Not being a scientist I had problems in relating the wavelengths of the light with the colours visible to the human eye.
The above spectrum chart helped me a lot to understand the transmission graphs of my filters.

Transmission Baader UV-IR-Cut. And here is Robin Leadbeater's IR FAQ

1,25" Baader Contrast Booster. Transmission Baader Contrast-Booster.

I bought this filter to image emission nebulae AND to fight my local light pollution.As this filter is also a 'light absorber' the exposure times are much longer. More about the Astronomik H-Alpha Filter.

I received this filter as a gift but right now I have not yet used it. Here you can read more about the Astronomik H-Beta Filter. On the internet I found the following information about the H-Beta Filter from the competing Lumicon brand: This filter is so specialized, it is really only good for two objects; IC 434, the emission nebula surrounding the Horsehead Nebula in Orion, and the California Nebula. Both of these objects emit strongly in the hydrogen beta portion of the spectrum. While it is possible, just barely, to catch a glimpse of the Horsehead without the H Beta, the view with it is far more stunning. The filter emphasizes the glow of both of these nebulae, turning them red. In the case of IC 434, the red outline around the actual Horsehead itself (B33) is what makes it visible. The California Nebula is similar in that it is just barely visible without the H Beta. With it, the California "shape" becomes clearly visible. This filter can also be used for viewing some nebulae; unfortunately most of them are quite faint. Source of the above.

I bought this filterset to use in combination with my monochrome cameras Astronomik gives a lot of information and also a transmission graph. I consider the parfocality a very important issue.

Home made Moon Filter [for visual use only] When looking at the moon through an eyepiece I usually am a bit blinded by the very bright glare, which also disturbs the visual observation. My good friend Tom How once told me that he uses a pair of sun glasses: like me he loves to make things rather than buy them. I went to the DIY shop and bought a PVC tube coupler: inner diametre 40mm, so that the tube nicely fits over an eyepiece. With a hacksaw I shortened the PVC tube coupler and with a pair of scissors I professionally destroyed one of the plastic glasses of an old pair of sun glasses. Last night - January 1, 2007 - I used the filter for the first time and I am quite happy with the result. I just did some last finishing work: you can see still static plastic particles here and there :o)