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faackanders2
Carpal Tunnel


Reged: 03/28/11

Re: Color in Orion new [Re: Atl]
      #5537598 - 11/24/12 05:48 PM

Quote:

Is a hydrogen beta worth the purchase? Does it make that big a difference?




I have rarely used my hydroge3n beta filter with my 17.5".
Might have used it more if my Astrocrum filter slide could accomodate 4 filters instead of 3. Definitely get narroband Ultrablock and OIII first, wideband skyglow nezt, before buying H-beta.


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GlennLeDrew
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Re: Color in Orion new [Re: faackanders2]
      #5537694 - 11/24/12 07:01 PM

It's important to realize that no telescope can increase the surface brightness of an extended object beyond that seen by the unaided eye. In fact, because of whatever light losses occur, a telescope always presents an image having somewhat reduced surface brightness, even when the exit pupil is maximal.

Another important fact is that moving closer to an extended object does not increase its surface brightness. If you traveled 100X closer to M42, it would appear 100X larger, but its surface brightness will jot have changed. Yes, due to its now 10,000X greater angular area it will have a *total* brightness 10,000X greater, but again, the surface brightness is no different.

Once an object of given surface brightness has been enlarged enough to perceive color, further increases in aperture, which allow greater magnification for given exit pupil, will not necessarily make the color any easier to see. More detail will be seen of course, but the surface brightness will not increase and so color 'strength' will be the same.

Naturally, the more area an object subtends on the retina, the greater the *total* brightness, which does have a considerable impact. And to some degree, for those threshold objects color wise, a considerable size should help. But if the surface brightness places color detection below human perception, *no amount of aperture whatsoever* can make color magically appear.


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Atl
professor emeritus
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Reged: 04/13/12

Re: Color in Orion new [Re: GlennLeDrew]
      #5537771 - 11/24/12 08:02 PM

That's true, but if that threshold is reached then it can be percieved. Have you got concrete data on what the threshold is for all humans?

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jfaust75
professor emeritus


Reged: 10/04/11

Loc: Central Florida
Re: Color in Orion new [Re: Atl]
      #5537808 - 11/24/12 08:34 PM

So does this mean you can't see color or not? Because I certainly see color in the core(not seeing color in the nebula though)

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jmandell
sage


Reged: 06/15/11

Re: Color in Orion new [Re: jfaust75]
      #5537931 - 11/24/12 10:09 PM

There was one night last year that I saw a hint of pink on the edges with my 12", but it was the best conditions I have ever observed in and I was well dark adapted. I have seen the nebula throught a 25" many times ( from darker skies) but have seen only blue and green.

Congrats on seeing red. It is a truly memorable sight.


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HfxObserver
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Re: Color in Orion new [Re: jmandell]
      #5538058 - 11/24/12 11:44 PM

Having viewed shades of burgundy, white & blue in M42 using a 5-inch refractor the 12-inch reflector a friend has confirms the hints I see. Through a 20-inch even on a mediocre night with Orion just rising these colours are readily apparent.

-Chris


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jfaust75
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Reged: 10/04/11

Loc: Central Florida
Re: Color in Orion new [Re: HfxObserver]
      #5538129 - 11/25/12 12:55 AM

just came in and my memory mustve added to my description....im going with green overall(no blue this time)

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David Knisely
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Reged: 04/19/04

Loc: southeastern Nebraska
Re: Color in Orion new [Re: omahaastro]
      #5538155 - 11/25/12 01:22 AM

Quote:

Although I think we're getting off topic... the original account was of color within IC434 (which personally, I've never seen any hint of).




