Crab: Exploring the Red Spectrum in detail

I took an image of M1 last night that I think is very interesting.

I used emission line filters that have passbands all within the "Red"
portion of the visibile spectrum.

The filters, [SII], [NII] and Ha, vary from 673nm to 656nm. The [NII] and
the Ha are very close together, separated by 2nm only (656.3 vs 658.3nm).

Since these three emission lines are all in the Red portion of the spectrum,
when the Crab is imaged with RGB, you don't see much differentiation among
the [SII], [NII] and Ha regions in the nebula.

But using a filter for each, a tricolor image can be created from data that
orginated completely within the "Red" part of the spectrum.

Such a false color representation helps to provide visualization of
ionization structures as well as making for an interesting looking image.

Note that there is none of the OIII data in this shot: nothing shorter
wavelength than Halpha is in this shot.

Here is the Crab shot:


http://www.rdcrisp.darkhorizons.org/...N2_ha_page.htm