M42 HA What The?

[Tandum (Robin)]

We finally had a clear night up here in Brisbane and I got a chance to plug in the Badder HA filter I bought in October

I think something is wrong, either in the way I use it or in the filter itself. I've attached the raw red file out of the camera and the PS converted greyscale file. This is a 6 stack of 20 minute subs @ iso 400, flats/bias/darks applied.

Why has the grey image lost detail and gained noise? The original image showed blue and green in the Hystogram and I didn't expect that either. However this is my first HA shot which I was going to mix with RGB data.

[Garyh]

Hi Robin,
I can`t really help but have you tried just extracting the red channel as a separate image? and saving that?
cheers Gary

[multiweb (Marc)]

That looks about right Robin. The Ha goes in the red pixel in the bayer matrix. There's always a bit of noise in the blue and a slight signal in the green. I don't know about your camera sensitivity at ISO 400 but for 6x20min subs it didn't pick up much signal. Maybe bump up the ISO and try again? But the final stack looks about right.

[Tandum (Robin)]

Splitting the image helps, the blue channel looks like it's all noise. This one was 15 minutes @ 800 and shows more data. Looks like there's a lot more fiddling to do with this thing, if the weather ever clears up

[AlexN]

Feed it ISO.. You really are wasting time doing ISO400 subs...

ISO800 + 20 min subs with Ha wont be a problem... Remember, Light pollution is not going to ruin these exposures.

Ps - 15min at ISO800 would have more detail and nebulosity than a 20min ISO400... 15 @ ISO800 = 30 @ ISO400.

The data itself looks good, and its good to see you have that EQ6 under control... Looks fantastic..

As the others said, always extract the red channel, Its the one with the useful info, the green and blue channels are nonsense...

Good goin mate.
Alex.

[gregbradley]

The chip has a matrix of red green green blue dyed filters in a grid of 4 over 4 pixels in a square. This is repeated over the surface of the chip.
So the green channel will most likely be noisiest.

I always used absolutely max ISO when using a DSLR as they are less sensitive than a cooled CCD and that is one advantage they do have which is the abillity to change the sensitivity of the chip (I believe ISO simply changes the amplification of the signal received).

Some like to do ISO800 to get deeper with less noise.

for a 20 minute exposure you would want to see a lot more of the neb than is showing in your image.

By the way M42 isn't really that nice in Ha and other targets are nicer. Just an opinion.

Greg.

[AlexN]

True, M42 responds better to OIII than Ha, Slew slightly towards the north and down a bit, and point that Ha setup at the Horse head. Ha + The Horse = Awesome.

[Tandum (Robin)]

Cheers guys,
I just pointed it at the most obvious thing in the sky to get some results for a first run. I have a 2" filter but it doesn't screw into anything. I have it between the camera adapter and the reducer. It sits in there securely but it's not actually screwed onto anything. I was a bit worried it was back to front

If it ever stops raining I'll have another go. Maybe next year by the looks