How close can you go? Shooting Ha with bright moon nearby....

[geoflewis]

Hi all,

I'm fairly new to shooting Ha and have read varying reports on its tolerance to moonlight, so what do you NB experts say please? I have a forecast clear night tomorrow and was thinking to go after the Rosette Nebula (NGC2244), hoping to add RGB next month, but a 90% Moon will be within 10-15 degrees, so would this be possible, or a crazy idea...?

TIA, Geof

[DaveS]

I'm in the same situation, and even with 3nm Astrodons I wouldn't try it. Maybe at 60 deg or only 50% moon at 30 deg.

But I also have LP to fight.

[geoflewis]

 

1 minute ago, DaveS said:

I'm in the same situation, and even with 3nm Astrodons I wouldn't try it. Maybe at 60 deg or only 50% moon at 30 deg.

But I also have LP to fight.

Thanks Dave, well mine is a 6nm Astronomik, so I'll take that as a no and look for a different target. Cheers, Geof

[pipnina]

19 minutes ago, geoflewis said:

 

Thanks Dave, well mine is a 6nm Astronomik, so I'll take that as a no and look for a different target. Cheers, Geof

Try taking a single sub of it in Ha, and doing another target like you say, then compare with another single Ha shot during moonless night. You'll have actual reference on how much the moon will effect your image

[geoflewis]

3 minutes ago, pipnina said:

Try taking a single sub of it in Ha, and doing another target like you say, then compare with another single Ha shot during moonless night. You'll have actual reference on how much the moon will effect your image

Thanks pipnina, thats an excellent idea .

[swag72]

I did some work on the moon's effects, specifically with the luminance filter. I was surprised to see that if you mix moon affected and non moon affected data (I did it at a 50/50 split) there was no significant damage done to the end stack when compared directly with an equal amount of moon free data.

If you are using Ha then that will change the overall effects...... theoretically in your favour. I was surprised as I thought that luminance under moon light would be a big no-no..... so Ha in my opinion is definitely worth exploring ??

[pipnina]

4 minutes ago, swag72 said:

I did some work on the moon's effects, specifically with the luminance filter. I was surprised to see that if you mix moon affected and non moon affected data (I did it at a 50/50 split) there was no significant damage done to the end stack when compared directly with an equal amount of moon free data.

If you are using Ha then that will change the overall effects...... theoretically in your favour. I was surprised as I thought that luminance under moon light would be a big no-no..... so Ha in my opinion is definitely worth exploring ??

So it didn't increase gradients? Or it did but was easy to fix?

[geoflewis]

1 minute ago, swag72 said:

I did some work on the moon's effects, specifically with the luminance filter. I was surprised to see that if you mix moon affected and non moon affected data (I did it at a 50/50 split) there was no significant damage done to the end stack. 

If you are using Ha then that will change the overall effects...... theoretically in your favour. I was surprised as I thought that luminance under moon light would be a big no-no..... so Ha in my opinion is definitely worth exploring ??

Hi Sara, I appreciate your insight and experience. I've been looking around Stellarium for other possible targets, without too much success, as my NW-NE horizon has trees to about 60 degrees elevation so are you suggesting that I just go for it....? Do you think 6nm is up to the challenge? I was thinking to maybe shoot M81/M82 pair Ha, but don't know if that's a suitable target to add LRGB data later. Many thanks, Geof

[DaveS]

Well, give it a go, the Rosette is fairly bright in HII.

I've got N & O to get. Not moon-proof, even at 3nm.

[swag72]

4 minutes ago, pipnina said:

So it didn't increase gradients? Or it did but was easy to fix?

I found that the biggest difference was lack of contrast and noise..... but when combined with non moon affected data there was no significant difference.

[tomato]

That’s encouraging to hear Sara. A big driver for buying a Ha filter was to increase my possible imaging time under UK skies. I will be training my rig on the Horsehead tomorrow night if we get a clear spell in North Yorkshire, even if the moon is only 20 degrees away.?

Note, currently blowing a gale and thick cloud....

