On Fri, 08 May 2009 03:26:42 GMT, Davoud <star@sky.net> wrote:

From the standpoint of transmission it doesn't matter. Some filters have
an AR coating on one side; it yours does, face it towards the sensor. In
general, face the side that is less reflective to Ha towards the sensor.
That's probably the red side, but you may need to test it to be sure. If
there isn't much difference, it will be hard to tell (and therefore not
really matter).

The reasoning behind this is that the most likely source of halo-like
artifacts is light reflecting from the sensor or its cover glass, back
to the filter, and back to the sensor again.

Chris L Peterson
Cloudbait Observatory