for both ends. The grating screws into the main body and has its own storage box. Also, there is a lens which is placed over the top of the eyepiece to spread the spectrum to make the lines visible. Unfortunately, I found that this lens would not fit most modern eyepieces which have rubber eyecups. It will work with older Orthoscopics, however.

In practice, the spectroscope is very easy to use. One simply places an eyepiece in the unit and puts the spectroscope into the telescope's focuser. Without the spreading lens in place on top of the eyepiece, the direct image as well as the bright first order spectrum can be seen. It is a simple matter to center up the first order spectrum of the desired object, which appears as a narrow rainbow line. Then the spreading lens is placed on top of the eyepiece, the lens is rotated to spread the spectrum, and fine focus is made to bring out the lines.

On bright stars like Vega or Sirius, the spectrum is surprisingly vivid and quite beautiful. The spectrum shows the main hydrogen lines easily and other minor lines pop in and out of view depending upon the seeing. Unfortunately, the seeing from my site in West Virginia is usually very poor and the spectroscope can be a little frustrating to use under these conditions.

Although it is possible to use the spectroscope on extended objects like planetary nebulae and galaxies, I have found this to be rather difficult owing to the dimness of the objects in question.

One problem I encountered is that the complete spectroscope requires a lot in in-travel in the focuser. My 8" Meade Starfinder lacked enough travel to bring the spectroscope to focus. However, it turns out you can just screw the grating into the eyepiece like a filter and forget about the spectroscope body, solving the focus problem. This does undo one of the great advantages of the Baader design over the competition - when using the spectroscope body, it is not necessary to handle the fragile grating when changing eyepieces. Other telescopes I have used the spectroscope with include a Hardin 10" Newtonian and a C-102 refractor.

Another problem I have found is that the spreading lens does not seem to spread the spectrum very much with higher magnifications. In addition, the assymetric rubber eyeshade on the spreading lens is useless because the lens must be rotated to adjust for maximum spectrum width. I removed it.

I have not tried imaging with the spectroscope but I expect that it would work quite well. As mentioned before, the length of the main body of the spectroscope, and thus the length of the spectrum on the film, is variable to accomodate imaging work.

Overall, I like the Baader Planetarium Spectroscope. The instructions could be better and the unit is a little cumbersome to use. Still, it does what it is suppposed to do and provides an interesting new angle for one's observing.