Aperture required to see the color of Ring Nebula
Posted 27 January 2018 - 10:32 AM
But, I remember I saw it once in Chabot observatory, through its 36” reflector. That was a lively colorful view, very bright. Those internet photos can’t do it justice. I remember vividly the inner edge of ring was blue, with hue of green, outer edge had much warmer color.
Of course, 4.7” can’t be compared to 36”. Did you see the vivid color in your scope when observing Ring Nebula? What’s the aperture size when you saw color?
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Posted 27 January 2018 - 10:45 AM
Used a superb 22" with Ethos' and never saw color or the central star.
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Posted 27 January 2018 - 11:37 AM
From threads I have followed here on CN, seeing color tends to vary by individual. Some can and some can't. I have never seen color in my C14. Wish I could though
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Posted 27 January 2018 - 11:44 AM
The only color I see on the "Ring" is when I use an OIII or UHC Filter.
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Posted 27 January 2018 - 11:45 AM
As an imager, I'll note that color you see in images is always strongly enhanced/modified in computer processing. As it comes straight from the camera, there's little to see, in a number of regards. _Heavy_ computer processing is as much a part of imaging today as are scopes and cameras. It's just a different thing than visual observing.
Edited by bobzeq25, 27 January 2018 - 11:46 AM.
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Posted 27 January 2018 - 11:46 AM
I've never really seen color (caveat here) with any scope or any eyepiece combination, even as large as a 28-inch. There are others that have seen color with more and less, though I wonder about eating a lot of carrots or averted imagination, a lot of the time.
I've maybe detected the vaguest hint of blue-green once, maybe, but don't remember when, with my 16-inch, or where it was. I've seen the central star with my scope a few times as well, but still no color.
Seeing the central star has nothing to do with seeing color either.
When I did see a hint of color, it was so vague and fleeting it was hardly a confirm, unlike many other planetaries which were like a slap in the face. Many of them are very bright blue, green or blue-green even though the Ring is often so much larger and brighter. Not sure what it is about that.
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Posted 27 January 2018 - 12:36 PM
Certainly the object can show color in 16-18" under good to great conditions, and I suspect considerably smaller scopes might as well:
The key will be to view it as nearly "fully illuminated" as possible: That means the eyepiece used should yield an exit pupil close to or equal to that of the observer. Additional magnification will work against color detection as even fully illuminated M57 is at or just above the "normal" color detection threshold. There are other PNs with higher luminosity that show color better, like the Blue Snowball NGC 7662 in Andromeda, another must see PN.
Regarding the central star in M57, magnification is your friend, up to near the level the seeing will allow. What I do is to back away form the eyepiece slowly until the "space donut" itself is nearly fully masked by the field stop. This is doable and usually will help yield at least glimmers of the central star, or better. A buddy told me that human sensitivity to the deep blue/violet end of the spectrum varies markedly from individual to individual and that is the main reason why some people can perceive it in a 12-16" scope while others struggle with 30". Certainly you need to be dark adapted - one to two hours or even more for your scotopic response to max out your Blue/violet detection threshold. This is understandable due to both the extreme temperature of the white dwarf star, which the optical spectrum climbs steeply into the UV, and the scotopic "purple" response of the eye also, up to four magnitudes at 400-450 nm where the star is optically brightest.
Edited by quazy4quasars, 27 January 2018 - 12:40 PM.
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Posted 27 January 2018 - 05:20 PM
The human visual threshold for color detection is around 18-19 MPSAS. The Ring's SB of ~18 MPSAS therefore puts it just barely into color detection territory. Which suggests one use a large exit pupil so as to not appreciably dim it. For example, a 1 magnitude dimming to 19 MPSAS from 18 results when going from a 6mm exit pupil to 3.8mm.
That the SB is barely high enough to discern color also suggests a large aperture so as to have the object cover a sufficient retinal area--especially given the need for a larger exit pupil. A high SB permits to see color when the object is still small on the retina; stars are a perfect example. But near the color detection threshold an object should subtend probably at least a few degrees. The ~1 arcminute M57 at 200X subtends about 200', or a bit over 3 degrees.
The low SB (from the standpoint of color detection) guarantees that the red component will not be truly seen as other than colorless. Our sensitivity to 650nm light is only 5-10% that for light at 500nm. Any red seen is the result of either illusion or bias borne of familiarity with its photographic aspect. The great visual observers using huge telescopes before the advent of color photography never reported red for other than the very brightest couple or few nebulae exhibiting notable enough of a red component, such as Campbell's Hydrogen Star and the Huyghenian region of M42.
