Using Filters

Our online training has a comprehensive course that gives further details about using filters to make colour images and images that show different scientific information. 

Filters

If you have been reading through other pages in the "Advice on Using the Telescopes" section you will have realised that imaging with a telescope has many similarities to taking images with a digital camera. There are also some considerable differences. One of these is the way in which filters are used and colour images are produced.

In addition to making standard colour images it is also possible to use the various filters available on the FTs for other work. The filters available to you are:

M16 - The Eagle Nebula

The image below shows a comparison of what the same image looks like in colour and then all of the seven individual filters.

It is quite easy to see that different things are visible in various images. Most obvious are the larger number of stars visible in the infrared image and the gases that are more visible in the H-alpha and OIII images. The top left images shows the result when combining the B, V and r' images to make a standard colour image.

M27 - The Dumbbell Nebula

In this image it is very clear that the infrared filter is able to see stars that are being hidden by the gas and dust in this nebula in some of the other filters.

The H-alpha and OIII filters are regarded as narrow band filters and generally show up areas where energetic processes are ongoing. These two filters show light being emitted by particular gases, such as ionised hydrogen or oxygen. These gases show where interesting things are happening, as they have been heated or excited in some way. The sorts of things they would show are shock fronts in planetary nebulae, supernovae and accretion discs around black holes. You can find out more about when to use these filters in the various projects and activities on this website.