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Primer: Understanding night vision, averted gaze and telescope tapping


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As a relative newbie to astronomy I can't really contribute any tutorials on nebulae and planets, but in the spirit of giving back to this forum, from where I've learnt so much, here is a short primer

I've been reading stuff on this site for a while now but I finally decided to register after reading this just to say thanks.  I learned a LOT from this article and it really helped me understand why

Hi well I have just signed up to this forum with all intentions to ask about equipment and the like. I didn't think that my first post on the forum would be this but after reading this post (one

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Superb post, thanks.

The bit about the pencils reminds me of an experiment I have tried...

Pick a playing card at random and hold it at arms length to one side and gradually move it into your field of (again, the pencils)

On the periphery, you can see something but not really make out its shape. It is surprising how close to the centre of your field of view you have to get in order to make out its colour, suit and value.

The difficult bit is keeping your gaze straight ahead while studying something off to the side. Maybe this is something that gets easier with practice.

It does bring it home how illusory is our view of the everyday world!

--- Penguin.

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Sorry IAN not Colin LOL

1 Question then,

Why doesnt my coffee fall out of its cup? :):icon_scratch::p:D:confused:;)

ROFLMAO

If you read the top sticky about star births and deaths then I believe it has something to do with ice cream :D.

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I love this place! What a great article, Ian, Thank you

It's interesting what you say about the brain adapting to what information it receives, my son apparently has no 3d vision (he was the only person I know who chose to go to see Avatar in 2d!), but he can catch a ball, drive a car etc as his brain compensates for the lack of depth of vision.

Thanks once again

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my son apparently has no 3d vision

Well, clearly he does if he can catch a ball! The thing is, there's much more to 3D vision than the information we get from having two eyes. In fact, the depth cues you get from having two eyes only work over a fairly small range of distances - when something is at any sort of distance (over, say, 50m) the information in each eye is basically the same. And when you're doing something really close up that requires depth perception, like threading a needle, you probably close one eye!

In fact, much of the information we use for judging distance works just fine if you close one eye. I can tell my computer is closer than my desk right now because the computer blocks part of the desk (yes, simple as it sounds, this is actually a major depth cue). We can also tell a lot about depth from parallax effects: move your head and close objects move faster than far objects. There are a load of other, similar cues, which work with one eye. These will be what your son is using.

As my old visual perception lecturer once said: the main reason we have two eyes is most likely so that we have a spare.

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Well, clearly he does if he can catch a ball!

I agree, I don't think it's as plain as described by the Doctors, but it was interesting he was shown an image, and within it you could see the 3D affect of a butterfly - but he just couldn't see it - it was just a jumble of colour to him

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Something to consider is that pictures are very artificial: two-dimensional representations of three-dimensional objects or scenes are effectively a cultural invention and in large part only 'work' because we're taught to interpret them in certain ways - even photographs. For example, if you look at this picture here it probably means almost nothing to you, but to an aboriginal Australian it depicts a meaningful scene because it follows the rules they happen to use to depict images (the semicircles are, I believe, people). We have our own set of rules, which to an outsider are probably just as alien as the set used in that picture are to you. So I wonder if your son just hadn't entirely got on board with the set of rules and principles we use in our culture to depict 3D things in 2D scenes?

To put this in different terms, the rules we in the West use to depict 3D objects in 2D scenes are the rules that M C Escher knew well enough to play with them at will.

Edited by Breakintheclouds
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Interesting - His eyes I'm told work independantly of each other, he's been to see 3D films with his friends but says it's just the same as watching a normal 2D film - surely not a result of cultural intervention? Don't get me wrong, I'm not disagreeing with you - in fact I'm interested what you have to say - even if I'm moving a bit off topic

Edited by MorningMajor
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Great post, thanks.

On the subject of 3D vision, I have a nasty chunck of astigmatism in both eyes (not great for observing - it gets worse the more dialated the pupil!) and even with corrected vision I don't get great 3D images from stereograms or 3D pictures.

Nothing wrong with my 3D vision in the real world though!

...and I suspect this type of test could also be affected by colour blindness so with your son's diagnosis there are at least three possible causes!

Edited by x6gas
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Thank you very much indeed. Your article made fascinating reading and was truly an eye opener (excuse the pun) I have experienced all of the effects you described and over time adopted solutions for overcoming them by trial and error, but I never knew the Why to their cause. It seems strange after all these years of seeing inverted images through my scope to be told that they are really the right way up and that it is us that sees the world the wrong way. The mind boggles!

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