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question for the seasoned visual observers....

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#1 dkbender

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Posted 28 October 2013 - 07:31 PM

I just got my ES ED152CF up and running this past weekend and enjoyed Hercules Cluster, M92, M57, M31 and so forth... The technique I was using was to hood my head and eyes for complete darkness and with the TV 6mm Delos EP, I was getting really good contrast with really black background and after looking with averted vision, I could finally see one dust lane in M31.... but what really got my attention, was when I was looking at M92 for example, there is this background fabric in the black that seems to have a pattern. What is that? Is that billions of really low magnitude stars that my eye and brain are assimilating into patterns in the background??

#2 kfiscus

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Posted 28 October 2013 - 08:29 PM

Billions is overstating it, but it's a least a few hundred thousand. Congrats on the new rig.

#3 dkbender

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Posted 28 October 2013 - 08:35 PM

Thanks Ken,

So that patterned "fabric" on the black I'm seeing is 100's of thousands of stars, that I can't individually resolve but they form an overlay on the black and my brain is forming visual patterns.

Just wanted to know for sure what I'm looking at.

#4 stevecoe

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Posted 28 October 2013 - 09:36 PM

Dave;

My observing buddy and I have been using the "monk's hood" for decades and have found it really helps the contrast. I use a piece of black cloth and A.J. uses a Navy Blue towel.

When I had a TV 102 it really helps with many open clusters. Lots of faint stars resolve in that fuzzy background. Get good with averted vision as well.

There are many articles about a variety of deep sky objects in the CN archives. Go to "articles" at the top of the page and then to "monthly" and "What's Up". They contain a variety of objects to enjoy.

Clear skies;
Steve Coe

#5 GlennLeDrew

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Posted 28 October 2013 - 10:01 PM

This 'background fabric' could simply be your visual system 'noise' manifesting itself in the darkened sky resulting from the small exit pupil.

#6 kfiscus

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Posted 28 October 2013 - 10:14 PM

The noise idea is intriguing. It would be interesting to know if you could see the same 'fabric' effect away from M-92 or anything else. If it's stars on the edge of resolution, you should see more as you approach the glob and fewer as you move away.

#7 george golitzin

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Posted 28 October 2013 - 10:46 PM

I'm with Glenn on this one. When you're well adapted and all extraneous light is excluded, you come up against your own visual noise, particularly if you're at high power trying to nail down some faint object in a quiet field. This experience is to visual detection what seeing the Airy disk is to resolution. That is, when you see the Airy disk, you're up near the resolution limits of your scope; likewise, when you see that background noise, you're near the limits of visual detection for your scope on that night.

However, if you're in the middle of the milky way, it's a different situation--E.E. Barnard talked about seeing "strata" in milky way fields, and it does seem like that some times. Here I think the variations or patterns in contrast have more to do with attenuation by dust, but I could be wrong.

-george

#8 galaxyman

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Posted 28 October 2013 - 11:16 PM

I also agreed with Glenn.

Anyway, it's good to read some DSO observing using a quality large refractor :waytogo:

Karl
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#9 dkbender

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Posted 29 October 2013 - 07:40 AM

wow! so it's possibly an artifact of my eye/brain visual system. But we are not sure.

I just got back into astronomy after a 43 year hibernation period. I don't remember seeing this with my 6" Newt when I was a teenager. I do not see it currently with my 12" Dob but I have seen it with my 4" apo and now with the 6" apo. I figured it had to do with the better contrast but I also figured it was a universe "clouds" of untold numbers of unresolvable starlight in the background. If my head and eyes are un-hooded, I don't see it. The instant I hood my head, I see it.

So, is this another one of those things, that makes you go... Hmmmmmmmmmmmmmmmmm........????

Oh Karl, I'm loving apo's right now because of the image fidelity, even though the aperture isn't very large, I love the quality.

#10 aatt

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Posted 29 October 2013 - 10:56 AM

I have visual "noise" a lot. It makes for some dicey views on low contrast objects. This did not used to happen back in the day, but I am pushing 50 now and need glasses....

#11 dkbender

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Posted 29 October 2013 - 11:30 AM

I just read the description of broadband visual snow and that does not seem to fit what I am perceiving visually.

It's interesting because when I look at the Double Cluster, I don't notice it in the black background. When I switch to the Hercules Cluster or M92, it appears in the black around the cluster but does not interfere with my ability to use my averted vision and see minute details in the clusters.

