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Observing >> Deep Sky Observing

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azure1961p
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How much aperture for technicolor?
      #5697971 - 02/24/13 10:02 AM

I get that we use skotopic vision in deepsky visual observing for the most part and that our retina/brain in low light is part of the reason we see blue, green and greys. Is it ever possible though to have aperture large enough m42 or even the horse head vividly shows those deep crimsons and such. I've seen top artists produce deepsky drawings through huge observatory aperture but always shades of grey. The upshot of it all is, how big a mirror do you need to finally collect enough light to equal the CCD and photo images?

I'm guessing its impossible and that the contrasts and such are too skewed artificially to ever reveal the like even through a mirror miles across. Another limitation would seem to be image scale and exit pupil. If here were such a thing as a 10,000 foot aperture the magnification even with huge oculars custom made would be gargantuan and that not to say you could even see all the exit pupil.

It would seem, unless I've got it wrong there is a cap on aperture for say, a 150x view of M51.

Thanks in advance.

Pete


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Tony Flanders
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Re: How much aperture for technicolor? new [Re: azure1961p]
      #5698001 - 02/24/13 10:25 AM

Quote:

Is it ever possible though to have aperture large enough m42 or even the horse head vividly shows those deep crimsons and such.




Absolutely not. The intensity of light coming from most of M42 is too low to stimulate color vision -- period. A telescope can only make the intensity lower, not higher.

Quote:

The upshot of it all is, how big a mirror do you need to finally collect enough light to equal the CCD and photo images?




That's not the right way of looking at this question. CCDs and human eyes see things differently. CCDs will always see more details in faint objects. Which one is better or more aesthetically pleasing is a matter of preference.

Quote:

It would seem, unless I've got it wrong there is a cap on aperture for say, a 150x view of M51.




Right. You will get no gain from a telescope producing an exit pupil larger than your eye's pupil. Taking 7 mm as a taking human pupil, that means that the maximum useful aperture for 150X is 150 x 7 mm = 1050 mm -- still within the range of (very large) backyard telescopes.


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IVM
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Reged: 01/07/08

Loc: Western New York
Re: How much aperture for technicolor? new [Re: azure1961p]
      #5698009 - 02/24/13 10:31 AM

I read a report from the first light of the Japanese telescope atop Mauna Kea (8.5 meters?) with an eyepiece specially made for the occasion, and an observatory worker claimed that the visual views of nebulae were literally "in Technocolor". But nobody there was an experienced visual observer (it is safe to assume) and no detailed description of the views could be found in that popular astronomy article. In one way or another, the larger the aperture, the less reliable information we may have about what was actually seen.

Theoretically in presence of color contrast, color perception benefits from the angular size of the differently colored features. So the surface brightness and exit pupil considerations may not always be limiting. How this translates to practice - what objects, apertures, and magnifications - I have no idea.


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jgraham
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Re: How much aperture for technicolor? new [Re: IVM]
      #5698118 - 02/24/13 11:32 AM

Many years ago a good friend of mine who was a very experienced deepsky observer had a chance to look through the 60" on Mount Wilson. He remarked how absolutely wonderful the colors were, something that images have never been able to capture faithfully. Unfortunately, he passed away a few years ago and he is the only person that I know who has looked through a telescope of that size. It would be interesting to hear from others that have. I also saw that they are working to modify the 100" Hooker reflector with an accessible eyepiece through a set of relay optics. Now THAT would be neat.

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joelimite
Carpal Tunnel
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Reged: 09/01/08

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Re: How much aperture for technicolor? new [Re: jgraham]
      #5698178 - 02/24/13 12:21 PM

We'll have to ask Mike when he's done building his 70-inch reflector:
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5697218/page...



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Astrojensen
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Re: How much aperture for technicolor? new [Re: joelimite]
      #5698242 - 02/24/13 01:11 PM

I have seen M42 in a 30" and there was a lot of colors. Red and blue was quite obvious, along with subtle purple. Most of the nebula was greenish-white, with red and blue seen in streaks here and there, as if applied with a coarse brush, with almost no paint on it.

If I recall correctly, Steve Aggas reported here a while ago, that the core of some bright galaxies were a wonderfully golden hue. I can't remember, if it was M31 or M51, but I think it was one of them.


Clear skies!
Thomas, Denmark


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Sasa
professor emeritus


Reged: 11/03/10

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Re: How much aperture for technicolor? new [Re: Astrojensen]
      #5698271 - 02/24/13 01:27 PM

My former 250mm Newton showed some colors on M42 (and not only to my eyes). There was a red-orange-yellow line.Almost exactly like on this picture

http://astrofotky.cz/~rick/1295969141.jpg

Edited by Sasa (02/24/13 01:43 PM)


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Astrojensen
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Re: How much aperture for technicolor? new [Re: Sasa]
      #5698283 - 02/24/13 01:38 PM

Interesting! I'll look after it with my 12".


