Field sweeping - experiences & mechanisms ?

[petersurma]

I guess, we all use averted vison AV, where required. Of course, it's a very helpful technique.
It needs a bit of getting used to. You have to step back from the normal bright light perception mode: you try to perceive sth, but still you look aside. Then by focusing your mental attention to the 'side image' you get a deeper detection level. Simply because the retina is more sensitive to low light outside the fovea centralis (aka optical axis receptors). That's pretty easy so far, also pretty straightforward to understand/explain (except maybe the mental attention thing).

Now field sweeping is similar, in as far as it requires some special 'attention mode', too.
Is it also so straightforward to explain - in terms of mechanisms ? I'm not sure.

Most of us might have employed the technique of field sweeping FS as well. I.e. moving the telescope over some faint fuzzy in order to increase the level of perception somehow. This seems to work because evolution has trained our eye/brain system to recognize moving things very easy, because of suspected urgency. The leopard is after you, you better have a special operation mode for that... There is no doubt an evolutionary benefit from having such a mechanism built in.

Some observational examples:

I've used FS many times at faint stuff and low contrast situations. Hunting the horsehead B33 in a smaller telescope you better first find the edge of IC434 running N-S. Moving the scope perpendicular to it (E-W) will help a lot detecting the edge. Then you go for B33 and try the same maybe... The visual system VS (eye + brain) performs something like an edge detection. In image processing there are specific filters for such tasks. In some way or the other the VS achieves the same with similar methods, I guess.

Same for e.g. the pillars of creation in Eagle Nebula IC4703/M16. The smallest pillar is a bit of a stretch. Try to use field sweeping and hey it pops up (well hopefully).

There are more examples, also some interesting ones (I might add some below lateron :-).

FINALLY a somewhat more complex finding:

I noticed that - when moving - the resolution of the image (as) I perceive (it) suddenly jumps up. At rest, with low contrast, I first see some foggy smeared out image, say resolution seems like 10arcsec (because of the low light level). I know that at low light levels the retina cells are coupled by the VS to increase the S/N ratio (I guess pretty much like a CCD would be binned to reduce the read noise, if not sky-limited). Now, when I move the image resolution suddenly seems to jump to say 3 or 1 arcsec (i.e. by a pretty large margin). At least - to my brain - this seems the subjective impression I have. Of course, I have a hard time then CONSCIOUSLY recognizing things while they move - so fast, and so many details simultaneously ! But still it looks/feels like increased resolution.

I really also notice this sometimes when I look e.g. at Jupiter with good seeing (I hardly do, it spoils my darkness adaptation, of course). As soon as I move my scope the image looks much sharper, all of a sudden. I see cloud details that were hidden when at rest.

I would really be curious if you could comment (especially) on this latter finding / impression / subjective observation.
Any scientific facts on this (from VS physiology etc) ?
Is your experience/feeling about FS similar or totally different ?
Any situations where it seemed especially evident / useful ?
For those in the sketching business: what about the importance of panning to you while you observe + sketch ?


Thx for comments.