DSLR flats with Ha filter

[Shibby]

I'm having trouble getting correct flats through my Ha filter, I'm not sure how to expose or stack them correctly, which has left me scratching my head...

To get the average histogram half-way takes a 10s exposure, but obviously the red histogram is way off the scale so I assume this won't caibrate properly? To get the red histogram half-was takes an exposure of 0.5s, so I took a set of these and tried stacking these in DSS but of course the (mono) result is too dark due the the G and B components. Am I right in thinking that an over-exposed red channel will ruin the flat?

Do I perhaps need to open up all the RAWs in PS, remove the G&B channels and re-save, or am I missing a trick here with DSS?

Thanks for any help!

[rfdesigner]

How about not worrying about the G and B at all?

you'll be getting very little signal in them so simply flat for red, then when you convert from CFA to RGB, chuck the G & B in the bin.

You might even want to make a G & B blanking mask so you make sure you have no data at all in the G & B pixels before converting to RGB.

Derek

[dugpatrick]

When using a H-alpha filter I only look at the Red part of the histogram. I aim for 2/3 of the way from left to right. Green and Blue are on the far left and probably clipped. This method seems to work well for me.

Doug

[Sp@ce_d]

Hmm.. I've never noticed a problem. I use a Gerd Neumann EL panel, set the canon to AV mode & fire away.. seem to work out ok. Normally stack using DSS or Nebulosity.

[Shibby]

Thanks for the responses.

I found that the flats (exposed for red channel) worked ok in the end, but only if I stack them each time along with the light frames (I can't use a saved master flat).