One way to brighten an object is to view it through a sky glow of about equal SB. A sky of SB 18 MPSAS would have the equally bright nebula add to it and so make the nebula appear 2X, or 0.75 magnitude brighter. Of course, contrast is reduced, but double the sky SB is still reasonably good contrast. And the color purity of the emission should have the nebula's hue be not too much 'washed out' by the competing sky glow.
I've looked at M57 through a 24" Cass under a reasonably dark sky and did not discern even a pale green with any certainty; to me it's colorless.
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Posted 27 January 2018 - 05:30 PM
The entire question of viewing distinct colors in celestial objects has to be regarded today as somewhat questionable, especially when various experienced observers disagree markedly in what they see.
While there is no question that color perception can vary to a degree between individuals, some of the claimed colors reported by folks are simply outside the realm of any probability. It should likewise be noted that in the past very few objects were ever reported as showing definite color (outside of a few planetaries and green for the Orion Nebula), regardless of the size of the instrument employed.
I believe that the change largely results from how heavily today's observers are unconciously being influenced by all the over-enhanced images they see on-line, in books and magazine, along with questionable descriptions they read on-line. This can enhance the possibility of their being bias toward seeing color, more-or-less the so-called "averted imagination" effect alluded to upstream. In fact, there is a very real situation called "expectation bias" that we are all susceptible to that I've seen described in the literature in regard to observing situations that is described as follows.
"This is the phenomenon that psychologists call expectation bias, the proclivity of observers or experimenters to allow their expectations to affect the outcome – and the tendency to distort recalled events to make them fit the expectations.”
By example, after reading on CN let's say about how an experienced observer, working from a dark sky site with a big scope, reports seeing some fleeting and very faint feature in an object, someone in a more urban-type setting with a smaller scope is much more liable to go to the eyepiece and honestly believe that he/she can fleetingly see the same thing at their visual threshold. The same is true after looking at highly distorted color images of various deep sky objects, or worse yet, bringing one of those images along to compare against at the eyepiece! This not only applies to faint details, but faint colors as well.
In all honesty, if faint traces of color are truly present in an object they are more likely to be apparent to female observers first, since their color perception is said to be superior to males. While I appreciate that women make up a far lower percentage of observers in this hobby than the males, I still don't see distinct colors being reported by any of the former on CN that I can recall.
Edited by BrooksObs, 27 January 2018 - 05:31 PM.
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Posted 27 January 2018 - 09:04 PM
From my experience viewing M57 with a 17.5-inch viewing the nebula at 380x it often a distinct yellow or yellowish-green with the outer rim reddish. The red sure looks real, but I'm wondering if it is actually some sort of color contrast issue due to the sharp rim and background sky. I do not believe it is due to expectation bias as I don't expect to see red. The central star is often seen, though sometimes with much difficulty - mostly because the glow across the central hole is so strong it makes it hard to pick out.
Edited by StanH, 27 January 2018 - 09:20 PM.
Posted 27 January 2018 - 09:07 PM
For many years I have attended the star parties at Cherry Springs, PA. with the same group of observers. We use 10", 12", 14.5", 17.5" and 20" reflectors. M57 was always generally grey in color except for one night. That night after getting M57 in the eyepiece at the 17.5" I said take a look at this. Everyone saw blue and I did not mention color when I passed on the telescope. Careful inspection of the view through the 14.5" revealed a bluish grey but no where near the definite blue detected in the 17.5".
I find it easier to see color before my eyes become fully dark adapted.
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Posted 27 January 2018 - 09:41 PM
This of course is in stark contrast with the view from my own scope and eyepiece. This is why I asked question about aperture. If you are close to Chabot Space & Science center, probably you can go there and look through that reflector by yourself.
But, we amateurs simply don’t have access to that kind of aperture for our personal telescope, so this question is actually pointless.
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Posted 28 January 2018 - 04:59 AM
It bears repeating that a larger aperture cannot deliver higher surface brightness at given exit pupil (assuming reasonably comparable system transmission efficiency). It merely serves up a larger image, with object and sky having the same surface brightness. (And intrinsic contrast is unchanged, too.) Which is why I highlighted the importance of a larger scope: To present an image which covers a larger area on one's retina. The involvement of more color detectors increases the chance of sensing color.
