Histogram exposure for narrowband flats

[Jannis]

Usually when i take flats, i just setthe camera to aperture-priority and let it set the exposure - but with narrowband this didn't seem to work so well?
With the Ha filter for example, i noticed the red channel reaching almost the top of the histogram, and with OIII the green. Although the "total" histogram showed OK at 1/3-1/4 or so.

So just to confirm, should i expose acording to channel the filter is for, or the total?

[ultranova]

Hi You should be looking at  the same Histogram level  for all

your filters, the camera on aperture priority should take care

 of your exposure times, your histogram levels should all look roughly the same

on all your filters

Paul

[D4N]

I guess you are using NB filters on a colour camera then?

I would say that the total histogram is meaningless in this case and that you need to pay attention to the channel you are actually exposing.  Aperture priority is probably not well designed for exposing a single channel, I would guess that it is averaging the channels which is why it is over exposing.

[Jannis]

Thanks for the replies!

Indeed i am using NB filters on a color camera, and after some testing i came to the same conclusion. I had best results exposing acording to the histogram for the spesific channel instead of letting the camera run in aperture-priority as it was overexposing to compensate for the lack of light in the blocked channels.