Thanks Guys, The way I think about it is this. As Joe stated, our eyes are not so great at picking up deep space objects because of the way they are designed. The colors coming off of these objects are fairly consistent. As we all know when night falls, our cones turn off and rods turn on...rods are good with black and white, and movement, but not color. When I stare at M42 for a minute or two, I can make out some reds and blues as my cones start to turn back on because the object is so bright, even with my 10" OTA. The CMOS sensor is not inventing any new colors for these objects, it is simply designed to pick up wavelengths of the electromagnetic spectrum from around the start of UV light, into Infrared light. The CMOS is naturally good at detecting IR light, and has to have a filter put in front of it to block that light for your average end user photographer (I removed this filter to make the camera shoot IR again). You can tweak them a lot, but for the most part, each gas is going to give off its signature light wavelength in the electromagnetic spectrum. Just because we cant see it with our eyes doesn't mean that is not the real color. I think the camera is doing a much better job than our eyes of seeing and capturing the color. Another big problem with our eyes is how small they are. The average pupil can open to about 7mm, this is not a lot of light capture to start with. A 9.25 inch mirror equates to about 1126 eyeballs worth of light gathering power. On top of that, our brain is refreshing our vision at around 30Hz, so our photon capture is being refreshed/drained very fast. A camera does not have this problem, it can just keep collecting photons as long as you leave it open. When you shoot an primarily Ha Nebula, it is always red, that is because the excited hydrogen is giving off light just off the red side of visible light in the infrared range, when you shoot a reflection nebula, it is blue, that is because light tends to scatter in the blue wavelength, and not in the red. Our sky is blue for the same reason that reflection nebulae come out blue. I guess my main point is this, the colors are accurate, the instruments are just better at capturing them than our puny little eyeballs. Even when you get a "false color" image, it is usually just a compilation of the selective shooting of each gas, as each gas will give off light in a different wavelength, so in reality, its not really false color, its selective color. I've heard that if you represented the electromagnetic spectrum as a film strip that went up the west coast of the USA, what we see with our eyes, visible light, would take up just one frame out of that film. O.o Anyway, I thought I would share some thoughts on this. If I made any mistakes, please point them out. Always like to learn more about this stuff. David Rankin Joe Bauman wrote:
Color in space is a topic that has puzzled me too. (We can get philosophical and wonder if one person perceives vision itself the same as another, which is challenging to think about.) Concerning color photos of deep-space objects, I think the reproductions do have some validity. That is, if five astrophotographers using the same filters and exposures compare their work, they would be similar. There is a basis for the color, some objective reality in space. The tints are not the same as we can see with our eyes because our eyes are highly limited instruments, needing a certain intensity of light to see color at all. And there are plenty of electromagnetic wavelengths out eyes can't perceive at all. When CCD cameras gather light over long periods, they are improved versions of our eyes, accumulating and multiplying the photons, so they recognize color in dim objects we could never detect without such help. But the colors really are there in the sense that we can record them. Probably actual wavelengths of colored objects in space could be measured to give particular tints and shades.
But I'm also sure there is a big component of art involved in making astrophotos. We need to take into account such things as how much the atmosphere distorts the colors, making the problem awfully complicated.
That's just my opinion and maybe others in the group could improve my understanding.
-- Thanks, Joe
--- On Tue, 12/1/09, Chuck Hards <chuck.hards@gmail.com> wrote:
From: Chuck Hards <chuck.hards@gmail.com> Subject: Re: [Utah-astronomy] M51 reprocessed To: "Utah Astronomy" <utah-astronomy@mailman.xmission.com> Date: Tuesday, December 1, 2009, 11:23 PM
Don't beat yourself up, David. Saturated colors in astronomical images are all fake. We try to approach what the various objects might look like if they were actually bright enough to trigger the color receptors in our eyes, but all deep-sky astronomical images are really just art, when it comes right down to it. An article in S&T some years ago (and even a "Sky-Wise" cartoon by Jay Ryan) demonstrated that even if we were much closer to these galaxies than we are, they would look about like the Milky Way looks to the naked eye from a dark site. Impressive, yes, but not tinted blue and red. Even if we were immersed in the Orion Nebula, the brightest parts would appear as a colorless, grey vapor instead of the red we are used to in photographs, or are on the verge of detecting visually in large aperture scopes. The colors are thanks to our insturmentation. The challenge in astro-imaging is to pursue ever smaller star images- crisp, tight focus. Diffraction-limited imagery. The colors are just what pleases the eye.
This one does match what we are used to seeing much more closely. Keep up the good work!
On Tue, Dec 1, 2009 at 6:52 PM, David Rankin <David@rankinstudio.com> wrote:
I didn't realize how bad the processing on my M51 shot was until I got home. I started over on a real monitor, and here is the new result. I had way over saturated the reds before.
http://www.slas.us/gallery2/main.php?g2_itemId=2718&g2_imageViewsIndex=1
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