Different filters can perform quite different functions:
- Neutral filters suppress the light from bright objects. These filters are available as simple Moon filters, grey filters or variable polarising filters.
- Colour filters increase the contrast of certain structures when observing planets. They are therefore often referred to as planetary filters.
- There are also special colour filters for astrophotography, usually as L-RGB filter sets.
- Nebula filters, also known as interference filters, block parts of the spectrum. This can, for example, suppress light pollution and increase contrast (UHC and CLS filters). Line filters only let light from specific spectral lines pass through, and are ideal for observing astronomical nebulae.
- Blocking filters block the light from a certain wavelength, pass filters on the other hand let it through. For example, a UV blocking filter can suppress harmful UV rays.
The correct choice of filter will considerably increase your telescope’s range of applications.