I'll add that being not fully dark adapted seems to improve color detection. Objects which have sufficient SB to present color--and thus are easily visible with direct vision, at the fovea--do not at all demand dark adaption to any notable degree. After all, dark adaption applies to the non color-sensing rods of the retina. Their improved sensitivity seems to me to somewhat 'swamp' the color-sensing cones. In any event, I find that as the night wears on and my dark adaption deepens, formerly colorful objects become somewhat desaturated in intensity. After a spell under rather bright light in the observatory warm room, upon stepping outside color in the stars and brighter objects is nicely prominent again.
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Posted 28 January 2018 - 03:09 PM
I've looked at it in apertures up to 36" and saw maybe some green.
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Posted 28 January 2018 - 06:16 PM
On the other hand, the only time I've seen obvious color (green) in M57 is when I observed it with a 80mm refractor at very low power (14x).
Posted 28 January 2018 - 09:16 PM
I have seen hints of color as threshold observations in a 15" and I do not think they were expectation bias.It defintely was not just gray like the Pac Man nebula or something.
Posted 28 January 2018 - 11:40 PM
I don't put much faith in my own color perception for DSO's, partially for the reason Glenn mentions: once I have been observing for an hour or more in dark skies I don't see that much color easily. There does seem to be some sort of trade off in color perception as dark adaptation increases. It might take some suppression of the rods/exposure to white light to get a better impression of color and reset the palette. Others describe doing that, but I typically am looking more for lower contrast/finer details rather than color.
And of course color perception is highly individual and relative to what one was most recently looking at. Certainly the use of red LED's has some impact on this, because this is likely to shift our sense of red/orange vs. green and blue. Tying this and the above together I don't see much red to even the reddest stars after I have been at a dark site for some time. Orange is about it, although I do still see color contrst. And when I am ready to pack up and turn on a "red" backpacking LED (which isn't nearly as red as I would like) the impression is of only a pale orange, far whiter than it is early in the evening. My actual astro LED's are true red and do tend to work as a color reference, but they also probably influence my ability to detect redder color for several minutes after use. (This is not because of depletion, since the cones have a very high turnover rate in thousands of times brighter light. But it likely has something to do with the way the brain scales based on perceived color.)
As for the ring, it is bright in the 20" at a dark site after some time observing. I see it and most of the other highest surface brightness planetary nebulae as having that bright bluish-green look characteristic of the class. Fainter ones are grayscale to me. And I see a much bluer/whither tint to the center of M42 typically. The primary DSO's I notice color in other than open star clusters are bright/high surface brightness galaxies and globulars. These have a yellow tint to me.
I don't go looking for color because of its dubious nature and how easily our impression can be manipulated by surroundings, expectations, suggestion, etc. But there is nothing wrong with recording what you see. Just be aware that there is a reasonable probability that the impression is skewed or even incorrect, so don't be overly certain that it is "real." We can only record what we see, and recognize that the impression might not be as real as it appears.
This is similar to star colors. The most clear differences are in double stars, yet the colors there are very much relative to one another. The resultant perceived color can be greatly at odds with a star's spectrum, or even what is possible. And brightness of one to another can also influence the perceived color, with the brighter typically seen as whiter/bluer and the dimmer yellower/redder. Some of this is real some is not...for an example of the real, take a close look at the dimmer pair of Double-double---it has spectral difference not unsurprisingly reflected in the magnitude of the dimmer component, and this can be seen visually.
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Posted 29 January 2018 - 12:51 AM
I've been to fairly dark skies using my C14 ( up to Bortle scale of 2) and cant remember ever seeing color in the Ring. I have friends that say they have seen it but I haven't.
The central star is easier though, at least under dark skies and the ring fairly straight up. The key is magnification, and getting focused on the central area of the ring. Specifically, I can't say how much magnification I had to use but it was above 300x and maybe closer to 400x. The long focal length of my C14 makes those magnifications do-able. I notice once you let enough photons into your eye, it starts to show up. it never is just right there, when i looked for it. Sitting at the eyepiece and just staring into it for a minute makes the difference. Once you see it, it seems to see it again if you look away and then look back at it. Bortle scale of 4 seems to be enough for me to see the central star in my C14, but transparancy has to be very good also.
I've never seen it in my C11 under similar skies.
Edited by aa6ww, 29 January 2018 - 01:12 PM.
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Posted 29 January 2018 - 11:07 AM
My understanding is that for the human eye's color receptors to activate with light from M57, even 16" won't do it.
The problem is our human eyes. A short, 2 minute exposure with an 80mm scope and IMX224 camera does capture the color. Being able to see color is part of why I found EAA so appealing.
