Peter Kinchington's Carina
Peter Kinchington sent me this dramatic image of the Carina Nebula in narrowband a while back. He took it using an ED80 refractor from his place in Mooroolbark (not far from the shop).
For those of you who are used to seeing Carina as pink, this is a false colour image, using the "Hubble Palette". Peter has used a monochrome camera (in this case, a QHY163M) which captures the light produced by ionised Hydrogen, Oxygen and Sulphur in the nebula.
Visible light is made up of a whole spectrum of wavelengths from different sources. A good number of these sources are ones we don't want. For example, normal DSLR photos pick up extraneous light from terrestrial light pollution from street lights and your own house. It'd be nice to be able to get rid of this light.
On the other hand, you really do want the light from (say) ionised Hydrogen, because this makes up the bulk of gas in most nebulas. Using the correct filter, you can. Ionised Hydrogen shines in a highly-specific wavelength - about 656 nanometres. Peter has used such a filter to exclude all light above and below this wavelength. Peter's image uses Hydrogen, Oxygen and Sulphur filters to capture the wavelengths he needs.
If you've seen a photo of the Carina Nebula taken with a colour camera, you'll notice it has a pinky colour. Peter uses a monochrome camera - a QHY163M and shoots through filters that give him the components he can use to build a colour image. But it's not a "true colour" image.
Ionised Oxygen shines as a teal colour, and Sulphur, like Hydrogen, is a shade of red. In the final image, the Oxygen light shows as blue and the Sulphur shows red, but the Hydrogen is shifted to green light. This gives the photo that "false colour" look.
Finally, the Carina Nebula is a large target. The get it all in, you need a short focal length and a large sensor. Peter's field of view isn't as large as this, so his image is built of four panels stitched together. that's quite a task.
Thanks for the image, Peter!