#12 WeltevredenKaroo

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Posted 29 October 2013 - 02:57 PM

Is your body leaning forward into a somewhat cramped curl as you observe objects higher than ~45°? I notice the effects you describe while leaning forward while bending my neck backwards during high-azimuth observing. Body builders train themselves to be aware of under ventilation while doing ab curls. The diaphragm becomes overcompressed without our being aware of it because we're concentrating on doing or seeing something else. Ophthalmologists describe the flickering shimmer you describe as retinal noise from oxygen-deprived synapses. Shallow breaths or unintentionally holding the breath while teasing out that elusive faint fuzzy underoxygenates the blood. The quick fix is hyperventilating the way sharpshooters and archers do—three fairly slow, deep breaths followed by a half-exhale and then pulling in the upper ab muscles and holding the breath. This both supplies and squeezes oxygen flow into the blood. It takes a bit of practice to avoid over oxygenating and its dizziness. When I do this, the false shimmer disappears within seconds and I can see a full magnitude deeper in fully black fields for about 15 seconds. While observing with others, I frequently see objects a magnitude or more fainter than my friends. When I described the hyperventilation technique, they see what I do.

#13 dkbender

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Posted 29 October 2013 - 06:38 PM

Is your body leaning forward into a somewhat cramped curl as you observe objects higher than ~45°? I notice the effects you describe while leaning forward while bending my neck backwards during high-azimuth observing. Body builders train themselves to be aware of under ventilation while doing ab curls. The diaphragm becomes overcompressed without our being aware of it because we're concentrating on doing or seeing something else. Ophthalmologists describe the flickering shimmer you describe as retinal noise from oxygen-deprived synapses. Shallow breaths or unintentionally holding the breath while teasing out that elusive faint fuzzy underoxygenates the blood. The quick fix is hyperventilating the way sharpshooters and archers do—three fairly slow, deep breaths followed by a half-exhale and then pulling in the upper ab muscles and holding the breath. This both supplies and squeezes oxygen flow into the blood. It takes a bit of practice to avoid over oxygenating and its dizziness. When I do this, the false shimmer disappears within seconds and I can see a full magnitude deeper in fully black fields for about 15 seconds. While observing with others, I frequently see objects a magnitude or more fainter than my friends. When I described the hyperventilation technique, they see what I do.


Hi!

I've been to RSA twice. Once in 2002 and again in 2004... loved it there! I was on safari both times. Koffiefontein area the first time and Blomefontein area the 2nd time. Sat out many nights, after the campfire went out, looking at the lovely southern hemisphere sky and marveled at the Southern Cross.

To your post, head/neck position and breathing have nothing to do with it.... but thanks!

#14 Kraus

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Posted 30 October 2013 - 08:30 AM


I too use a black shroud to block stray light. And depending upon how dark adapted my eyes get underneath, I see some other things as well. I just write it off as my eye's pupil is so wide, anything is visible.

Visual system 'noise'!!! Har-dee-har!!!

#15 george golitzin

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Posted 30 October 2013 - 12:37 PM

I too use a black shroud to block stray light. And depending upon how dark adapted my eyes get underneath, I see some other things as well. I just write it off as my eye's pupil is so wide, anything is visible.

Visual system 'noise'!!! Har-dee-har!!!


Har-dee-har?

The study of visual systems is a huge area, and noise is certainly an important topic. In one study of the minimum visual stimulus necessary to evoke a human response, the authors found that while the detection of a pulse of 147 photons (a statistical average, obviously) with 60% frequency of seeing resulted in only a 1% false-positive rate (FPR), the detection of a 34-photon pulse with 60% frequency of seeing raised the FPR to 33%. They deduced that the detection of a single photon with 60% frequency of seeing would entail an FPR of 55%.

So when it's really dark under that hood, you're seeing a number of bogus photons.

http://www.opticsinf...ct.cfm?id=58340
http://sws1.bu.edu/t...72-419-1982.pdf

-geo

#16 WeltevredenKaroo

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Posted 30 October 2013 - 03:27 PM

It helps to do the homework before the har-dee-har. Google 'visual stimulus at low light levels'.

#17 george golitzin

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Posted 31 October 2013 - 12:13 AM

I'm going to try the hyperventilating technique, Dana, thanks for the tip.