Neither have I (even in some fairly large apertures). IC 434 is just a little too faint to show much other than the darkness of the Horsehead's inclusion. However, M42 is definitely a different story. Unfiltered, it has always looked a sort of very pale sky bluish to me except for the Huygenian region around the Trapezium and fishes mouth, where the color is dominated by a bluish-green hue. Filtered, the view gets a little more "saturated" with respect to the colors seen. With most narrow-band nebula filters that do not have any secondary passbands, most of M42 that does show color appears as a saturated bluish-green hue. In the OIII filter, the hue is more greenish, but still bluish-green. However, there was one filter where my first experience with "red" became something I would remember for a long time. In the mid to late 1980's, I picked up a Lumicon OIII filter which a friend of mine (astrophotographer Rick Johnson) had recommended I get. We were out observing together one late fall evening when I put my 10 inch on M42. What I saw astounded me, as some of the brighter portions did show a very dim but quite definite reddish hue. I called Rick over and he too saw the red. He put his 10 inch with his OIII on M42, but with his setup, he failed to see that red. We were puzzled until we looked at each of our Lumicon OIII filters with a red light. My filter passed red but Rick's did not. We mentioned this to Jack Marling at Lumicon and he asked for the filters back to make detailed measurements on them. It turns out that mine had a whopping "red leak" secondary passband that Rick's OIII didn't, which kind of explained why I was seeing red and Rick wasn't able to. This kind of convinced me that the red was indeed quite real. I can put my old OIII and my new one that does not have the red secondary passband in a filter switch and actually see the faint reds in M42 appear and then vanish as I switch filters.

Similarly, my DGM Optics NPB narrow-band filter also has a nice big secondary red passband. In my 14 inch f/4.6 Newtonian at around 52x to 79x, the NPB shows some faint pinkish or reddish hues mainly in the brighter regions surrounding the more bluish-green Huygenian area and in the brighter portions of the two "wings" of the nebula. For comparison, I can put in my Orion Ultrablock narrow-band filter or my new Lumicon UHC, both of which do not have any red transmission. With those two filters, there is absolutely no red seen. Some people have trouble seeing the reds in nebulae, and I can fully understand this, as some do not have a lot of red sensitivity at lower light levels with their eyes. However, as for me, my personal "tests" have convinced me that what I am seeing is not an illusion, but real color. Clear skies to you.


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GlennLeDrew
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Re: Color in Orion new [Re: David Knisely]
      #5538552 - 11/25/12 11:21 AM

David's experience with filters on M42 brings up an interesting point. A filter designed to block the majority of light outside a narrow bandpass at the O-III and h-beta lines, but which by accident or design happens to allow the deep red light of H-alpha through as well, can help to better bring out the red in those parts having sufficient surface brightness. But of course, that red which is so visually low in intensity is still having to 'compete' with the quite dominant blue-green emission.

How to eliminate that 'offending' blue-green? Try an H-alpha filter, which is normally used only for imaging. A narrow bandpass type is somewhat better than a dyed cut-off type, as it will more thoroughly eliminate non H-alpha wavelengths. But any deep red filter which passes some 90% or more of the 656nm wavelength will be educational.

Now the challenge is just *seeing* any nebulosity at all. If it appears red, it may or may not be illusory. Because the other, much higher surface brightness wavelengths have been suppressed, the surface brightness of all parts will have been reduced quite remarkably, with only the very brightest part(s) seen at all. Yet to a camera (sensitive to H-alpha), the red is usually the dominant color most everywhere. This exercise will drive home just how awful is the human eye at seeing red.

Try this with other emission nebulae, too. Those having moderate to dim surface brightness, as seen without filtration, through a red filter will not be seen at all. Most certainly IC434! Even when the dominant emission line is H-alpha. In the case of such hydrogen-dominant nebulae as IC434, the California and others, the weaker H-beta line is much more prominent to our eyes. If color were to be seen, it should be at least primarily blue-green, not red.

The surface brightness threshold for color detection is estimated by me as about 19 magnitudes per square arcsecond. But this must certainly vary somewhat with color and its saturation, or 'purity.' Celestial objects are viewed through our atmosphere, which from even pristine locales has its own color from airglow emission. As object surface brightness gets lower, its light becomes dominated by atmospheric light. For example, a reasonably dark sky of surface brightness 21 MPSAS is 3 magnitudes, or 16 times brighter than a nebula such as the North America, which in these conditions can be seen in an unfiltered 10X50 binocular by an experienced observer. Which source do you suppose might provide the stringest color to the view, the nebula itself or the rather brighter sky? And do not forget that the nebula appears brighter than the surrounding sky only because the two sources add together. The nebula's feeble light makes it and the foreground sky together appear to be 6% brighter than the sky itself.


