Hydrogen Alpha Filters

To add to my equipment list (as you do), I decided to get a more sensitive Monochrome camera and a set of Narrowband Filters.

When I first entered this hobby I used one shot colour cameras in the past. Either an Canon 40D or the QHY8 cooled camera. 

Mono cameras don’t do colour, as you can see from the images below. But this give a few advantages, such as being more sensitive and give sharper pictures (due to the fact that in colour cameras there are pixels next to each other for each RGB colour, so you get slightly reduced resolution per colour and the camera interpolates the pixels in between).

You still can create colour images with a monochrome camera, but you need to take individual pictures through different coloured filters and merge them, post processing to make the coloured image.

This does mean though that your are not limited to Red, Green, and Blue, light like a colour camera. You can use all sorts of specialised filters to pick very specific bandwidths of light.        

What amazed me about using a narrowband Ha (hydrogen Alpha) filter, is that even though the Hydrogen Alpha filter captures a much narrower portion of the red band (hence the name: narrow-band), for the same amount of time it revealed much more nebula data depending on the target you are imaging.  

The chart below shows the typical narrowband filters that are used for astrophotography. As you can see they only allow light in from very specific narrow areas of the spectrum.  If you have ever seen pictures taken by the Hubble telescope, you have probably seen narrowband images. They often reveal more detail by showing light from specific wavelengths emitted by Hydrogen, Sodium and Oxygen. Colour pictures taken with these filters are often presented in what is called the Hubble Palette.     

Below is an image of the Eta Carina nebula taken with a mono camera. There are two variants. Each is a single 5 minute exposure taken on the same night. The first is with a standard Photometric red filter, the second is with an Astrodon 6mm Ha filter.  You can toggle between the two images by click on the right arrow on the side of the image. 

Although the HA shows less stars, it shows a lot more of the nebula.