Clear skies!
Thomas, Denmark


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Madratter
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Re: How much aperture for technicolor? new [Re: Astrojensen]
      #5698402 - 02/24/13 02:44 PM

I have seen green and pink in M42 (which is probably a best case object). Both are muted in a 20". Technicolor it isn't. But it isn't black and white either. I have a 40mm eyepiece and it is an f/5 telescope. So focal length is 2540 / 40mm = 63.5x. The objective size 508 / 63.5 is an exit pupil of 8mm. In otherwords, even when total dark adapted I'm throwing away some light with that eyepiece.

The point is that is as bright an image of the object as can be obtained with the eye, at a scale large enough that color should be visible if it is going to be visible. The color is still muted.

I'm with Tony on this one. I think the surface brightness of most of M42 (let alone other objects) is just too low for technicolor to result. Muted color in some parts yes.

Besides stars, the most brilliant colors I see from objects in my scope are in planetary nebula. Some of them have very high surface brightness, and the blueish green color in them can be quite vivid.


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mikewirths
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Re: How much aperture for technicolor? new [Re: Madratter]
      #5698475 - 02/24/13 03:46 PM

I've seen obvious pink and green in M42 with direct vision with my 30" dob, but only on nights with low water vapour and excellent transparency. I have also seen red with averted vision in IC418 the small bright planetary. Also have seen aquamarine and blue tinges in other bright planetaries such as the ghost of Jupiter, the Eskimo and Saturn nebulae. I think the key is high surface brightness, extended objects with low surface brightness I don't think it would be possible to see colour, maybe with a huge scope on galactic nuclei (seyfert galaxies maybe?)
Back in 2001 or so a bunch of us(during TSP) had the opportunity to observe all night with the McDonald observatories 82" Otto Struve scope. It was a mind blowing peak experience for a lot of us!!! Most striking was the colour ALL of us saw on objects like the Cats eye and Ghost of Jupiter. We saw totally obvious pastel greens and blues!! We had sub arc second seeing that night but I don't recall anyone seeing colour in the core of M64 (although the structure in the dark lanes was amazing!!).

I'm not sure if they still do nights on the 82" but it seems they still have special nights observing:

https://mcdonaldobservatory.org/visitors/programs/dinner-and-viewing

All I can say is that night gave us all an incureable case of aperture fever!!

cheers

Mike


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GlennLeDrew
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Re: How much aperture for technicolor? new [Re: mikewirths]
      #5698743 - 02/24/13 06:19 PM

For color to be seen, the surface brightness must cross the threshold for stimulating the retina's color receptors. The required intensity depends also on the color, as the eye's response across the visual spectrum varies enormously. And the perceived color, as well as the purity, depends on the mix of colors present.

From my own limited experiments, color detection requires a surface brightness of 18-19 magnitudes per square arcsecond. Many planetaries, few diffuse emission nebulae, many galaxy bulges and numerous globular cluster cores qualify. I doubt if any galaxy spiral arms or reflection nebulae are sufficiently bright.

For continuum sources such as galaxy and globular cores, the colors are subtle, being comprised of stars which collectively are yellowish.

For emission sources, bluish-green dominates because of the eye's much higher sensitivity to O-III and H-beta than H-alpha. To appreciate this, consider: Even though the red H-alpha in IC434 (against which the Horsehead is silhouetted) is of considerably higher intensity than the blue-green H-beta--as amply evidenced by any color image ever made--which filter do you bring to bear; H-beta or H-alpha? Even for such a brilliant nebula as M42, through an H-alpha filter the view is but a shadow of that through either the H-beta or O-III, even though in most parts the H-alpha is as as intense or more so.

This vast imbalance in the the eye's sensitivity to the emission components of glowing nebulae must always be borne in mind.

As we all know, aperture by itself does not alter surface brightness nor contrast; it merely changes image scale for given exit pupil. Once an object has been magnified (via sufficient aperture) to the point of revealing color, larger apertures can improve the perceived color intensity by covering more of the retina. But it cannot ever bring into view color which is of insufficient surface brightness to begin with.


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azure1961p
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Re: How much aperture for technicolor? new [Re: GlennLeDrew]
      #5699036 - 02/24/13 10:30 PM

Thanks guys. I read everyone's responses carefully. I get it but for the small hoice in me keeps asking " yeah but-" - I see aperture too much like the cumulative building of an image like photography/CCD. I KNOW its not the same but...

