This is a new one for me, and it's a direct result of terrestrial imaging (i.e. standard photography). Looking at accessories for my Canon 40D I spotted some interesting filters which are obviously standard for photographers wanting to do infrared photography - namely R72 filters. Now these have some useful applications in deep-sky imaging as well!
R72 filters only let through light of wavelength longer than 720nm, and the Silicon CCD sensor has a cut-off around 1,000 nm so the filter allows through a relatively broad band of near infrared radiation. Unfortunately it is just beyond H-alpha radiation, so you don't get the main radiation source from emission nebulae, but it is useful to work at longer wavelengths as you will be able to see stars "through" dust and nebulosity.
The image here:
http://img85.imageshack.us/my.php?image ... alfvq0.jpg
shows the familiar M42, the Great Nebula in Orion imaged in the near infrared through an R72 filter. There are a lot more stars clearly visible in the nebula itself than are apparent in visible images.
The one-shot colour camera I use (SXVF-M25C) has a very poor quantum efficiency in the near infrared, so a mono camera with higher QE would give a better result. If anyone out there has a good mono CCD, try some deep-sky imaging with an R72 filter, this work doesn't seem to have been done much before.
Nexstar 11 GPS, 2 x Sky 90, M25C, MaximDL, Photshop CS3, Noel Carboni's Photoshop actions, 7 foot Pulsar fibreglass dome, Canon 40D, 100mm macro lens, 28-200mm zoom lens, 17-55mm f#2.8 zoom lens, 100-400mm zoom lens, 1.4x converter, 2x converter.