Narrowband Imaging

Narrowband imaging is a tool Astrophotographer’s use to take high contrast images of certain objects in the night sky. Narrowband imaging is so called because the filter only allows light at very narrow bandwidths to pass through. Most Nebulae emit the majority of their light in specific wavelengths and narrowband filters are designed to only let this light pass through them which will show amazing clarity and previously hidden features that are too faint for normal RGB (red, green & blue) imaging. These filters will inhibit or severely reduce any polluting factors like the Moon and light pollution caused by street lights. In turn this darkens the background and shows more clarity in the object being imaged. There are four main narrowband filters, Hydrogen Alpha (H-a), Hydrogen Beta (H-b), Singularly Ionised Sulphur (S-II) & Doubly Ionised Oxygen (0-III). As of this moment, I only own an H-a & 0-III filter but will be adding more to my collection as and when. If you want to get in to narrowband imaging you will need to have a decent tracking mount that is guided. The exposure times required are very long indeed - where a normal RGB exposure using a DSLR is in the region of 2 - 5 minutes, when it comes to narrowband expect your individual exposure lengths to start at 10 minutes and can go up to as long as an hour. Some expose for even longer!! The images of the Rosette Nebula above is my first attempt at H-a imaging. The black & white image is the pure H-a image with the colour image being what is called an Ha-RGB which is an integration of both the H-a image and an image taken about a year ago in standard RGB through my DSLR. They are then stacked and processed separately and then merged together. This gives the detailed clarity and hidden features of the Ha along with the colour of the RGB all in one image. This picture shows the difference between the normal RGB on the left and the enhanced qualities once the H-a has been integrated on the right. I will be adding Ha-RGB images to this page as I take them which in the UK is dictated by the amount of cloud cover.
© Paul’s Astrophotography 2020