The Helix Nebula

[PhotonCollector]

Hi all,

here's my latest image of the Helix Nebula.

Image details

Telescope 12" f/5 reflector telescope, hand guided.
Camera Canon EOS 300D Digital Rebel (not modified).

Exposures:
1 x 3 minute exposures at ISO1600 +
3 x 6 minute exposures at ISO400.
Total Exposure time approx. 21 minutes.

Higher resolution image at
http://www.skylab.com.au/pmsa/Helix%20Nebula.html

NGC 7293 - The Helix Nebula.

The Helix Nebula is a large planetary nebula which spans about the same area of the sky as half the apparent diameter of the Moon. Photographic images of the Helix nebula show the nebula to be even larger, as large as the apparent size as the entire Moon. The nebula owes its large apparent size to its relatively close proximity of just 450 light-years. At about 1.5 light years in diameter the Helix nebula was formed when the central star shed its outer layers into space, stars do this in an attempt to survive, shedding fuel-exhausted layers to re-balance mass and gravity.

Its helical spring-like appearance gives rise to its name the Helix Nebula, a mathematical name for a three dimensional curve that lays on a cylinder or more generally speaking a spiral form. If you examine this image of the Helix Nebula and trace the outer red shapes of the nebula, you may recognise that it appears like two rings joined outlining its cylindrical shape which appears from our perspective to lay on its side and point off to the lower left.

Clear Skies
Paul Mayo

[RB]

Awesome shot Paul.
I had a look at the high res one and it looks stunning.

Nice work.
When did you get clear skies?
:)

[davidpretorius]

this is very nice!

[seeker372011]

Thats an absolutely glorious image. Well done indeed

[ving]

great image!
dispite the fact that i can barely see it from my place its one of my fave objects

[Robby]

Awesome image Paul...!! I have struggled to get a decent image of the Helix recently. Maybe I'll try again.... :D
Cheers

[h0ughy]

That's a nice picture, all the red looking stuff on the right is that due to the amplifier of the canon 300D?

[ving]

interestingly, the helix neb as taken by hubble and altered slightly has been emailed around as "the eye of god nebula"... bit of a false urban legend.
heres some info:
http://www.snopes.com/photos/space/eyeofgod.asp

[robin]

Top shot Paul. Im envious of your focussing skills.

[Striker]

Well done Paul.....I have tried this target and failed....this one is real nice.

[PhotonCollector]

Geeday H0ughy,

That's a very interesting question, one that I have also been asking myself.

No, I don't think it is glow from the amplifier since this imaged is cropped from the original and the original image quite plainly showed the amp. glow on one side of the image in the usual spots.

I think there are two possibilities.

1. it may be red-channel colour-noise produced as a side effect of the image processing I did.

2. it might be extended nebula from the Helix ?

Number 1 would be my first guess. Having said that, it doesn't explain why this "red noise" isn't on the other side of the nebula.

Paul M.

[PhotonCollector]

Thanks Robby,

I've struggled for years to get a decent image of the Helix, so your not alone. Like fisherman, you can't come back with the ultimate catch everytime - to me that's part of the hobby - keep trying and refining your methods, eventually
you'll get there.

Paul M

[PhotonCollector]

Hi Robin,

Thanks.

Nothing worse than spending the whole night imaging only to later find you were a fraction off proper focus. My latest weapon in focusing is to locate brighter stars that have fainter companion stars, like Fomalhaut. I've been focusing on the companion star for a few months now. The tiny companion star is just at the edge of visibility through the camera viewfinder, so it will pop in and out of focus.

Paul M

[atalas]

Nice shot Paul,very interesting colours you have there .

[Itchy]

Hi Paul,

Nice shot of the Helix. A couple of questions though. :confuse3:
Firstly, Are you sure that the red on the right is nebulosity, or is it gradient? I ask because I have seen images of the helix with a red loop on the opposite side, but nothing like what you have on the right.

Secondly, the green in the centre is interesting. Did your subframes show this colour, or is it processing?

Again, great shot. Well Done

[iceman]

Beautiful shot Paul! Very very nice.

[PhotonCollector]

Clear Skies? Ha... Haven't had any for a month now,
but like last night, the clouds seperated long enough
to do 40 minutes worth of PhotonCollecting while
pointed at NGC 300.

Having an observatory certainly gives me the advantage
of being able to "open up" and get imaging within 20 minutes
or so.

