this is something I have been meaning to do for
some time. It is a poster showing the spectrum of the Crab plus images taken
through four different line filters, [SII], Halpha, [NII] and [OIII]. Finally
it shows three tricolor images made by using various combinations of
filters.
Have a look if interested
note how one of the images is comprised of three
emission lines all found in the red visible spectrum ([SII], [NII], Halpha).
Another shows an image made from only Halpha and [NII] demonstrating that the
two lines, separated by only 2nm, are indeed separated by the filters.
The images were taken in late 2003 using a C14,
Custom Scientific 3nm narrowband filters, and an FLI Dream Machine. Exposures
were all 45 minutes and three were taken per emission line
filter.