Synthetic Luminance....one more time....what about rejection?

[pfile]

well... something like 75% of the baryonic matter in the universe is hydrogen, so it stands to reason that Ha sources will be bright owing to the abundance of hydrogen. basically if you want to get better SNR on O and S, you simply have to have longer integration times, since the available signal in O and S is much, much less than Ha.

rob

[RickS]

Very interesting.  I have to think this through.  I am collecting data on a couple Milky Way nebula in Ha, O and S and just integrated some 30 images each and the noise is way different just to the eye... using the same parameters.  This would be an interesting test.  The Ha was way less noisy that the other two and I was saying to myself, how am I going to get the backgrounds to look the same... was thinking what noise reduction and masks to use.  Maybe would be smarter to get the integration better then there would be less noisy images...

As Rob said, most objects are usually brighter in Ha than OIII or SII and collecting more data at the dimmer wavelengths is the best way to match noise levels.  If you don't have the luxury of doing that (or can only partially do it) then I find it helpful to do noise reduction separately on each so I can hit the noisier masters harder.

Cheers,
Rick.

[jerryyyyy]

I find all this interesting.  I am going to post later today the Rosetta nebula in H-alpha which is nice and smooth with 32x300s subs, but I have the same amount of subs in O-III and S-II and they are salt and pepper backgrounds.  I guess I am just going to need to double the number of subs on these... long term project even with the Tak 180.  I only get about a 2h good window in my backyard/night for any DSO... so that translates to 24 300s/5minute subs.  Wish I had more time to figure out the optimal approach to all this... seems I have calculated and recalculated what I need to do, but that varies for each object depending of how much signal there is in each channel. 

Image in question:

[pfile]

"if you want a vision of astrophotography, imagine a camera exposing the sky - forever." to paraphrase george orwell 

[jkmorse]

Rick,

Have you seen any downside to noise reduction on each filter stack individually?  I assume you are using MLT in the linear phase but if not can you expand on your technique.

Thanks,

Jim

[RickS]

Have you seen any downside to noise reduction on each filter stack individually?  I assume you are using MLT in the linear phase but if not can you expand on your technique.

Hi Jim,

I don't think there is any downside.  It's certainly better than applying the same amount of NR to all three channels if they have widely differing SNR.  I do use MLT, normally with a linear mask.

Cheers,
Rick.