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PeterSurma
super member
Reged: 08/24/06
Posts: 122
Loc: Heidelberg, Germany
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At several occasions I've observed the very positive effect of field sweeping (well, i.e. just moving the scope back and forth across th eobject by +-1 EP diameter) in two areas:
1. finding + observing really faint (low surface brightness)stuff, e.g. local group dwarfs or faint dust features (pillars of creation, M31 dust features)
2. seeing sharper detail in objects, especially on planets (jupiter), but also on DS objects
Anyone here with experiences in this topic (especially #2 which puzzles me) ?
Also I ask myself about (scientific, links) explanations on why + how this works in the human eye/brain ? (well yes I know evolution has trained us to see faint moving details in the dark in order to survive, but how does it actually work ?)
Thanks for sharing your experience + insights.
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Peter
Web: http://www.eyes4skies.de/home_EnglishVersion.htm
Scopes: From 3inch photographic APO to 20inch f/4 Dob
Edited by PeterSurma (11/06/09 05:08 PM)
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JayKSC
scholastic sledgehammer
Reged: 01/01/05
Posts: 985
Loc: Florida
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Hi Peter,
I'll try to answer some of this off memory, so don't consider this to be authoritative!
Part of the eye functioning is to filter data such that only pertinent information is attended to. Otherwise, the huge amount of visual stimuli that is absorbed each millisecond of viewing anything would be simply overwhelming. Thus, the eye naturally attends to certain stimuli more readily than others. Moving stimuli elicit a more immediate attentive response than non-moving stimuli.
In operating, the eye has two general movements that are always active (I consider vergence pursuit to be related to smooth pursuit, but that's another story). One is saccads. Saccads are quick sudden movements that jump from one target to another. Saccads can be involuntary. When viewing a deep sky target on the verge of perception, for example, your eye will likely involuntarily shift from your target to some field star - perhaps a faint field star that suddenly flickers into view and attracts attention. In comparison, smooth pursuit is performed when your eye tracks a moving target. Unlike saccads, you cannot actually control smooth pursuit. You can shift your eyes from one target to another at will, but actually making them move smoothly in response to some moving object is involuntarily. Interestingly, this is why police have individuals suspected of DUI track a pen - the smooth pursuit eye movements are involuntary and are inhibited by alcohol.
Back to astronomy... if your target is moving smoothly I'd suspect that you can follow it with smooth pursuit which disrupts involuntary saccads. Therefore, I'd venture to guess that the smooth pursuit actually allows you to contribute greater visual attention to your target than would be allowed with viewing a stationary object. We know this process to work because in laboratory tests, it's easier for people to follow visual targets on the very verge of detection when those targets are moving than when they are stationary. I'm unaware of the precise mechanism involved, but would suspect it's related to the smooth pursuit eye movement.
- Jay
South Florida
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Refractor manic. 
My Sketches
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Jim Curry
sage
Reged: 10/29/07
Posts: 432
Loc: Maine
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Peter:
I'm not going to touch the technical on this subject but yes, I regularly use my hand controller to sweep across a field to pick up threshold objects. Once I detect the object then I settle down to averted viewing.
Jim
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Vixen 140 refractor
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PeterSurma
super member
Reged: 08/24/06
Posts: 122
Loc: Heidelberg, Germany
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Hi Jay + Jim,
thanks for your remarks. Yes, I've also heard colleagues state that the effect has something to do with involuntary eye movements and their interference with the movement.
I've used field sweeping for years to find weak objects like dwarfs and such, and I also have not that much of a problem with this. It seems pretty natural to me. Even sub-sky-brightness dwarfs or dust features with low contrast stick out of the sky with this method. And as you say Jim, as soon as you've seen them moving, you may stop moving and then still see (or remember) more than before.
