Narrow band filter ratios for imaging

[White Rabbit]

Hi guys.

Is there ratio in terms of length of subs for narrow band images or does it depend no how much of each gas is present in any give cloud?

I'm taking Ha SII and OIII on eta car and in comparison to Ha there isnt much SII and OIII so do I take longer subs for those filters?

Thanks

[pluto (Hugh)]

Originally Posted by White Rabbit

Hi guys.

Is there ratio in terms of length of subs for narrow band images or does it depend no how much of each gas is present in any give cloud?

I'm taking Ha SII and OIII on eta car and in comparison to Ha there isnt much SII and OIII so do I take longer subs for those filters?

Thanks

I think it depends on the particular nebula but last time I did Carina in NB I did 5 min subs for Ha, mostly 5 min subs for OIII plus a few 10 min and lots of 10 min subs for SII. I also find the filters react differently to light pollution (SII and especially OIII I think have a much higher background level than Ha when I image in the city) so sometimes I need more subs to compensate.

[RickS (Rick)]

There's no magic formula. Generally Ha is brightest but the amount of OIII and SII varies hugely depending on the object. You'll normally need to do longer subs and/or more of them in OIII and SII to get SNR even vaguely approaching that of your Ha.

I use constant length subs, typically 30 mins, and use the PI noise analysis tools as a guide to figure out the number of subs I need in each filter.

Cheers,
Rick.

[White Rabbit]

Thanks guys, I've been doing 10min subs. So I'll maybe do a lot more for SII and OIII.

cheers.