Sure, my views of M57 will never match the detail and beauty of a live view through a 36" reflector, but since I'll never observe through one, it makes me happy to know that through EAA I was able to see the colors in M57 (even some of the infrared).
Posted 29 January 2018 - 12:20 PM
Now kindly just wait a minute.
With respect; one can't see infrared "color", we can only see optical colors. infrared frequencies "mapped" to an optically visible color do not count in visual observing. There is a BIG difference between really seeing whats there and seeing what's really not there. I won't go further into the larger issues around visual versus electronically enhanced observing or CCD imaging, here, but I would say, a deep black and white image would be more "honest" then a color-mapped one; and, that's purely my own, albeit reasoned; opinion.
I've seen a subtle blue-cyan Color to M57 almost every time I've looked at it ( once, though, it actually appeared a purplish hue ) in 16" and up, from good sites, over many years. I do think that, with color signal, like almost every other aspect of visual astronomy, the eye-brain connection will -fine-tune itself as a "deep learning" system: what was once disregarded as noise by the brain, may, with multiple viewing experiences, become re-interpreted as useful signal, to a point that probably varies somewhat by individual; or, perhaps fewer cone (color) cells' responses may be required to "alert" the brain to the colors. The brain must "agree" to see what the eye sends it, or it isn't seen.. I also think that the memory of color seen in an object may assist in color detection in that same object later and under different circumstances, as surely as, that we remember we've seen the object before at all. This conjecture reflects my own experience.
We don't fully understand the latent capabilities of the eye/brain system, and that's part of the beauty of visual astronomy. In some degree we are "tuning in" to our own vaster capabilities. It's like cloud-spotting: with time one recognizes subtleties that cannot be described in "ordinary" terms because they aren't seen by "ordinary" sight*.
We certainly are not using our eyes to anywhere the full advantage our early ancestors did; they evolved it for us a s a matter of survival, under sun and stars. We have so many technological crutches.
A final point: How much color do you see by the light of an "average" full moon? And how hard have you tried? How much more do you notice color when the full moon is at perigee, and how much less at apogee? I think we are not well served by "objectively" descriptive system limit models when the reality is that the purportedly described system can or may improve itself in any or all ways, pushing its own so-called limits. OK, thanks,I'm done now.
*sight" in this context is a metaphor for the eye-brain "system"; not just the eye itself.
Edited by quazy4quasars, 29 January 2018 - 02:06 PM.
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Posted 29 January 2018 - 12:33 PM
I also saw M57 through Chabot's 36" scope, and while I could perceive color, it was very, very subtle. It was, to my eye, more like a consistent beige and I couldn't see the gradient that is so obvious in photos. I should have noted the choice of eyepiece to translate that into f ratio.
The Blue Snowball's color is very clear to me at f/10 from urban skies.
Posted 29 January 2018 - 03:57 PM
14" SCT and 20" f/5 Newt., M57 has no color for me, just shades of gray. Very different from the Blue Snowball (lapis lazuli), Eskimo (faint yellow topaz), Spirograph (IC 418, turquoise), Ghost Of Jupiter (aquamarine) and Cat's Eye (blue sapphire).
Posted 29 January 2018 - 04:16 PM
Our ability to see color lies within the cones of our eyes, which are more centrally located and responsible for our daylight vision. This is why we can see color during the day or on very bright objects (like planets) at night.
The rods in our eyes is what gives us a very limited night vision. We can detect faint DSO's using "averted" vision...i.e. - getting the faint light to hit the offset rods of our eyes). We are not nocturnal creatures (astronomers notwithstanding ) and so our night vision has not developed to where the cones of our eyes can pick up much (if any) color at night or when viewing dim DSO's no matter big we make them via magnification. The cones of our eyes cannot detect much beyond subtle blues/greens and perhaps a slight bit of yellow (blue + yellow = green) under low light levels.
This is simply a matter of how our eyes are designed and not a "lack" in our equipment, and aperture will not change how our eyes are designed. Camera sensors however are not designed like our eyes, which is why you see so much more red/yellow in photos that we cannot detect visually only. I'm suspect of anyone who can see red/orange on any DSO. You might "see" it only because you expect it, not because you actually are. The brain is an even more fascinating piece to the optical equation.
We should be quite happy to see those faint fuzzies in any kind of detail, or color beyond gray.
Edited by MarkMittlesteadt, 29 January 2018 - 04:22 PM.