Originally posted by Eric Seavey You take a photo of the subject, and then you move the camera a little such that there are vey few stars in the frame. Then you unfocus the camera and take a photo. In photoshop you take the blurry image and add it as a layer and select difference to reduce the light pollution.
Very interesting.
I don't do astrophoto, but I have some friends who does. And two years ago, I thought if that something alike can be done, photographing the sky with a Sodium pass filter, and a Mercury pass filter, and than extracting the light pollution in Sodium and Mercury, exactly in the same way you did.
I didn't have those filters to try this, but I still think it can be done.