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Minimum Aperture to detect color from DSO

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#1 shkong

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Posted 06 March 2013 - 04:37 AM

I had good view of Orion with good degree of nebulosity with 12 inch Zhummel Dob.

But I could not notice any color on it.

What is the minimum aperture to see the color from DSO?

Do I need some filters to enhance the color?

Thank you in advance

Thomas :cool: :question:

#2 David Knisely

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Posted 06 March 2013 - 05:29 AM

Seeing color in deep-sky objects is mostly a function of the sensitivity of the eye of the observer rather than just being a function of aperture. While some color can be observed in some of the brighter emission nebulae, most show little color because the eye just isn't sensitive enough to pick it up. In the case of the Orion Nebula, at lower powers, I can see a pale bluish or bluish-green coloration in the brightest portions of the nebula when using eight to 10 inch apertures. However, the color tends to be rather weak. In the case of some of the smaller brighter planetary nebulae, the bluish-green color is a little more intense. However, in most other deep-sky objects, people usually see very little in the way of color at all. I can see some faint reds in M42 using my DGM Optics NPB filter in a 14 inch telescope at fairly low powers (59x to 135x), but they are pretty weak compared to the bluish-green of the core region. However, some people won't see any color at all regardless of how big their telescope is simply because their eyes aren't sensitive to color at the low light levels we have to deal with. Some people see the color while others do not. Try using fairly low powers in your telescope and stare at the brighter regions to see if you can glimpse a little of the bluish-green color M42 has. Clear skies to you.

#3 sg6

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Posted 06 March 2013 - 06:44 AM

For Orion I have read of people saying 14" and others saying 16", sorry you seem to just miss it.

However any mention is referred to as hints of colour, not it was in glorious technicolour.

Your eyes make a difference, a kid of 10 or 12 may well see colour through your 12" in Orion. If they do and keep telling you they can see colour you are allowed to strangle them slowly. :lol: :lol: Maybe stop when they turn blue.

I would assume that also as we are talking very low levels of colour that the general light pollution whereever you are is also a contributing factor, as always the darker the skies the better for greater contrast.

#4 JakobKS

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Posted 06 March 2013 - 06:57 AM

For Orion I have read of people saying 14" and others saying 16", sorry you seem to just miss it.

However any mention is referred to as hints of colour, not it was in glorious technicolour.

Your eyes make a difference, a kid of 10 or 12 may well see colour through your 12" in Orion. If they do and keep telling you they can see colour you are allowed to strangle them slowly. :lol: :lol: Maybe stop when they turn blue.

I would assume that also as we are talking very low levels of colour that the general light pollution whereever you are is also a contributing factor, as always the darker the skies the better for greater contrast.


Assuming you can see when they turn blue... :lol:

#5 Jon Isaacs

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Posted 06 March 2013 - 07:51 AM

I had good view of Orion with good degree of nebulosity with 12 inch Zhummel Dob.

But I could not notice any color on it.

What is the minimum aperture to see the color from DSO?

Do I need some filters to enhance the color?

Thank you in advance

Thomas :cool: :question:


Thomas:

First let me say hello and welcome to Cloudy Nights.. :whee:

Second:

I found this post by Don Pensack particularly useful:

Seeing Color in Deep Sky Objects

I often see faint tints of green and fainter tints of red in M42 in a larger scope, I see it in my 12.5 inch. And I see it in a smaller scope (4 inch) if things are right. But Don's point suggests the this is probably an artifact of my vision.

Jon

#6 Tony Flanders

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Posted 06 March 2013 - 08:22 AM

I had good view of Orion with good degree of nebulosity with 12 inch Zhummel Dob.

But I could not notice any color on it.

What is the minimum aperture to see the color from DSO?


This subject comes up frequently, most recently in the Deep-Sky Forum in this thread. We really ought to have a FAQ on it.

In my opinion, if you don't see color in M42 through a 12-inch scope, you probably won't see it in any scope. I see the inner parts of this nebula as faintly green even in 4-inch scopes.

Going beyond that specific question, though, here are the salient points of the answer:
  • Deep-sky observing is not about color; it's basically done in black and white. Or perhaps more accurately, black and gray, or black and off-black.
  • Few or no celestial objects have genuinely vivid colors; probably the ones that come closest are carbon stars. Double stars often have interesting color contrasts, but they're subtle. Colors on planets can be gorgeous, but they're very very subtle -- delicate pastels.
  • Filters impart their own color to a scene; therefore, they always detract from the natural colors and can never enhance them.
  • Color perception varies hugely from one person to another, and it's difficult or impossible to tell which of the colors that people perceive are "real" and which are illusory.
  • Of all non-stellar deep-sky objects, the only ones that appear significantly colored to most people are a very, very small number of emission nebulae, notably the inner regions of M42, and a somewhat large number of small, intense planetary nebulae such as NGC 7662, the "Blue Snowball" in Andromeda.


