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question for the seasoned visual observers....

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#26 dkbender

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Posted 02 November 2013 - 10:16 PM

Hi Dave-

Okay, that's interesting. For my part, I notice something like Glenn's scintillating pattern, or perhaps your pointillism--to me, a kind of mottling in the background that is in flux. (With occasional bogus point sources, unfortunately!) Do you recall the nature of the pattern you see? Is it mottled, or striped, or tendril-like, etc?

Again, when looking within the band of the Milky Way, who knows what is creating the patterns. There is a general wash of light from thousands of unresolved stars, there is lots of intervening dust, etc., and all this creates subtle patterns, to me often striped--Barnard's "strata." But I don't see this when looking out of the Milky Way. Outside the Galactic plane, I tend to see that eye-brain mottling I mentioned. But I need to pay closer attention, perhaps.

Now, Hercules is not far out of the galactic plane, so maybe you were seeing something real. Do you get the same effect in Coma Ber. or Sculptor, for example? And how about within the Milky Way itself? If there is a uniformity to the experience across the sky, I think that is an argument for an eye-brain phenomenon.

-george


Hi George,

I would say the appearance of what I'm seeing is what I would call mottled.... and it is subtle.

I'll keep looking at it and report back when I can add to the description and further the discussion.

Thanks for the replies!

#27 dkbender

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Posted 03 November 2013 - 09:07 AM

So, I was perusing the previous owner's AP catalog using the ED152CF that I own now and found a photo of M13 that he had taken in June of this year. I looked at it and saw the mottled texture in the black background that I have been trying to figure out what it is.... take a look and you'll see what I've been asking about... What I notice is, that during visual observation at the EP, using the hooded technique, it is even more obvious than what is in the photo below.

http://www.astronomyphotos.com/M13.htm

#28 Anthony236J

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Posted 03 November 2013 - 05:05 PM

Hi Dave,

Congrats on the new scope!

It looks like that photo is displaying some noise. If what you see in the eyepiece is of a similar pattern and uniformity, I would guess that it is also some type of noise. It seems that if you see this kind of pattern at the threshold of detection in a 4" telescope, then its structure should be even more evident in a 12" telescope under the same conditions.

That would be my guess without knowing exactly what you are seeing.

#29 Asbytec

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Posted 03 November 2013 - 08:34 PM

I wasn't wearing my hood at the monitor, so took the liberty to enhance the noise and see what you're talking about. There is a molted background. Is this what you're seeing? That molted pattern?

I think Ken's question above is pertinent, does it appear near brighter sources or in the darkness of space (like being in a closet?) If the camera picks it up (after applying a flat frame?), and if this is the same source of the molted pattern, then it's likely not entirely in the eye brain system. It seems very dim and that you pick it up at all is testament to your dark adaption.

But, like others, with eyes closed I get some light and dark interplay, but if memory serves...been so long since I even paid attention, the patterns are in motion. Sometimes while observing I get a speck that appears, but as we all know those are meteors coming directly as us or a UFO sneaking into the upper atmosphere. :)

In the end, I can't say I remember seeing such a molted pattern against the black of space. Not to the extent it became bothersome, or at least never gave it (visual noise) a second thought while focusing on the object at hand.

#30 azure1961p

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Posted 03 November 2013 - 09:52 PM

With out reading the whole thread it sounds like its your eye-brain trying to make sense of the myriad stars just beyond your visual threshold or teetering on it. Singly for example these stars would probably not be seen at all but as a cumulative glow its probably being sensed on some level by you and patterns and such are the brains way of bringing understanding to it.

Just a thought.

Pete

#31 dkbender

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Posted 04 November 2013 - 02:00 PM

Anthony, Norme & Pete,

At this point, I've only noticed it around M13 & M92. I had a real good view of M57 but was so captivated by seeing the shades of nebulosity in the ring, that I didn't notice the background texture on that particular view. As previously noted, I had a real good view of the Double Cluster and did not notice it there either.

I'll keep looking and report back any further clarification or new findings.

#32 Sarkikos

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Posted 08 November 2013 - 02:25 PM

During my term in the Army I can remember vividly nights while out on a Field Training Exercise(FTX), staring out of a foxhole at the forest during the wee hours trying to detect Rangers tasked with infiltrating our lines, and seeing things "move" when nothing was moving at all.


IME at night, if I'm looking at a row of trees at the edge of a woods in the distance it's easy to mistake the dark gaps between the trees for people standing together and milling about. Sometimes it even seems that the people are moving around. It can be a little unnerving until you realize that they're only trees.

