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PostPosted: Sun Mar 02, 2014 3:59 pm 
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Hi folks,

Here's M31 without additional Ha:

    Image

and with some Ha (Hydrogen alpha emission) blended in:

    Image

For your additional viewing pleasure I've made the 4096x4096 pixel versions available here and here respectively. All four images are copyrighted so please do not edit and/or repost without permission.

This is old data from 2012 but it's taken me until now to successfully apply my natural colour workflow (description). The relative RGB values at each pixel have been preserved during stretching with the white balance for the entire image determined by M110. Whether that was a valid white balance choice is for wiser heads than mine. How much prominence to give the Ha data was a matter of personal preference: in the end I chose what I hope is a subtle blend which doesn't overpower the rest of the galaxy and limited the Ha to the spiral structure.

I provided links to the full-sized versions not because they are pixel perfect but because they do offer an ability to see some of the hot blue stars associated with the structure of M31. I hope you enjoy the flight. 8)

Bob.

5 x 1000 seconds in each of R, G and B plus 10 x 1500 seconds Ha. TEC 140 plus ML16803.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
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PostPosted: Sun Mar 02, 2014 10:46 pm 
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Amazing photo, it shows how beautiful galaxy's are and from your description the dedication to shoot it. What are we looking at with the red and blue dots.

Cheers

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PostPosted: Sun Mar 02, 2014 11:29 pm 
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Hi 4xxxx,

I'm happy you like it. It might surprise many that they are stars and those are the correct colours, or at least much closer to the correct colours then you often see. With the naked eye even bright stars are barely bright enough to trigger the eye's colour vision so we are used to seeing them as white dots. Unfortunately that representation has continued with most astrophotography even in the digital age. In order to show the faint stuff the red, green and blue channels are boosted until they tend to max out where star centres are concerned with a consequent loss of colour. The technique I use separates the pixels into three channes but instead of red, green and blue I use HSV: Hue, Saturation and brightness, or V for "value". I stretch the V channel to make the faint stuff brighter and then recombine with the original hue and saturation data to get the result you see, not only for the stars but also for the galaxy disk itself. The only artificial colouring used is for the added glowing clouds of hydrogen gas in the second image.

I hope that makes sense. I must confess I'm on a bit of a crusade on this subject nowadays. I see no good reason to throw away perfectly good colour information where the stars are concerned. It's also true that the same stretching process that loses colour in things like stars can artificially boost colour in extremely faint objects like galaxies, something I've also grown very wary of.

But I wouldn't want to give the impression that this realisation or methodology came easily to me. I look back on some of my efforts from as recently as a year ago and wonder just why I was so pleased with them! If I can help a few others navigate past the pitfalls that trapped me then, IMHO, I'll have achieved something worthwhile.

Bob.

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Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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PostPosted: Mon Mar 03, 2014 6:03 am 
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Wonderful image Bob. Just to check what we're looking at, do I take it that the bright star in the centre is a sun, and the same will be true of what appear to be other galaxies in the same pic?


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PostPosted: Mon Mar 03, 2014 9:41 am 
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Hi warth man,

Thank you. 8)

While there's always a chance that stars in our own galaxy can line up with the centre of other galaxies that's not what we are seeing with Andromeda. It's just that the core of the galaxy is so bright that the light saturated my camera's sensor at the chosen 1,000 second exposure. I could have taken more shots at a shorter exposure time and HDR'ed the set together but it wouldn't have added much if anything in terms of structure.

Galaxy centres are interesting places. Star concentrations are much higher than we see out in the main disk and, unlike the disk which is very thin, stars tend to have more random orbital planes around the centre. And pretty much every large galaxy is thought to host a supermassive black hole at its centre as well - our own galaxy boasts one with a mass of about 4 million times that of our sun. Black holes are, er, black unless they are feeding on other suns or gas clouds at which point they can become exceedingly bright if viewed from the right direction - check out Supermassive Black Holes and Quasars in Wikipedia for more.

Bob.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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PostPosted: Mon Mar 03, 2014 10:13 pm 
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Thanks for the two pieces of information Bob.

Cheers

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PostPosted: Mon Mar 03, 2014 10:15 pm 
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I understand very little of the technicalities you have described, but to just look at those two images, all I can say is 'Wow!" I have looked at them both for several minutes and I can carry on looking…

Simply amazing and I respect the amount of time and effort you have put in to achieving these. It certainly helps to make you appreciate what is up there.

Sarah

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PostPosted: Tue Mar 04, 2014 7:11 pm 
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That's stunning but at the same time haunting when it makes you think how insignificant this planet is in the grand scheme of things.

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PostPosted: Thu Mar 06, 2014 11:21 am 
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Thanks for all the nice comments.

Here's a thought: If you ever see the Andromeda Galaxy with the naked eye or through binoculars (here is how to find it) the chances are you'll see a faint blob which will just be the very brightest parts of the core of the galaxy. It could be quite disappointing unless you know what to expect.

Now step back and think how big our Moon would look in the sky if it were 6 times bigger than it actually is. That is how big the Andromeda Galaxy is in our sky, if only our eyes were sensitive enough. You can fit six full moons along the diagonal from top left to bottom right in the picture above! Now that really would be a Wow. :shock:

Bob.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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PostPosted: Fri Mar 07, 2014 5:28 am 
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That puts it nicely in perspective Bob. Thanks for that. I had no idea about that relative size. The link is useful too, but I note we'll have to wait until the autumn before we can see it again, at least in the northern hemisphere.


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PostPosted: Mon Mar 17, 2014 10:14 pm 
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Stunning images Bob. :shock: and the background information you provide gives a bit of an insight to it all, thanks.

Rorschach wrote:
That's stunning but at the same time haunting when it makes you think how insignificant this planet is in the grand scheme of things.
reminds me of "The Total Perspective Vortex" from The Hitchhiker's Guide to the Galaxy :wink:

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PostPosted: Tue Mar 18, 2014 1:06 pm 
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Hi folks,

I thought I'd have a look at what Hubble had to offer in the small area highlighted in red towards the top left of M31:

    Image

Here's my own stretch of this Hubble data using my normal workflow:

    Image

So many stars (now, where've I heard that before? :wink: ) and when I compared this to my own rendering of the area I definitely got a spot of telescope envy! I was also having difficulty seeing how what Hubble was telling me was actually there could have produced what I saw in my own data. I wondered what would happen if I reduced the scale of the Hubble image to match my own. With the Hubble image registered and reduced in size I added it as a Photoshop layer and then produced a two frame animation to show my own data and Hubble's in sequence:

    Image

The animation is actually at 200% so one can see what is going on a little more clearly and, obviously, I've made no attempt to blend the Hubble star data with the background or to fine tune the white balance. When and where the Hubble data is present all the underlying data from my own image is absent. The match certainly isn't perfect (the star close to the background galaxy in particular :oops: ) but at least I can see how my own small telescope at the bottom of the atmosphere produced what it did. It's amazing what one can see from one's back garden. :lol:

Bob.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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