#7 JIMZ7

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Posted 06 March 2013 - 08:22 AM

In my 10" f/5.6 Dob M-42 is light lime green in color at 54x & 135x using Plossls. About 25 years ago using a superb Coulter 8" f/6.9 reflector M-42 also showed light green but also some red mixed in using U.O.Konigs & Televue 11mm type-1 Nagler. This is in the "white zone" area of Metro Detroit.

Jim :dob:

#8 shkong

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Posted 06 March 2013 - 08:40 AM

Thanks a lot for your valuable opions.

It may vary on each person.

#9 shkong

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Posted 06 March 2013 - 08:41 AM

I will try again in the clear sky.

#10 shkong

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Posted 06 March 2013 - 08:44 AM

The connected post by Don is very interesting.

Thanks

#11 shkong

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Posted 06 March 2013 - 08:46 AM

Very helpful opinion.

I agree with your conclusion.

Thanks Tony

#12 isawit

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Posted 06 March 2013 - 08:55 AM

I was out viewing several nights ago with my 10X50 binoculars and could see a faint greenish glow in the Orion nebula. I had tried my cheap and old 60mm refractor before switching to the binoculars and couldn't see any color. It was a clear night for viewing and I live in a gray area.

#13 George Methvin

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Posted 06 March 2013 - 01:35 PM

Best color I ever saw in M-42 was many years ago very early one cold morning. I was viewing through a Coulter 13.1 inch dob the reds and blue-green color just jump out in the nebule, the eyepeice I was using was a meade RG 20mm eyepeice at that time. I have never sence then seen that much color again in M-42 even through a 17 inch dob I owned for a while. I will never forget that morning.

#14 Allan...

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Posted 06 March 2013 - 01:59 PM

My eyes (60 years young) do not detect any color in M42 (8" dob) yet my son who is 25 CAN see greenish color in it (through my scope). Guess I started this hobby a bit late...but thats life..lol.

#15 George Methvin

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Posted 06 March 2013 - 02:30 PM

I was around 32 year old when I view M42 that morning many years ago now at 61 I really don,t see any color in M42 with my 10 SCT....sad really, but I will alway have that morning and that wonderful color view of M42 in my minds eye.

#16 GOLGO13

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Posted 06 March 2013 - 05:13 PM

i see color in the blue snowball and some other planetary nebulas even in a 4 inch refractor. my 10 inch shows greenish on m42. use low power if you are in light pollution. star color can be in any scope...aperture can help...and good optics

#17 GlennLeDrew

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Posted 06 March 2013 - 05:50 PM

Aperture by itself is important only so as to sufficiently magnify smaller objects to an apparent size the eye can resolve. For larger objects (such as M42), a smaller scope suffices to detect color. The smaller the object, the more aperture is required; halve the object diameter, and double the aperture needed. No matter the aperture, the view can only be as bright as seen by the eye alone (and then only when the exit pupil is as large as the eye's iris). It's important to realize that for extended objects like nebulae and galaxies, the image surface brightness at given exit pupil diameter is always the same, no matter the aperture. A larger aperture only allows to see smaller objects and finer details; it does not increase surface brightness nor contrast.

The brightest nebulae have a surface brightness of 14-15 magnitudes per square arcsecond. The color detection threshold is perhaps 18 MPSAS. And so those few nebulae (almost all planetaries) for which color can be seen are only 3-4 magnitudes brighter than this threshold.

Image surface brightness scales as the area if the exit pupil. If you increase magnification by 58% (e.g., going from 100X to 158X), the view will become 1 magnitude, or 2.5X dimmer. Over the range of exit pupils commonly used, namely 7mm down to 1mm, image surface brightness gets 49X, or 4.2 magnitudes dimmer.

We see that small exit pupils can render even the brightest nebulae colorless. For the best chance at seeing color, use lower powers, unless the object is tiny and needs *some* magnification boost to enlarge it sufficiently so that the eye has at least some size to work with.

#18 Jon Isaacs

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Posted 06 March 2013 - 08:02 PM

We see that small exit pupils can render even the brightest nebulae colorless. For the best chance at seeing color, use lower powers, unless the object is tiny and needs *some* magnification boost to enlarge it sufficiently so that the eye has at least some size to work with.



Glenn:

I do find that there are situations when color is quite apparent and other times when the conditions, exit pupils, magnifications are essentially identical, an object appears colorless. For me, the Blue Racketball, NGC6572, (13.6 magnitudes/square arcsecond) sometimes is bright green, sometimes it's not.