I've read that sometimes soldiers have fired at trees - especially during low light conditions - mistaking them for the enemy. This happened often during the Civil War.

Mike

#33 choran

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Posted 12 November 2013 - 04:26 PM

"Lumpy darkness" is exactly it! Great description. I see what looks like a black quilt, mainly black, but with a seeming pattern of light areas. I have assumed, with no real evidence, that it is a background of very distant/faint stars, but I'm not at all sure. I see it through all of my scopes, and even with binoculars occasionally. Is it possibly just an artifact of magnifying a couple of hundred miles of atmosphere, with its dust, smog, etc? Doesn't seem likely, but I just don't know. I am more conscious of it at higher powers, but as I say, I can even see it in binoculars at times. Wish I knew for sure.

#34 Starman1

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Posted 12 November 2013 - 06:55 PM

A few comments:
1) Look at the background in Sagittarius in the Milky Way. The sky appears 'grainy', which is incipient resolution of extremely faint multitudes of stars. You might also see this in Cygnus with the naked eye.
2) Look at the ground or surroundings (but not the sky) once you have dark adapted. You may see, as I do, your visual reality break up into a series of dots--the 'pointillism' of visual reality when insufficient light is entering the eye. Is it noise in the retina? Perhaps.
3) Look at a star cluster of moderately bright stars (say, NGC7789 in Cassiopeia). Do you see the stars all surrounded by very slight fuzziness that makes the stars look as if they all sit on stalks pointing at you? If so, this can be evidence of dew beginning to form on the optics (eyepiece, or lens or mirrors). In fact, this can cause the 'mottled sky' effect you mention.
4) Visual noise appears in differing ways. When I look at a galaxy cluster I can 'see' galaxies where there are none, and sometimes not see ones where they really are. When you observe at the limit, visual noise often appears 'real'.
5) Have you sought stars at the very limit of your scope by using some magnitude charts for specific areas? Stars at the very limit are only visible to averted vision a small percentage of the time. If a star winks in, it appears as a very small pinpoint.
If a galaxy or nebula fragment just winks in, it appears as a slightly brighter portion of the background sky. This makes identification difficult. I usually have a chart of the area of the faintest targets so I can look exactly where it is. This increases the odds that something that winks in and out of visibility is real and not just noise in the eye+brain combination.
6) Stars "move" when you stare at them if the patterns are arranged to fool the eyes. A recent thread here on CN had a chart with a series of ovals on it, arranged in vertical and angled rows. The ovals crawled back and forth and seemed to undulate. When you stood back several feet from the monitor, they stopped moving. I often see objects at the limit, especially stars, crawling in position. This is an example of where the eye and brain are being fooled.

if you study many of the references on the web concerning vision, you will see how easily fooled the eye is. Stare some time at a uniformly black piece of construction paper in a poorly-lit (or very dimly-lit) room. The black paper appears mottled and sometimes shows gray patterns on it. This is the poor visual system nature gave us to deal with really low light conditions.
Despite that, we do have better night vision than you might expect for a daytime animal. It probably had significant survival value in the youth of our species.

But it obviously isn't perfect. :grin:

#35 MrJones

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Posted 12 November 2013 - 10:13 PM

When I first learned about visual noise it was called hallucinations. As per above there's been a lot of research in the area. Also look up Eigengrau.

CEV wiki

Eigengrau wiki

#36 dkbender

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Posted 13 November 2013 - 08:52 AM

"Lumpy darkness" is exactly it! Great description. I see what looks like a black quilt, mainly black, but with a seeming pattern of light areas. I have assumed, with no real evidence, that it is a background of very distant/faint stars, but I'm not at all sure. I see it through all of my scopes, and even with binoculars occasionally. Is it possibly just an artifact of magnifying a couple of hundred miles of atmosphere, with its dust, smog, etc? Doesn't seem likely, but I just don't know. I am more conscious of it at higher powers, but as I say, I can even see it in binoculars at times. Wish I knew for sure.


This is exactly what caused me to post the original question. Black quilt with texture is another good description.

Don, thanks for your thoughts! I'll continue to pay attention and see if I can determine more clues. What is interesting is how when I hood my head and eyes, the quilt, fabric texture literally snaps into place and it is stable... which makes me believe it is real and not an artifact of my visual system.

#37 ronald doane jr

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Posted 15 November 2013 - 03:26 PM

The term for this condition is called visual snow. You can google it for more info.






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