Infrared Questions

[multiweb (Marc)]

Been doing a bit of IR imaging now and just a few things I've noticed that I'd like to run by our more scientific crowd here. I've double checked last night again just to make sure that I wouldn't say anything stupid.

My FWHM was getting better as the DSO I was imaging was getting lower in the western horizon. Doing LUM FWHM degrades really fast as you go lower. Not IR. I could still have a strong signal. I lost the guide star in the muck and that's what stopped me but the last subs were still very good. So I'm thinking that if the guider was also going through the IR filter (OAG) I might have been able to keep going.
PS: I had also a balance issue being West heavy so the guiding got better as the counterweight was going down.

Similarly last month it clouded over. I lost the guide star intermittently. But I picked it up again so the subs weren't affected. Funny thing is that the subs weren't affected at all by passing clouds. If I did LUM they would have been washed out.

Does this make sense? or ... am I imagining things?

[cometcatcher (Kevin)]

I'd just like to chime in to say thanks for the idea. It's so hazy here I haven't been doing anything astro. I think even red or Ha would cut through the haze better than wide band.

[multiweb (Marc)]

Originally Posted by cometcatcher

I'd just like to chime in to say thanks for the idea. It's so hazy here I haven't been doing anything astro. I think even red or Ha would cut through the haze better than wide band.

Hi Kevin, IR is good value. Did these last night and the night before. Hazy Wednesday with a bit of moon but still no problem. Even less subs than Ha. I can do 1h on each panel. In Ha would take me at least double that to get a good SNR plus when the air is moist skyglow gets worse. With IR I'm less affected and can just boost contrast to match subs taken at the zenith with the ones taken closer to the horizon with almost no resulting noise.

[jahnpahwa (JP)]

Originally Posted by multiweb

Hi Kevin, IR is good value. Did these last night and the night before. Hazy Wednesday with a bit of moon but still no problem. Even less subs than Ha. I can do 1h on each panel. In Ha would take me at least double that to get a good SNR plus when the air is moist skyglow gets worse. With IR I'm less affected and can just boost contrast to match subs taken at the zenith with the ones taken closer to the horizon with almost no resulting noise.

Digging this thread right up from the archive.


Marc and any others, do you have any experience to share on which band pass is best for different targets? I'm realistically only interested in DSOs for now, though if the same pass works for planets and the moon that'd be fine too I find it totally amazing that there are so many stars visible in IR and not in R.

[multiweb (Marc)]

Originally Posted by jahnpahwa

Digging this thread right up from the archive.


Marc and any others, do you have any experience to share on which band pass is best for different targets? I'm realistically only interested in DSOs for now, though if the same pass works for planets and the moon that'd be fine too I find it totally amazing that there are so many stars visible in IR and not in R.

Oh wow, it is a little while ago and fuzzy. Looks like lenses and widefield imaging. And the links are dead. I ll have a look at the files, fix them and figure out the bandpass.

There's more recent stuff from astrofest 2018 I believe in bicolor.

[multiweb (Marc)]

Originally Posted by jahnpahwa

Marc and any others, do you have any experience to share on which band pass is best for different targets? I'm realistically only interested in DSOs for now, though if the same pass works for planets and the moon that'd be fine too I find it totally amazing that there are so many stars visible in IR and not in R.

Ok here's the two filters I used; Baader L filter and Astronomik Pro Planet 742nm. You can see the LUM cuts sharply at ~700nm and the IR starts at 720 and peaks quickly at 740nm and onwards. So there is no overlap with these two. If you use a Sii that cuts off at ~680nm you can also do some cool blends. So once you have your channels you do L IR/L IR or IR IR/L L or replace the L by the Sii.

If you wanted to do pure IR you'd use NB IR filters at 750nm, 800nm, 850nm, 900nm etc... provided your camera QE is still high after 700nm. NIR NB filter can be quite expensive as well.