It does make sense too in that a greater telescope visually will never give MORE light than is present. Galaxies particularly in the film days would need a simultaneous population of SN kicking off to light up like that .

Interesting stuff and thanks.

Pete


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Patricko
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Re: How much aperture for technicolor? new [Re: azure1961p]
      #5699107 - 02/24/13 11:21 PM

I have seen color in M42 with apertures as small as 50mm using large exit pupils ~5mm.

The Merope Nebula shows as blue with a 4.5" Newt with a large exit pupil of 5mm+.

And here is another DSO object I saw color in:

"Hi everyone, I managed to get another look at IC 418 tonight around 8:00pm with the C6. A 19mm eyepiece was used for a power of ~87x. At this power IC 418 appeared to be an out of focus star that fluctuates from light purple to orange and then to pink depending on the seeing. Perhaps even more interesting is that tonight at this power the central star was visible. Upping the power to ~425x greatly enlarged the PN but the central star disappeared completely as did the color seen at lower power. This is indeed a very cool PN!"


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Unknownastron
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Re: How much aperture for technicolor? new [Re: Patricko]
      #5699132 - 02/24/13 11:41 PM

I have seen greenish tints in M-42 with aperture as small as 16", but that was years ago when my eyes were younger. I have seen pink and blue tints which were very faint in 30" and larger telescopes. I have never seen any color in any other diffuse nebula. Now, for planetary nebula, as condensed as they are, I have seen blue or green tints in many, and aperture and transparency help. But all of this color I have seen has been very pale, there are no Technicolor views with visual observing. On this experience works against instead of for you; the younger eyes see color better than older.
Clear skies and clean glass,
Mike


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hbanich
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Re: How much aperture for technicolor? new [Re: Unknownastron]
      #5699231 - 02/25/13 01:47 AM

The largest scope I've looked through so far is the 90 inch Bok telescope on Kitt Peak. Although colors were enhanced, sometimes wonderfully so, they were far from technicolor. Perhaps the most wonderful colors I saw that night were the subtle orange, yellow and blue stars in M13 when the seeing settled down. Saturn's globe looked like a Easter egg. But M57 was still grey, the HII regions of M51 were still grey as were all the other galaxies we looked at. M42 around the Trapezium was an electric turquoise though and had a remarkable texture.

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Rich (RLTYS)
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Re: How much aperture for technicolor? new [Re: hbanich]
      #5699341 - 02/25/13 06:43 AM

I remember seeing a greenish hue in M42 with my 8" Cave Refl.

Rich (RLTYS)


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leviathan
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Re: How much aperture for technicolor? new [Re: Rich (RLTYS)]
      #5699357 - 02/25/13 07:07 AM

I've red a lot of comments on "green" M42 starting from 8" aperture, however I couldn't see neither in 8", nor in 24". So far the only deepsky objects that are color for me - are planetary nebulas.

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GlennLeDrew
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Re: How much aperture for technicolor? new [Re: leviathan]
      #5699486 - 02/25/13 09:31 AM

Patrick,
I wonder if the perception of blue in the Merope nebula wasn't influenced by the bluish light of Merope itself. The surface brightness of this nebula probably doesn't top 22 MPSAS, which would be fully 3 magnitudes below the color detection threshold.

In order to see color, the subject must have sufficient surface brightness to *easily* see with direct vision. The Merope nebula always requires averted vision for me. And I've never seen it as anything other than quite colorless.


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stevecoe
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Re: How much aperture for technicolor? new [Re: GlennLeDrew]
      #5700260 - 02/25/13 05:10 PM

Howdy all;

I don't think that any aperture would produce "technicolor". The human eye just does not gather light in that manner.

However, using Tom Clark's 36 inch f/5 Newtonian many years ago we were blessed with a terrific evening. Using a 27mm Panoptic eyepiece, M 33 was amazing. I could see the two populations of stars. By that I mean that the core was sunshine yellow and the arms were a light blue-white with LOTS of mottling. We all climbed up and down the ladder several times to marvel at the detail and color. You know that one reason a big Newt provides better views is that at the eyepiece you are closer to the stars;-)

Clear skies to us all;
Steve Coe


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Patricko
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Re: How much aperture for technicolor? new [Re: GlennLeDrew]
      #5700645 - 02/25/13 09:48 PM

Hi Glenn, under my skies at ~4300 ft above sea level the Merope Nebula and Maia Nebula are both seen with direct vision under good conditions by me with large exit pupils using a 4.5" f/4 reflector. My C6 SCT also shows them well but it is hard to get large exit pupils with my current setup. I have found that large exit pupils, not aperture, really help in this department.

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