Averted vision is when you look slightly to the side of something as opposed to looking directly at it. Eg the moon (not that this is a good example but its a easy one) if you look directly at the moon it is in the center of your field of view. However if you look to the left (or any other direction of it) it still in your field of view but your vision is averted from it. This is a good skill to master when looking for dso's and once u know what ur looking for its handy for finding random objects.
Some of the best unplanned observing I have done is locating something by averting my vision and then pointing the scope in that direction to see whats there the fun part is usually trying to work out what the hell I was looking at!
It when you look at the corner of your eyes. Your eyes have more receptors in the sides then they do in the middle. It why you can see more detail when you are looking at something out of the corner of your eyes. So to do it just look to the right or left of the object and you will pick up more detail. I find it not as easy to do and does take a little bit of practice to pick up the detail.
And it's not just a thing for binocular or telescope viewing. When I described it to my sister, before she viewed for the first time, she said that's just what I do when I'm out walking my dog after dark. If I want to see what the dog is doing, I've learnt to look away slightly from the dog and I can more clearly see what is happening from the "corner of my eye".
Also look at 47 Tuc, naked eye, then glance a little away from it. It really jumps out at you then!
As I recall, there are certain directions to glance and they can differ between monocular (telescope eyepiece) and binocular (binoviewer or binoculars). You can also move the image onto your blind spot, if you look the wrong way. You need to experiment. Telescope (monocular) I usually glance towards 2 o'clock.
Remember, also, a moving object can be more readily picked up by the eye. Hence try tapping the scope to make it vibrate. With a dob, it's easy to gently move the OTA a little bit back and forward, up and down - I often do that to confirm I have located the faint fuzzy!
As I understand it, our eyes are evolved for looking directly at brightly objects during daytime and seeing them in colour.
About 10 years ago I was hunting the galaxy Centaurus A from my backyard. I swear I had the 8" pointing right at it, but couldn't see it. I pulled my jacket over my head, had another look around the field of view, and it suddenly jumped out at me when I wasn't looking directly at it. That's averted vision.
Its all in the rods and cones. We have two types of photoreceptive cells in our eyes, rods and cones. The rods are more sensitive but only see in B&W and the cones see in colour but need more light to work properly. Also, they are not distributed evenly in the eye, the cones are more central and the rods further out. If you have plenty of light, like the moon then you can look straight at the object and see detail and colour but if the light levels are marginal the cones are not stimulated and don't work. Then, by looking slightly off centre you focus the light on the more sensitve rods but you only see in monochrome.
This also explains why red light does not effect your night vision. Cones see the red light but the rods only see b&w hence when you see red light you are only using your cones, and it does not desensitise your rods.
Don't necessarily look out the corner of your eye, but just slightly off the side of the object.
The crosses in these illustrations shows where I mean.
In the 1st image, Top section shows what a DSO looks when looking at the yellow cross.
Bottom section shows the same DSO if you look where the yellow cross is. (it doesn't work on this scale so don't expect to see the galaxy brighter by looking at the cross in this example)
In the 2nd image I give some examples of some places to look in the eyepice. The object in the centre will appear brighter when looking at the white crosses. (again, not in this sample, only in the real eyepice)
My understanding was that averted vision worked because you have a 'blind' spot in the retina where the optic nerve is which doesn't matter in normal circumstances but when looking at a very dim object represents a loss of resolving power due to the reduced active area. Thus by using slightly averted vision you get more of the light that is entering your eye from that object falling onto the rod cells.
Incidentally, if I recall correctly your rod cells are primarily seeing green, but your brain interprets it as monochromatic and bases it's colour perception solely on the the input from the various cone cells. So the red light isn't activating the rod cells unless it is fairly bright.
Apart from Rods and Cones, and blind spots, another factor that also dims direct observation is that a certain percentage of light bounces of the Retina and straight back out of the eye through the centre.
By slightly averting your vision, the light is bounced off at an angle and mainly remains in the eye.
The blind spot is where the optic nerve leaves the eye and there are no receptors, either rod or cone. Its not a problem with binocular vision as each eye compensates for the other, but can be a problem in monocular vision, but only off center as the center of our vision, the fovea (aka the macula), is rich in cone cells. So the blind spot can become a problem when we use averted vision. The reason for using averted vision is that the fovea has no rod cells, only cones and is therefore not useful for low light vision (as described in previous posts). Rod cells are located away from the fovea so averted vision helps when light is low. When I was studying this stuff in physiology some 25 years ago, there was some evidence that a fully dark adapted human rod cell will respond to 1 photon of light in the visual spectrum, provided it isn't red light. If 2 rods within 10' arc go off, it will be perceived. This is equivalent to seeing a candle at 30 km. I don't know if more recent work has confirmed this. Dark adaptation is the replenishing of rhodopsin, the pigment that absorbs light and triggers the electrical activity in the cell. When a bright light is seen, the rhodospin is exhausted and the cells will take up to 40 minutes of darkness to restore it fully.
Averted vision is a term used to describe what happens when a hot member of the desired sex walks down the street and notices you staring at them.
Averted vision is the #9 cause of minor traffic accidents in the United States.
Averted vision is best avoided by wearing sunglasses so one can gaze with impunity.
SJS
BTW, the Blinking Planetary in Cygnus (ngc6826) was, in fact, named for its blatant change in appearance while alternating direct and averted vision.
It lies 5.4 deg due north of 3rd mag deltaCyg.
So, as we can tell by the many explanations, averted vision works!
And no matter which explanation is most dominant, or be it an equal mixture of all . . . just look slightly off-centre, in any direction.
Except that, for the record, from the above post it appears I was wrong , it's nothing to do with the blind spot caused by the optic nerve, but is due to the higher proportion of rods relative to cones away from the focus of the eye (fovea)...
Just one more suggestion, if viewing monocular. Keep your other eye open to fully relax the muscles. Get yourself an eyepatch for that eye so you are not distracted with the view of the edge of the focusser and the scope!
Just one more suggestion, if viewing monocular. Keep your other eye open to fully relax the muscles. Get yourself an eyepatch for that eye so you are not distracted with the view of the edge of the focusser and the scope!
Averted vision?
the fun part is usually trying to work out what the hell I was looking at!
, it's nothing to do with the blind spot caused by the optic nerve, but is due to the higher proportion of rods relative to cones away from the focus of the eye (fovea)...
