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One thing I've read so far that is being hinted at is what I call "light saturation" of our eyes. We typically sit on an object, and as the observation time elapses we begin to actually see less in the object than we noticed at the start of the observation. We are not imagining this. What is needed here is to restimulate our eyes. This is somewhat akin to how our nose looses its sensitivity to a particular odor when exposed to an odor for an extended period of time.
Another part to this is how our eyes are made to detect motion. Here's an example: You're looking across a peaceful valley. We see nothing moving, other than a few leaves on the trees (due to the breeze). Unconsciously our eyes begin to dart around, looking for movement (from a possible threat). We spot something out of the corner of our eye, a rabbit shooting off from a stand-still - we didn't see it at first even though it was in plain sight, as it wasn't moving, and the sudden change in light conditions, small as they were, was instantly picked up by our eyes when the bunny moved.
Where I'm heading to here is that a still, unmoving telescope is our biggest impediment. Our eye (or eyes if you're using a bino viewer), darts over the image the eyepiece presents. Low light quickly saturates the rods in our eyes, and we no longer see as much detail.
Solution: give the scope a little tap to set off a vibration, and all of a sudden our eyes begin to see detail! The induced movement restimulates the natural reactivation mechanism in our eyes.
This is something that I had noticed for many years, but wasn't aware that it was of the physiological reason behind it until it was explained to me. I had struggled on occasions to spot very faint objects at times, even though the charts said the object SHOULD be there. Yet, I only noticed it when there was a brisk movement or vibration induced in the scope, otherwise the object seemed to be totally invisible.
This is one reason why I've decided not to motorise my dobs. The constant shifting of the scope I actually now find is most benificial to my productivity.
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