Rigel RS Spectroscope

[chiltonstar]

Seeing the Rigel RS system advertised in Astronomy Now this month, I looked on their website to see if it offered inreased resolution compared with other non-slit systems, particularly as it is advertised as a "medium resolution" system.

The example spectra shown don't appear to be any better than with the Star Analyzer, despite the much higher price tag.

Have I missed something?

Chris

[robin_astro]

Hi Chris,

The RS design has been round a long time and is quite interesting as it is a classical fully collimated design using the eyepiece as the collimator and the camera lens to focus the image. It has the potential to give somewhat high resolution as the grating is not in the converging beam as in way the Star Analyser is normally used but I dont know to what extent this is achieved in practise (I dont think I would describe it as "medium resolution") and as you say is rather costly for what it is (The grating plus an angled holder to fit over the eyepiece) If you are interested you can build the SA200 into a similar sort of arrangement, as here on my website for example. 

http://www.threehillsobservatory.co.uk/astro/spectroscopy_19.htm

(You can even use an SA100 in this configuration but the lenses need to be longer focal length with the SA100 to make it worthwhile)

Cheers

Robin

[rigelsys]

Visually (it is equipped to be used visually) the RS spectroscope will show spectral lines in O,B,A,F,G,K and M stars.  The lower dispersion gratings (e.g., 100 lpmm) will typically only show spectral lines in A and M stars visually.  And you'll note they're not advertised as being used visually, only with an imager.  The spectra shown on the website were shot straight with a Canon DSLR in color, and resolution is limited by the size of the star image (it's a slitless spectrograph) and what the DSLR is capable of (note lines are weak where the 3 RGB filters cross on the camera) and are jped to medium resolution.  Using a monochrome CCD with a camear lens will produce sharper resolution, but then one has to fake in the colors (i.e., have the software colorize the spectra -- something like colorizing B&W movies). Note also, spectra are noisy, and unwidened spectra will have artifical (noise) spectral lines introduced that look sharp, but aren't spectral lines.  And one can stack the spectra (as shown on the website for the ring nebula) to increase resolution and reveal low contrast spectral lines.

So all else being equal the RS spectroscope 600 lpmm will produce higher resolution than 100 and 200 lpmm gratings.  It's all in how one uses it.