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Meadeball
sage


Reged: 10/22/12

Loc: Midlothian, Virginia
Re: Color in Orion new [Re: GlennLeDrew]
      #5538962 - 11/25/12 03:26 PM

Well, it would seem that if we *are* seeing shades of green (and we can detect the colors passed by a myriad of filters), then our cone cells are indeed operating in dim light conditions. And if they're operating, they're certainly able to detect other colors as well -- provided those wavelengths are strong enough. Personal performance probably varies, so ... ?

I hope y'all aren't treating this as an argument; I'm finding it incredibly interesting. Pity we don't have an opthalmologist astronomer in here!

Meade

Edited by Meadeball (11/25/12 03:27 PM)


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GlennLeDrew
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Re: Color in Orion new [Re: Meadeball]
      #5539047 - 11/25/12 04:25 PM

When different colors are present, the resulting color we see depends on the relative intensity. For any given image point, its color results from an admixture. The more dominant any particular wavelength, the more strongly the perceived color shifts to it. And so what red there is to be seen must 'fight' to get through the much more easily perceived blue-green.

Photographically, the vast majority of emission nebulae are red dominant, but visually the red contributes essentially nothing. One does not find on offer visual H-alpha filters for a good reason; in only a tiny handful of all nebulae (including planetaries, of which Campbell's Hydrogen Star is a standout example) can any red be detected, and mostly with difficulty.

The eye's poor red response, the visual dominance of other colors, the low surface brightness of most nebulae in the first place, and the light of the sky itself all conspire to make visual red detection in all but a few exceptionally bright examples impossible. Bias borne of familiarity with color images must to some extent be operating nowadays, else how to account for the lack of such reports in pre-color photography times, when even meter class and larger instruments were peered into? And knowing the numbers regarding the relative contributions of the light sources involved, and the human visual response, only reinforces this. It's so very easy to color the imagination with a combination of illusion and bias.

The $64 question is: Can the variation in color sensitivity among individuals amount to something of an order of magnitude, or a factor of ten? Specifically, can some enjoy a tenfold increase above the norm in red sensitivity? For that's about what it would take to permit red detection at all near to that claimed.


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Jon Isaacs
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Reged: 06/16/04

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Re: Color in Orion new [Re: GlennLeDrew]
      #5539327 - 11/25/12 07:48 PM

Quote:


The $64 question is: Can the variation in color sensitivity among individuals amount to something of an order of magnitude, or a factor of ten? Specifically, can some enjoy a tenfold increase above the norm in red sensitivity? For that's about what it would take to permit red detection at all near to that claimed.




A few thoughts:

- While informative, I think this thread is beyond the experience and reach a beginner. Any colors detected or perceived in nebulae are subtle at best.

- It is probably worth distinguishing between actually detecting a color and perceiving/seeing that color. The assumption here seems to be that perceiving/see red means that one was detecting a red color... I suggest that the fact that something appears red, particularly in the presence of other other colors, does not mean that it actually is red. The eye-brain is an amazing image processor but it is not fool proof.

Jon


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Meadeball
sage


Reged: 10/22/12

Loc: Midlothian, Virginia
Re: Color in Orion new [Re: Jon Isaacs]
      #5539480 - 11/25/12 10:00 PM

Let me sum everything up to date ...

M42 is FREAKIN' GORGEOUS!!!



Edited by Meadeball (11/25/12 10:01 PM)


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dan_h
Carpal Tunnel


Reged: 12/10/07

Re: Color in Orion new [Re: GlennLeDrew]
      #5539506 - 11/25/12 10:17 PM

Quote:

When different colors are present, the resulting color we see depends on the relative intensity. For any given image point, its color results from an admixture. The more dominant any particular wavelength, the more strongly the perceived color shifts to it. And so what red there is to be seen must 'fight' to get through the much more easily perceived blue-green.

