M16 Eagle Nebula

[Rex]

G'day everyone. this one is from last night. I knew when I started that I only had one and a half hours before this went down behind the neighbours shed, so I did something that I had never tried before, 10min subs. I managed to get in 9 subs and lost two to guiding errors. Hope you like it, as usual critique and advise is very welcome.

Image details:
Object: M16 eagle Nebula
Location: North of Townsville NQLD
Camera: Modded Canon 1100D Astronomic CLS-CCD clip filter
Scope: Carbon Fibre Skywatcher 8" f/4 astrograph, MPCC
Exposure: 7 x 600sec @ ISO800
Guiding: QHY5 4" f/5 newt and PHD
Captured with: APT - Astro Photography Tool
Stacked in DSS and processed in Photoshop CS2

high res version here: http://astrob.in/62064/B/

I have attached a version from before my final colour tweek in PS. At the time I thought it was too red but I will let the public decide. Thanks.

[Larryp]

Looks good, Rex

[Rex]

Thanks Laurie.

[alistairsam]

Hi Rex,

Looks very good, lots of detail in there.
I see you've used the CLS LP filter but with an F4, 10 minute exposures gather a lot of LP even with the best filter and after 4 minutes, there's not much gain in signal. its the brown tinge.
I used to use an 8" F4 and have played around a bit with an IDAS LPS-P2 LP filter. so tested different exposure lengths for the same target and realized that the details in a 10min aren't that different from a 5 minute which is only slightly better than a 3 min.

you can easily remove it with processing software like Startools and PI, attached is a quick wipe in startools.

I'd suggest keeping your subs to 3 to 5 minutes and increasing the number of subs.
That would help reduce LP showing up.

Do experiment if you get the chance.
try 10x3 min exposures and then 6 x 5min and compare. well worth it.
or even single subs.

your guiding and coma correction are perfect.

Cheers
Alistair

[JZ]

Another nice shot Rex. Alistair has some interesting comments!
Interesting to see what startools can do too.
I have certainly learned from this!

Cheers,
Ross...

[Rex]

Thanks Alistiar, some very interesting information. Fortunately for me, the brown in this case comes from my poor processing skills, I think. I only use the CLS-CCD clip filter because where I used to live a couple of years ago I needed it. Where I live now is not perfectly dark but pretty good. M31 is easily visible naked eye, averted vision it is very visible. Thats not to say that LP hasn't played a role in the way this image looked. Just as I finished processing it, I thought it was too red, so I did a selective colour adjustment to change the reds. This is where the orange and brown came from. I have attached the same image to the first post from before I did that final colour adjustment. Please feel free to tell me I am wrong and that you still see LP, as I am really only just starting my astroimaging journey. My processing skills are so good I can make an image look like it is LP affected. :rofl:


Thanks Ross.

[rcheshire]

I like the second image Rex. To me the first is brownish. Great work.

[carlstronomy]

Nice, good to see you are keeping busy Rex, the second image looks great the colours are much more natural.

Carl

[MGTechDVP]

The eagle nebula looks great. You talk about 10 minute subs like its a simple thing... I'm still to get my first 10 min sub thats not trailed.

[Rex]

Thanks Rowland, I have a real problem with knowing when to stop. I am really trying, and comments and advice like Alistair's is exactly what I need to help me sort that sort of thing out. So one day I will know exactly when to stop. ;)


Thanks Carl, I feel like I am improving, just gotta sort out in my own head whats good and whats not. lol.


Thanks Mariusz. I like to live on the edge, and sometimes I get lucky. I really would have no excuse for bad polar alignment as I can see all four of the octans through my polar scope. Impatience is my biggest enemy.

[alistairsam]

Hi Rex,

attached is an attempt at colour wiping your original one.
I've also attached just the gradient that startools detected, imagine this as being overlayed over the data.
that gradient is what has been subtracted from the original.
i'm no startools expert but this is my understanding.

this is an attempt at blinking the corrected one vs. uncorrected. blinking through two or more images is a good way to narrow down what you're final version would be
https://www.dropbox.com/s/yw85vr0qn1acgyz/13.10.29_M16-final_small__2_200k-anim.gif

couple of tips. again, no expert here..

sometimes when you look at an image for too long, you sort of get used to it and you won't be able to pick up that its actually got a color tinge.

if you're using photoshop or gimp and if you want to know if your white balance is correct, you can always use the eyedropper info tool to see what the RGB components of a white star are. just hover it over a white star. that will give you an idea if the white stars actually have a colour tinge. we use this in pre-press where monitors aren't calibrated but the RGB values give us an idea of what the colour is actually like and how it'll turn out when you print it as opposed to seeing it in an uncalibrated monitor.

There are some good images that have been taken from dark sites and that gives you a good reference to see where the nebulosity actually ends in the different areas in your image.
Your F4 actually has captured quite a bit of the nebulosity which is missing in most other images especially at 2 o'clock, so that's good.

i've also attached a crop of a HaLRGB image of the same area. now this will have a lot more detail because he's added Ha details into a colour image but is a good reference to identify where the nebulosity ends and starts in the image. always a good idea to check out the best image you can find and tease out as much as you can from yours. aim is not to see which is better or worse, but to see what you can get out of the image.

this was the source
http://www.nightsky.at/Photo/Neb/M16_HaRGB.jpg

what was the altitude of this when you took it?
I'd suggest avoiding low altitude targets. I once went to a dark site about 160k's away and tried M31 which was about 10deg above horizon. my 7 min subs with a qhy8 turned out brown. so I slewed to a target about 60 deg up, and the background came black. that's when I realized that there was a small town due north of that site and the brown hue was LP glow.
again, this is not a big issue and can easily be removed, but worth remembering.

As mentioned, do experiment with different length exposures and try blinking them to see which is the sweet spot. I'd do this before starting your exposure run as that way you'd get the best use of the clear skies rather than reviewing it at the end.

Cheers
Alistair

[Rex]

Thanks very much for your help Alistair, this is great stuff and I am learning heaps from this exercise. I see there is in fact still a gradient in my image and the one you have corrected looks 10 times better. I will try to find the time to do the tests as you have suggested. Seems a very worthwhile exercise. The one thing I did find with this image, was the noise was so much easier to keep contained than usual, and I didn't touch the saturation at all in the red image, only the orange one, lol. I thought that I was on a winner with 10 minute subs. Oh well we live and learn. Experimentation and great advice from guys like you Alistair is the key to getting better I believe. Thanks again for your help.

[alistairsam]

You're welcome Rex.
Its all about learning and sharing and this is a great place to do it.

Cheers
Alistair

[JZ]

Hi Rex and Alistair,

Fascinating discussion! I'm still learning to drive my gear and haven't got past very short exposures as yet but seeing what you chaps are doing gives me the inspiration to keep going as I can see the results are worth while!
Thanks a lot to both of you for the great info.
I have only just tonight got my guide setup working for the first time and I'm feeling very happy that I have made some progress!

You have shown me something I know I can do too given some perseverance.

Cheers,
Ross...

[Rex]

Hi Ross, as Alistair said sharing and learning is what it's all about. Congrats on getting your guiding going, once you iron out the bugs, you will wonder how you did without it.