[swag72]

4 minutes ago, geoflewis said:

Hi Sara, I appreciate your insight and experience. I've been looking around Stellarium for other possible targets, without too much success, as my NW-NE horizon has trees to about 60 degrees elevation so are you suggesting that I just go for it....? Do you think 6nm is up to the challenge? I was thinking to maybe shoot M81/M82 pair Ha, but don't know if that's a suitable target to add LRGB data later. Many thanks, Geof

I'd  say just go for it.... if the data isn't good enough it will be binned.... but you wouldn't have had any data if you'd not tried! 

[geoflewis]

1 minute ago, DaveS said:

Well, give it a go, the Rosette is fairly bright in HII.

I've got N & O to get. Not moon-proof, even at 3nm.

Think I might as well. Ha is my only NB filter and normally used to enhance red channel, but last time out I also used it as lum on IC443. Was going to shoot more of that but the Moon is literally right on top of that tomorrow...!!

[geoflewis]

1 minute ago, swag72 said:

I'd  say just go for it.... if the data isn't good enough it will be binned.... but you wouldn't have had any data if you'd not tried! 

Well that's true enough

[alexbb]

I tried a couple of months ago to shoot a panel in Orion through a 7nm Ha filter when the moon was bright and close and ended with deleting the data soon after stacking. Compared to the other moonless or moonaway panels, it was lacking details and I could not lift the levels high enough to combine the panels uniformly. If you image a single panel, you can get away with this, the result will be just an image with a lower SNR compared to one without moon, but still high enough to be usable.

On the other hand, if you plan to shoot LRGB on M81 and M82, you can bring some additional details with Ha.

[geoflewis]

14 minutes ago, moise212 said:

I tried a couple of months ago to shoot a panel in Orion through a 7nm Ha filter when the moon was bright and close and ended with deleting the data soon after stacking. Compared to the other moonless or moonaway panels, it was lacking details and I could not lift the levels high enough to combine the panels uniformly. If you image a single panel, you can get away with this, the result will be just an image with a lower SNR compared to one without moon, but still high enough to be usable.

On the other hand, if you plan to shoot LRGB on M81 and M82, you can bring some additional details with Ha.

Thanks Alex, decisions , decisions...., we are getting so few clear nights in the UK recently that I don't want to waste them. Rosette will be a single panel so sound like it will work, equally I've not yet imaged M81/M82 with my CCD camera, so it's good to know that shooting Ha there will add details to LRGB data when I do go for that. Cheers, Geof

[alexbb]

I will try to image this and tomorrow evenings a panel around rosette. I hope to match the SNR of 4 hours with moon with the SNR of 2 moonless hours. I will let you know how it turns out, though I don't know if I can measure the SNR properly since the Rosette has plenty of hydrogen, while the surroundings have less.

[geoflewis]

Thanks everyone for your feedback. Well tonight I decided to go for it and captured just under 4 hours of Ha data on the Rosette (NGC2244). Unfortunately not only was the Moon bright, but there was a lot of high hazy cloud, but I stacked 20 of 23 10 min subs for just under 3.5 hours integration. I think there are some artefacts, not sure if they are cloud induced or something else, so I'll need to blink through the subs to see if I can get a cleaner stack, but I wanted to share the result so far.

I guess the conclusion is that the Ha filter does a pretty darn good job cutting through (or cutting out) moonlight - well I'm pretty pleased with the result, but will have to see how well it blends with LRGB when I get around to shooting those.

Cheers, Geof

[alexbb]

I've 3 hours now on the left panel from this evening and yesterday evening. Almost full moon, very close to the target. 2 hours on the right panel with 50% lit moon, more than 90 degrees away from the target. You can see that there's a lot more signal to the right panel compared to the one on the left:

[geoflewis]

32 minutes ago, moise212 said:

I've 3 hours now on the left panel from this evening and yesterday evening. Almost full moon, very close to the target. 2 hours on the right panel with 50% lit moon, more than 90 degrees away from the target. You can see that there's a lot more signal to the right panel compared to the one on the left:

Hi moise212, thanks for sharing that 2 frame panel, it clearly shows the adverse impact of the bright moon. I had that grainy effect in my 3 hour stacked image from last night, but nothing with which to compare it, so your post is very helpful. Regards, Geof

[alexbb]

I was able to fix this. The streaks were due to noisy flats. However, the same master flats/darks/bias were used for both panels. I didn't change anything in the setup.