Rho Ophiuchi

[archioptic (Nathan)]

Hey guys, looking for some help on imaging this one. I'm finding it difficult to capture the darkness of the cloud since I cannot get enough contrast with the background. Besides imaging from a darker location, stopping the lens down to get better focus and collecting more data, is there anything I can do to improve this?

Nikon D3100 & Nikkor 180mm ED AI-S @ f2.8
10x120" @ ISO1600
Mounted on an NEQ6 pro w/ autoguiding

[raymo]

Firstly Nathan, if your NEQ6 is decently aligned, you don't need to waste your time autoguiding at a focal length of 180mm. Your mount will give
you round stars for at least 5mins at that focal length. I image unguided
for 120 secs at 1000mmm. f/l.
Secondly, if light pollution allows it at your location, go for longer subs, and more of them.
raymo

[archioptic (Nathan)]

Thanks Raymo. I definitely agree with the autoguiding comment. I hadn't had a chance to use it before, so I was mostly just figuring out how to get it going for when I set the ED100 up next. I'm thinking a darker site might be the way to go for this one.

[LightningNZ (Cam)]

Rho is one of those targets that needs a huge amount of time - and the more the merrier. I've never tried capturing it as I've never had an appropriate focal length to tackle it, but you should seriously consider hammering it for at least an hour, if not two.

[MrB (Simon)]

As Cam says, The longer you can go on Rho the better.
I shot Rho from a very dark site recently, did 5 min unguided at f4 and iso 1600 but I wish I had taken them at 800 for 15 mins guided.
Very rough process attached, I went a bit soft on the saturation.
I'm going to revisit this one next season, eventually I'll be happy with it.

[archioptic (Nathan)]

Thanks Simon, great shot! A darker site is definitely the way to go it seems. It's starting to set early now so might have to wait til next season.

[MrB (Simon)]

Thanks Nathan, it looks okay at that scale, but at 100% there are lots of issues and I'm really not happy with it. I took 5 hours of subs that night :/

Originally Posted by archioptic

A darker site is definitely the way to go it seems.

Definitely. From home my exposures at 1600 and f4 are sky limited after about 1.5 to 2 mins.
Attached is an example of a single 5 min sub from the previous image, compared to a stack of 2 min subs from home. Same equipment and settings, only the exposure length changed. The difference is huge. These were only stretched, so the light polution gradients are still evident in the bottom image.
The 5 min sub was no where near sky limited, I was only limited by my polar alignment, with guiding I could have gone much deeper.

[archioptic (Nathan)]

Simon, that's exactly the example I needed to see I think. Definitely makes it clear how much I was limited by the light pollution. 2 minutes at 1600/f2.8 left me with an almost overexposed image. I'm pretty lucky that I can reach some fairly dark sites nearby so I might give it a go before it sets too low.