Paul M

[PhotonCollector]

Thanks Itchy,

As I mentioned previously I was more convinced it was red-channel noise left over from processing.

Why is the green interesting ? (here's some info about the colours of the Helix I have at hand; look at this AAO Image http://www.aao.gov.au/images/captions/aat015.html it says: "The greenish middle portion is evidence of excited oxygen atoms...." )

By sub-frames do you mean individual exposures ? Thinking that you do, then the answer is yes (otherwise it would not be green in the final image).
However it is certainly my processing which effected the stronger colours.

Do you process 'n stack your images by hand ? or do you have some software that does it for you ?

Best Regards
Paul M

[PhotonCollector]

Gee thanks seeker3702011.

Best Regards
Paul Mayo

[PhotonCollector]

Thanks iceman.

Funny though how the image can look a little ghastly on LCD screens yet look a 100x better on a CRT Monitor.

Paul M

[Itchy]

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OK. It's just that when I did my helix with my 300D, that colour turned out much bluer than yours: (I think you are right about the red noise)

http://users.bigpond.net.au/itchysastro/helix67x30finalweb.jpg




Yes, "subframes" refer to your original individual exposures.


I use ImagePlus to do the basic processing. I shoot in RAW and convert to pre bayer CFA (Colour Filter Array). IP does the calibration (darks, flats and bias) including an auto matched dark. I then covert the CFA frames to colour before I align and stack. IP gives a range of stacking options. With a large number of subframes the sigma average seems to work really well. Once stacked I use IP's digital development process to do the initial stretch and then move to Photoshop to do the levels & curves, etc.

One thing that I have noticed is that ImagesPlus seems to enhance the blue in an image a little more that my manual attempts, so perhaps that is a factor in my centre of the helix being so blue.

Cheers

[PhotonCollector]

Geeday Itchy,

First may I say that is a great image you have of the Helix, really shows the outer nebula well.

Might I also say, that everything else I say might be totally wrong! :-) I'm just a guy who enjoys astronomy and producing images to show other people - so what I say here, is just my humble thoughts.

I think the green colour is lacking in your image because your individual exposures are too short to detect that colour. meaning; there are too few "green photons" to collect in that short exposure time.

My exposures are individually longer (which gives an improved signal to noise ratio than shorter images) and also bear in mind my 'scope collects around 40% more light than yours and at 1/f-stop faster (I think). These factors attribute to collecting a lot more of those green channel photons.

Finally, I will say that most of my raw images also are "too blue" when I first stack them. But I work on the basis that the EOS produces images which have too much blue and therefore you must either add one colour or increase two colours to balance the colour. But this also depends on the amount of sky pollution for that night since pollutions tends to produce more yellow(brown) glows on my images, so the colour handling is slightly different.

BTW: I'm not sure what CFAs or Sigma Averages are. :confuse3: something to do with the auto-stacking software?

PS. Last night I managed 40 minute exposure of NGC300 after that major storm we had (near Newcastle), then it started to cloud in again.

Regards
Paul

[Itchy]

Thanks Paul



You are not alone there Paul!! I've only been doing this (DSLR imaging) for a little over twelve months. There is so much to learn and I think that is what I love about it. Image processing is an art as well as a science and I have learned the most about it by talking to others of like mind. I know that just when I think I have something figured out, I read something that makes me feel as if I know nothing!



You may well be right. I had no Dec drive operational when I took those frames and was limited to 30sec. Also the clouds came in and stopped me taking the extra 40 frames I wanted. I have now sorted my manual guiding and so next time I will increase the sub exposure length. (my scope is 10", f4 BTW)




The CFA (Colour Filter Array) is what the sensor actually records in terms of luminosity. The light passes through an array of coloured filters, one for each pixel, called a Bayer array. So each pixel records only one colour, red, green or blue. To make a colour image, the data has to be "de-bayerised". The three colour values for each pixel are interpolated according to the values of the surrounding pixels.

In astro image processing it is more accurate to perform calibration with dark frames and flat frames before the image is de-bayerised. It is not essential however.

The sigma combine first calculates the mean and standard deviation of each pixel from each frame. Any values outside of one standard deviation are then ignored and the rest are averaged to give the pixel value in the final image. It is good at removing hot pixels that are in slightly different positions relative to the image.



I look forward to your result!

cheers

[tornado33]

Hi Paul.
What I really love about your helix shot is the background galaxies, not just there but actually showing shape :)
Scott