Narrowband imaging - Deciding on how many subs

[swag72]

Having recently decided that I like narrowband imaging, I have 3 finished items so far. The first one was clearly a fluke and worked out just how I wanted it (after much help from here) lots of yellows and cyans. The other 2 images have lacked those lovely bright colours and I have struggled to repeat my inital fluke!

So fast forward to NB image number 4 for me and I am banging my head against a brick wall again. I have the following subs for NGC7635 (Bubble nebula)

Ha - 14x1800s

OIII - 13x1800s

SII - 12x1800s

So far, this totals almost 20 hours, but the data would suggest otherwise. I am struggling with the blue (again) and have so little of it.

So, have I got enough data / subs? Do I need longer subs?

I am imaging using my Pentax 75SDHF at f6.5 and my Atik 314L+.

How do you determine the amount of data required for the OIII and SII in particular? Is there a general consensus that x amount of OIII and SII is required for y amount of Ha? The Ha is definitely very strong.

[Ant]

I try work to the ratio 1:2:4 for Ha, OIII and SII respectively. I tend not to change the sub length, but go for 10 x 20m for Ha then 20 x 20 for OIII etc etc.

I think it was Black_Cloud that did some work on ratios for NB imaging where sub length was altered... with some very interesting results.

Cheers

Ant

[swag72]

Cheers Ant.

Anyone else any thoughts? There's some cracking NB imagers out there - Care to share your secrets?

[martin_h]

1:2:3, depending on target, some are very lacking in SII so may need more time spent on that filter. All my subs tend to be 20 mins in duration, you dont need an awful lot of Ha to swamp out the image.

[swag72]

Many thanks for that Martin - Just the sort of thing I was looking for. What kind of minimum Ha data would you consider for a NB image. Given these ratio's it's very tempting to do a couple of hours Ha and that's it!!