Photographically, the vast majority of emission nebulae are red dominant, but visually the red contributes essentially nothing. One does not find on offer visual H-alpha filters for a good reason; in only a tiny handful of all nebulae (including planetaries, of which Campbell's Hydrogen Star is a standout example) can any red be detected, and mostly with difficulty.

The eye's poor red response, the visual dominance of other colors, the low surface brightness of most nebulae in the first place, and the light of the sky itself all conspire to make visual red detection in all but a few exceptionally bright examples impossible. Bias borne of familiarity with color images must to some extent be operating nowadays, else how to account for the lack of such reports in pre-color photography times, when even meter class and larger instruments were peered into? And knowing the numbers regarding the relative contributions of the light sources involved, and the human visual response, only reinforces this. It's so very easy to color the imagination with a combination of illusion and bias.

The $64 question is: Can the variation in color sensitivity among individuals amount to something of an order of magnitude, or a factor of ten? Specifically, can some enjoy a tenfold increase above the norm in red sensitivity? For that's about what it would take to permit red detection at all near to that claimed.




Once about five years ago I was looking at M42 in late spring and there was very vivid pink coloring around the outer portions. And this was with my 120mm refractor. I have looked at this object many times, often in much larger scopes than mine, and I have never seen any colors other than the often stated blue/green glow in the centre. I was amazed to see the pink when I did. It was as colorful as a photograph.

I have come to believe that what I saw was an atmospheric affect of some sort and did not represent the true color of M42. I am open to other explanations. It sure was pretty and captured my imagination for a number of days.

dan


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Meadeball
sage


Reged: 10/22/12

Loc: Midlothian, Virginia
Re: Color in Orion new [Re: dan_h]
      #5539511 - 11/25/12 10:20 PM

OMG ... it's the CHEMTRAILS!!!!

Edited by Meadeball (11/25/12 10:47 PM)


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Dave Mitsky
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Reged: 04/08/02

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Re: Color in Orion new [Re: Jon Isaacs]
      #5540419 - 11/26/12 02:28 PM

Quote:


A few thoughts:

- While informative, I think this thread is beyond the experience and reach a beginner. Any colors detected or perceived in nebulae are subtle at best.

- It is probably worth distinguishing between actually detecting a color and perceiving/seeing that color. The assumption here seems to be that perceiving/see red means that one was detecting a red color... I suggest that the fact that something appears red, particularly in the presence of other other colors, does not mean that it actually is red. The eye-brain is an amazing image processor but it is not fool proof.

Jon




While I agree in principle with the above, it should be stated that seeing colors, ranging from blue to green, in some of the brighter planetary nebulae such as NGC 3242, NGC 6543, NGC 6572, and NGC 7662 is not at all difficult, particularly through larger apertures. In fact, the nicknames of some of them are indicative of that fact, e.g., the Emerald Nebula and the Blue Snowball. No acquired observing skills are required.

Seeing color in M42 can be a bit harder. It's even more difficult for emission nebulae like M8 but on a couple of occasions I've detected a pale pink hue through 30" plus scopes. I've also seen color in Campbell's Hydrogen Star, IC 418 (the Raspberry Nebula), and Eta Carinae's Homunculus Nebula.

I'm fully aware of the argument about the ability to perceive ruddy hues in M42 as being due to visual contrast effects. What I don't understand, if that's the case, is why the only times that I have been able to do so have been when large apertures were employed at very dark sites under exceptionally good conditions. I typically don't see any color at all in M42 from light-polluted locales, even when using a dome-enclosed 17" telescope.

Dave Mitsky


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Jon Isaacs
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Reged: 06/16/04

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Re: Color in Orion new [Re: Dave Mitsky]
      #5540454 - 11/26/12 02:49 PM

Quote:

I'm fully aware of the argument about the ability to perceive reddish hues in M42 as being due to visual contrast effects. What I don't understand is why the only times that I have been able to do so have been when large apertures were employed at very dark sites under exceptionally good conditions. I typically don't see any color at all in M42 from light-polluted locales, even when using a dome-enclosed 17" telescope.