I attribute this to difference to some unquantified difference in the dark adaptation of my eye. Full dark adaptation does not seem desirable.

Jon

#19 GlennLeDrew

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Posted 06 March 2013 - 10:06 PM

Jon,
You raise an interesting point which accords with my own experience. Objects bright enough in which to detect color necessarily elicit a response in the retina's cones, which do not require dark adaption to function. I've found that after some time in the dark, colors become somewhat de-saturated, or less intense, even though I can see to fainter limits. Exposure to some amount of white light, sufficient to impair dark adaption to a good extent, helps to bring back the perception of richer hues in the colorful nebulae (and stars, too.)

#20 GOLGO13

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Posted 06 March 2013 - 10:18 PM

I think I have also noticed this. The more dark adapt I get the less distinct the colors are. Depends on the object though. Larger aperture can help in some cases. For instance, the blue snowball is blue at low powers in my 10 inch. But at high power it's more grey. But, in my friend's 16 inch at high power it was still blue (fairly dark site and fully dark adapted). And in a 30 inch scope planetary nebulas can really start to look cool.

#21 GlennLeDrew

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Posted 06 March 2013 - 10:27 PM

Indeed, at given surface brightness, the more area an object occupies on the retina the better seen is the color.

#22 GeneT

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Posted 06 March 2013 - 10:31 PM

Seeing color in deep-sky objects is mostly a function of the sensitivity of the eye of the observer rather than just being a function of aperture.


This is true. Years ago, telescope companies overstated the amount of color one could see as they moved up in aperture in their line of telescopes. Also, most people are color blind to some degree. Lastly, different eyepieces, and glasses (if worn) will also affect the color of sky objects.

#23 shkong

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Posted 06 March 2013 - 10:35 PM

Thanks Glenn for your detailed analysis.

I had read an article that compare the visual view of M42 through 30 inch Dob and 8 inch AP refractor,

It claimed that although 8inch AP refractor shows clear 3-D separation of stars in nebulae, 30 inch Dob shows more splendid visual color in the dark sky.

In the future I would like to experience view through good 16 inch myself.

Thomas

#24 Astrodj

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Posted 07 March 2013 - 02:20 AM

Seeing color in deep-sky objects is mostly a function of the sensitivity of the eye of the observer rather than just being a function of aperture. While some color can be observed in some of the brighter emission nebulae, most show little color because the eye just isn't sensitive enough to pick it up. In the case of the Orion Nebula, at lower powers, I can see a pale bluish or bluish-green coloration in the brightest portions of the nebula when using eight to 10 inch apertures. However, the color tends to be rather weak. In the case of some of the smaller brighter planetary nebulae, the bluish-green color is a little more intense. However, in most other deep-sky objects, people usually see very little in the way of color at all. I can see some faint reds in M42 using my DGM Optics NPB filter in a 14 inch telescope at fairly low powers (59x to 135x), but they are pretty weak compared to the bluish-green of the core region. However, some people won't see any color at all regardless of how big their telescope is simply because their eyes aren't sensitive to color at the low light levels we have to deal with. Some people see the color while others do not. Try using fairly low powers in your telescope and stare at the brighter regions to see if you can glimpse a little of the bluish-green color M42 has. Clear skies to you.


If it is not too time consuming for you, could you illustrate where in the nebula you detected red tinges? I have always been able to easily see the green and bluish coloration of M42 in scopes as small 8" (indeed, I can see the greenish parts in much smaller apertures), but pink or red hues have eluded me. It could be I have not observed carefully enough in the right areas.

Any help would be greatly appreciated. I will heed Jon, Glen's, and Golgo's comments on dark adaptation being a possible hindrance as well.

Thanks!

#25 GlennLeDrew

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Posted 07 March 2013 - 02:55 AM

I have managed to glimpse the subtlest of a red tinge near the 'heart' of M42 using an unfiltered 16" Newt at low power. It was indefinite enough to make me wonder if illusion or expectation might not have contributed.

I have some doubts about this having been a real detection of red because I know just how poor is the eye's response to H-alpha emission at 656nm. The O-III and contributing H-beta emission, near 500nm, are close to the eye's peak response, and so will dominate. The red H-alpha must 'compete' with the visually much brighter (bluish-) green, rendering it as largely 'washed out.'

Moreover, if H-alpha is of sufficient intensity to be seen as red, whether admixed with other nebular light or not, it should be expected to be at least slightly detectable--as colorless even--when an H-alpha filter is brought to bear. I've not tried it yet myself, but at least one other observer has done this and reports seeing some nebulosity in the inner, brightest part of M42; red or colorless, I cannot recall. But my impression is that this light was very dim to be sure, which further inspires doubt in me as to the red being of sufficient brightness to be detectable as such through the much brighter veil of dominating green.






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