H Alpha filter query

could it be some sort of noise thats generated when the CCD is read.??

I hope not or Kieran has a big problem. Readout (bias) noise can be ruled out by taking a very short shot (shortest the camera will allow). If the banding is not there then it ain't readout noise.

So Kieran is that the 6nm or the 13nm version you have?

Problem sourced. The cause was a light leak from.............the moon. The filter wheel was orientated at just the right angle to allow moonlight to get in behind the H alpha filter. I assume the banded effect is due to an internal reflection aswell.

That's great news Kieran, glad you resolved it !