Astro photography with a Light Pollution filter

I live in a heavily light polluted area between Bournemouth and Poole on the south coast of England.

To show you how bad it is, checkout this single 160 second image of Messier 3 taken with my astro-modded Canon 40d. Even though much of the street lighting has been upgraded to white LED down lighters rather than the old sodium lights, you can see its still a problem. The unwanted light pollution bloats the stars and hides some of the detail.

     

This second image was taken using the same camera and settings with only one difference.I inserted an Astronomik CLS Visual Light pollution Clip-Filter

The filter is 1 mm thick and made of glass. Simply push it in place in front of the sensor and its ready!

This is how the filter works (I will try to keep it short).

Visible light is measure in wavelengths from 400 to 700 nano metres. To give you an idea where the colours are, Blue is 425nm, Green is 510nm, Yellow is 570nm and Red is 650nm.
The orange type of artificial light pollution, say from street lighting ranges from 525 to 620. Whilst blue light pollution from LED's such as the new street lighting is 418nm. All of these wavelengths need to be blocked by the filter.
The filter allows through over 90% of the following wavelengths that come from space.
425nm to 520nm and 620nm to 700nm.
Specific wavelengths often needed are;
H-Alpha 656nm  from red emission nebulae

H-Beta and O-111 for enhancing blue objects