that I hate to see part of it blocked by filtering. Odds are there are interesting things out there at the same frequency range that you won't get to see because of the sodium filter.

Don't get me wrong, filtering is certainly better than nothing, but perhaps there's a better way to reduce the effects of light pollution on astronomy telescopes. A coworker of mine is a good amateur astronomer as well as a really good programmer. We've discussed an old idea of mine (it came to me in 1982) that just might work better than filters. Unfortunately, I don't have the equipment to test this idea, but I still hope to test it one day. The idea is based on a few assumptions. If the assumptions are proven wrong, then of course the idea is DOA.

1. All lights powered by AC flicker at the same frequency as the line (60 Hz in the US, 50 Hz in many other places).

2. At 60 Hz, the wavelength of the flicker is 5000 KM. That suggests that all of the lights in a given region are flickering in phase. Power companies are very careful to keep everything synchronized.

3. It should be possible to detect a 60 Hz component in the background light pollution.

If these assumptions are true (and it shouldn't be all that difficult to test them), then it should be possible to reduce the effects of the light pollution by sampling the light near the nulls of the sine wave. Originally, I thought that it would be possible to synchronize the samples from a CCD near these nulls then assemble the images using a technique called speckle interferometry. However, my coworker suggested a simplier technique. He suggested using an LCD shutter to shoot around the nulls.

Being an airplane nut, the analogy I use to describe this technique is that of an interrupter gear on an old fighter plane. Back in WWI when they started mounting machine guns on planes, they had a problem with bullets striking the propellor. Anthony Fokker invented an interrupter gear that stopped the gun from firing when a prop blade was in the way. My idea is to stop the light gathering when the light pollution is at the peaks of intensity, effectively shooting between the blades.