What really did amaze me was the fact that object features can become drastically sharper by movement. I've noticed this at two very different occasions:
a) Observing Jupiter normally bores me a bit, since I'm more interested in DS stuff, but also: I don't see THAT much of detail in my 20", I must admit. However, I recently tried to sweep the scope across Jupiter, and I had the amazing impression that I could see MUCH MORE detail then. Features in the clouds, etc, simply much more small-scale stuff. It's not easy to consciously track + tell the real details because they move, but my impressiion really is like an unsharp image suddenly jumping into better focus, as soon as I start moving the scope. Really amazing, and I am pretty sure that this observation is real.
b) Observing dust features in M31 recently I had the impression that I can see the two large dust lanes become much sharper and feature-rich in detail as soon as I move the scope across. Again it's hard to exactly tell which details I actually see, but the effect is surely there. Same effect was seen in observing the most south-western pillar of creation (the small sharp-edged one) in IC4703/M16...
It's really amazing ! - so I wonder about the mechanisms involved here and how to possibly exploit the fact for observing tough DS stuff...
--------------------
Peter
Web: http://www.eyes4skies.de/home_EnglishVersion.htm
Scopes: From 3inch photographic APO to 20inch f/4 Dob
Edited by PeterSurma (11/07/09 03:27 PM)
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auriga
scholastic sledgehammer
Reged: 03/02/06
Posts: 795
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Quote:
Hi Peter,
I'll try to answer some of this off memory, so don't consider this to be authoritative!
Part of the eye functioning is to filter data such that only pertinent information is attended to. Otherwise, the huge amount of visual stimuli that is absorbed each millisecond of viewing anything would be simply overwhelming. Thus, the eye naturally attends to certain stimuli more readily than others. Moving stimuli elicit a more immediate attentive response than non-moving stimuli.
In operating, the eye has two general movements that are always active (I consider vergence pursuit to be related to smooth pursuit, but that's another story). One is saccads. Saccads are quick sudden movements that jump from one target to another. Saccads can be involuntary. When viewing a deep sky target on the verge of perception, for example, your eye will likely involuntarily shift from your target to some field star - perhaps a faint field star that suddenly flickers into view and attracts attention. In comparison, smooth pursuit is performed when your eye tracks a moving target. Unlike saccads, you cannot actually control smooth pursuit. You can shift your eyes from one target to another at will, but actually making them move smoothly in response to some moving object is involuntarily. Interestingly, this is why police have individuals suspected of DUI track a pen - the smooth pursuit eye movements are involuntary and are inhibited by alcohol.
Back to astronomy... if your target is moving smoothly I'd suspect that you can follow it with smooth pursuit which disrupts involuntary saccads. Therefore, I'd venture to guess that the smooth pursuit actually allows you to contribute greater visual attention to your target than would be allowed with viewing a stationary object. We know this process to work because in laboratory tests, it's easier for people to follow visual targets on the very verge of detection when those targets are moving than when they are stationary. I'm unaware of the precise mechanism involved, but would suspect it's related to the smooth pursuit eye movement.
- Jay
South Florida
Jay,
Sorry, I don't follow your explanation.
You are saying that saccads are sometimes involuntary and smooth pursuit is sometimes involuntary?
What then is the relevant difference for amateur astronomers? Does it have something to do with something being involuntary?
Bill Meyers
Edited by auriga (11/08/09 12:34 PM)
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Carol L
Reged: 07/05/04
Posts: 6034
Loc: Tomahawk, WI 45N//89W
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Hi Peter, i've found that tapping the OTA produces better results than sweeping the field. Yes, a moving target is definitely easier to see than a stationary one, but a 'dancing' target is even easier. 
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PeterSurma
super member
Reged: 08/24/06
Posts: 122
Loc: Heidelberg, Germany
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Hi Carol,
OK, I'll try to check this next time. However, our european wheather currently seems really bad bad bad... 
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Peter
Web: http://www.eyes4skies.de/home_EnglishVersion.htm
Scopes: From 3inch photographic APO to 20inch f/4 Dob
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