Iris Nebula advice please

[jnc71106]

Ok I'm planning on shooting the Iris nebula in the next week or so

Would just like some advice on sub length etc

I've got a 80mm triplet that will be at F/4.8 an atik 314l, LRGB + HA OIII SII filters and pretty dark skies

What length subs should I be going for and should I be using LRGB or HA+RGB

Cheers all

[AndyUK]

Well, the centre of the Iris is a reflection nebula, and of course the outer area is the dark nebula - I think you'd be wasting your time bringing an Ha filter to the party

With regards to LRGB exposure times, I had a crack at this myself with my reduced Equinox 80 (f5) and 314L+ about 3-4 weeks ago (WIP here), but I really couldn't say that it was a dark site at all! I got the L exposure totally wrong - 900s totally blew out the centre of the Iris and gave me real problems when processing - If I were taking the L again I'd try 420s next time, but in order to try and tease out the detail in the dark nebula, I'd want to get a LOT of them.

Regarding RGB exposures, My personal "default" at the moment is 240s as anything longer seems to start to blow any colour away, but as you can see from my effort, there's an awful lot of noise in there so I know I'm going to need at least another couple of nights on this to capture anywhere enough data...

Good luck, and I look forward to seeing how yours comes out. If you find you're a bit short on data, drop me a PM and you can have a copy of mine to play with

(Hope that helps?)

[jnc71106]

thanks very much andy. do you bin your rgb ??

[AndyUK]

Not with the Equinox 80, no. My reasoning may well be totally flawed, but it's to do with my gut feelings on resolution - Unbinned I get 3.32 arcseconds/pixel, which means when binned it doubles to 6.64, which is a bit too low for my personal liking!

Even though I know the RGB is only really there for colour, I prefer to image unbinned at this resolution as it also then gives me the opportunity of adding all the RGB subs in with the Luminance... (or even not taking any Luminance at all, but if I feel like it, I can then create a "false" Luminance from them...)

[jnc71106]

thanks once again andy looks like a target for doing over a few nights. yours looks great and gives me something to aim for at least

[ollypenrice]

What you can do, and it works very well in these situations, is let the core blow out big time in the Luminance channel. Apply it fully to the RGB, then paste the LRGB onto the RGB-only and let the RGB-only core through by gently erasing the over exposed LRGB. Areas of very strong signal, like Alnitak in Horse images, are often best controlled just in the RGB layer. You don't lose resolution because the signal is so strong that it will take enthusiastic sharpening.

http://ollypenrice.smugmug.com/Other/Nebulae-and-clusters/i-K7znZCh/0/X3/IRIS-12-HOURSLM3-X3.jpg

Olly

[AndyUK]

Cheers Olly - Thanks for that tip! I'll have to have another go at processing mine (it looks as though we're going to have plenty of "re-processing" time until the next clear sky comes along )

[ollypenrice]

Cheers Olly - Thanks for that tip! I'll have to have another go at processing mine (it looks as though we're going to have plenty of "re-processing" time until the next clear sky comes along )

Same here!! It's lousy.

Olly

[Gina]

Dreadful here too. We have had a least some rain every day sine this area was announced as being in drought!! Very heavy rain most of today and it's still raining a bit. It's supposed to clear up later, ha ha!

[ollypenrice]

Probably good for the irises?? Tim's yer man to answer that one.

Olly