Dave Mitsky




Dave:

Seeing color in bright planetary's is relatively straightforward. One of my favorites is the NGC 6572, the Blue Racketball which looks green to me. I suspect that a bit of light pollution actually helps seeing color, the greenest I have seen it was from a typically dark site but with at least the first quarter moon.

The red I see in M42 does take dark skies and a reasonable sized telescope... But I suspect that I am not actually detecting red photons but rather some complimentary eye/brain effect.

Jon


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Dave Mitsky
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Re: Color in Orion new [Re: Jon Isaacs]
      #5540546 - 11/26/12 03:42 PM

Jon,

A careful reading of my first paragraph reveals that I said the same thing. It's important for beginners to know that some deep-sky objects do indeed exhibit color. As far as NGC 6572 is concerned, I prefer the nickname the Emerald Nebula.

Can anyone explain then why this eye/brain effect only seems to happen under certain conditions?

Dave Mitsky


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cadfour
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Reged: 07/26/12

Loc: Melbourne, Florida
Re: Color in Orion new [Re: omahaastro]
      #5540687 - 11/26/12 05:18 PM

I observed M42 (Orion Nebula) on Saturday. I saw blue..with a hint of green....am I the crazy one?

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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Color in Orion new [Re: cadfour]
      #5544069 - 11/28/12 03:20 PM

There are two issues at play, with M42:
1) lab studies show that when 2 gray squares, illuminated to *barely* the limit of scotopic vision, but one a tiny bit brighter than the other, are presented to the observer, we all see the fainter one as "reddish" or "pinkish" and the brighter one as "greenish". This alone says we should trust our eyes very little when used at or near the limits of vision, if color is seen.
That we all see it is NOT a sign the color is there, merely that all of us have eyes that work the same way.

2) when observing M42 (and heaven knows I've looked at this nebula with 2" to 60" aperture at least a thousand times over the years), sometimes more colors than simply greenish-gray or pinkish-gray present themselves.
It seems that, on those nights, the nebula is SO bright in the telescope that a quick glance away from the scope shows that night vision has been damaged.
And the range of colors seen extends to yellowish-beige, bluish, pinkish, purplish, reddish, mauves, and simple grays, and nearby NGC1977 appears quite blue. One such night, I drew a simple map of the nebula, indicating where I saw each color, and compared it to a color photograph of the nebula, and found I had correctly indicated where each shade was found. So I am certain that, under the right conditions, colors can be seen in the Orion nebula. My vision at the time was probably mesopic, and not purely scotopic.

3) But these colors are not ALWAYS visible. As an experiment, I tried viewing the nebula through an H-alpha filter. Only the brighter sections could be seen, and the brightest part, even in H-a, was the central region.
When using a filter that transmits H-b and O-III, the entire nebula can be seen. That's not surprising since every nebula that emits H-a also emits H-b at a lower level, and because our peak sensitivity at night hovers around 500nm (near the H-b wavelength).

4) Recently, I've had a chance to compare narrowband filters that have substantial transmission at H-alpha with those that have zero transmission shorter than 700nm.
It may very well be that the restriction of bandwidth creates a greater ability to see the reddish colors than a non-filtered view, because the non-filtered view didn't present them as strongly. Or that the diminishment in brightness of the entire field resulted in that red/green illusion at the limit. How to tell?
It appears the reds I am used to seeing must be real, because they are visible in the filters WITH H-a transmission, but disappear with the filters that do not have H-a transmission.

5) Different observers have different sensitivities to colors, but it seems that on the nights where I see many colors, or very strong colors, so does everyone else in the observing site, and with a wide variety of apertures. I did not record particulars about the observations, but a memory search recalls that these were nights of exceptional transparency (very low extinction) and darkness.

So what can you say about the visibility of colors in M42/M43/NGC1977?
--it varies from person to person
--it varies from night to night
--it varies according to the filter used
--it varies by aperture (the reds were stronger in larger aperture)
--if "at the limit", the colors may not be real.

But if you have a night where you can see ANY tint to the fainter interior of the nebula, looks at those sections on either side of the central region and see if one side appears yellower than the other. If you see that, I believe you are seeing REAL colors in the nebula. Just don't expect to see them all the time.


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