Hydrogen-Alpha Filter vs Red Filter for Astro Imaging
I decided to up the stakes and I purchased a second hand QSI 583wsg camera with a full set of Astrodon RGB and Narrow-band filters.
I have only ever used one shot colour cameras in the past. Either an Canon 40D or the QHY8 cooled camera. The QSI is my first mono camera.
I have only spent a couple of nights using the camera but what amazed me about using the Ha filter is that even though the Hydrogen Alpha filter captures a much narrower portion of the red band (hence the narrow-band name), for the same amount of time it revealed much more nebula data. Below are two images; both are a single 5 minute exposure on the same night The first is with the Astrodon red filter, the same is with the Astrodon 6mm Ha filter. Although the HA reveals less stars it shows a lot more of the nebula.
I have also included a spectrum from the Astrodon Site to show where the H-Alpha filter sits compared to the standard Red filter
If you click on either of the images below, they will be displayed in a pop-up that will allow you to toggle between the two images for comparison. It really does highlight the difference the HA filter can make.
Eta Carinae nebula with Red FilterThis is a shot of the nebula using a standard red Astrodon filter
Eta Carinae nebula with HA FilterThis is a shot of the nebula using a Astrodon HA filter
The image below shows the difference between the HA filer and the Red filter on the colour spectrum. The OII H-Alpha and SII entries show the filters used for narrow-band photography. Often referred to as the Hubble Pallet.