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This is a repeat of my last post in the "Observation Reports" forum, which had to be put there because it follows on from mental4astro's post regarding Observing techniques. However, it now belongs to this forum on how best to observe faint deep sky objects.
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In visually observing a faint galaxy or faint HII region, or observing a faint feature within a galaxy or HII region, I would probably do a combination of the following things:
- looking fixedly, just to one side of the target object, while concentrating on the object itself, for 5-10 seconds, thereby allowing the exposure time of the rods to be used, and thereby allowing an image to build up.
- moving my eyes randomly and rapidly around the field, in order to relax or reset them
- looking fixedly just to one side of the target object again (but looking at the opposite side of the object to the side I looked at first), while still concentrating on the object itself. (again, for 5-10 seconds)
- looking straight at the object, for comparison with the views that I get using averted vision
- moving the telescope, just a very little, from time to time (as mentioned in mental4astro's post), which can make the object more obvious.
I repeat all of these steps when I observe a vanishingly faint Diffuse object, often repeating them many times, and I find that I do gradually build up a better idea about the morphology of the "very very faint object" in the eyepiece. This seems to be an additive process, and the various glimpses that I get of the object (or of features within the object) can be used to build up a better picture of it.
I have been known to persist for up to one hour on a single object, at which point my eyes are thoroughly fatigued.
If I am not sure whether or not I have seen something, I resort to some of the stratagems in my previous post within this thread ("When the eye+brain sees an intermittent feature - is it real?).
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There have been some studies done of how far away from the object, in degrees, your gaze should be centred, in order to put the light from the object onto the most sensitive part of the retina. But there is some individual variation, and this is something that is worth studying!
An important point, as per my above description of observing technique, is that both staring fixedly and (at other times) moving the telescope a tiny bit, are probably necessary to see all that we can see in a very faint object.
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