-geo

#18 RussL

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Posted 31 October 2013 - 11:39 AM

I have heard what you're seeing being called "the lumpy darkness" (someone on here said it a few years ago, I think it was). I see it often when out at night. I didn't notice it until my latter years (I'm 63 right now). Maybe it was there all along to some degree, I dunno. It does indeed make me think maybe I'm seeing something else that isn't ther, possibly. I used to think maybe it was the "fabric" of space, for lack of a better term, although I have no idea if there's anything like that to be detected. The talk of visual noise makes sense. I would assume that each of us varies to some degree in how we see it, or even how much we see it.

#19 george golitzin

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Posted 31 October 2013 - 07:11 PM

I have heard what you're seeing being called "the lumpy darkness" (someone on here said it a few years ago, I think it was). I see it often when out at night. I didn't notice it until my latter years (I'm 63 right now). Maybe it was there all along to some degree, I dunno. It does indeed make me think maybe I'm seeing something else that isn't ther, possibly. I used to think maybe it was the "fabric" of space, for lack of a better term, although I have no idea if there's anything like that to be detected. The talk of visual noise makes sense. I would assume that each of us varies to some degree in how we see it, or even how much we see it.


I think it's reasonable to use the term "lumpy darkness" for this phenomenon, but the term is also used in connection with galaxy clusters, such as the Corona Cluster, where the lighter lumps are real objects--the (small, high-mag) field of view appears mottled because it is so full of unresolved galaxies, some of which occasionally coalesce into view under prolonged concentration and changing seeing conditions. That's an eerie experience.

-geo

#20 dkbender

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Posted 31 October 2013 - 10:01 PM

So, riddle me this....

If I close myself in a completely dark closet and stay in there to dark adapt my eyes, it's now pitch black, as dark or darker than looking in the eyepiece with my head hooded and I don't see the same phenomenon. Why is that? If it's visual noise, I should see the same lumpy darkness in the closet, right?

#21 george golitzin

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Posted 31 October 2013 - 11:47 PM

Well, have you actually performed that experiment? And if so, are you staring hard at the darkness for a prolonged period trying to see something, as at an eyepiece, or are you letting your eyes wander all over? In experiments trying to determine the minimal stimulus to trigger a visual response, the participants are expecting to see something, and are trying to see something, much as you are at the eyepiece. This leads to false positives. That's not the case in a darkened closet. Other weird stuff happens in a darkened closet, if you stay there long enough :)...in cases of prolonged sensory deprivation, do not people begin seeing all sorts of stuff that isn't there, the brain trying to fill in for what is missing?

Bottom line, I'm no expert on this subject, but I'm pretty convinced I'm dealing with visual noise a lot when I'm out there trying to pull in threshold objects. And I don't know if we're seeing the same thing or not, but I think visual noise, or else the brain's tendency to fill in patterns that aren't there (like Lowell's canals on Mars) is a likely candidate for what you (and I) are seeing.

-geo

#22 GlennLeDrew

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Posted 01 November 2013 - 04:57 AM

Whether in complete darkness or with eyes closed in a well darkened room, I always see a kind of scintillating pattern in the blackness if I look for it. When not thinking about it at all, I notice nothing but the darkness. (If this 'noise' were not so easily ignored--it is suitably subtle, thank goodness--I almost wonder if it sometimes wouldn't interfere with sleep.)

#23 dkbender

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Posted 01 November 2013 - 09:58 AM

Hi George,

Yes actually, I have. I get a subtle pointillism effect but it looks and reacts completely differently from what I am seeing in the 2 apo's. Which is why I originally asked the question. The effect at the EP with the 2 apo's is like turning a switch on, when I hood my head & eyes and immediately there is this "texture" in the black. I don't have to stare hard at it, I don't have to coax it out.... it's just right there, instantly. I'm in a comfortable position, I have varied my breathing... it doesn't make any difference. It's so repeatable, I just came to the conclusion that it must be subtle, distant below resolution, background light out there but I wasn't 100% sure, which is why I asked the original question.




Hi Glenn,

I do get the very subtle pointillism effect in the dark but it is easy to distinguish.

#24 george golitzin

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Posted 01 November 2013 - 03:13 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

#25 DavidNealMinnick

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Posted 01 November 2013 - 03:48 PM

are you staring hard at the darkness for a prolonged period trying to see something, as at an eyepiece, or are you letting your eyes wander all over? In experiments trying to determine the minimal stimulus to trigger a visual response, the participants are expecting to see something, and are trying to see something, much as you are at the eyepiece. This leads to false positives. ...in cases of prolonged sensory deprivation, do not people begin seeing all sorts of stuff that isn't there, the brain trying to fill in for what is missing?

-geo


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.






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