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Thread: A Noob's questions about optics (1)

  1. #1 A Noob's questions about optics (1) 
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    Good day everyone, i not long ago join this forum as a result of my enthusiasm on science, and for asking things that my familiar teachers had not given satisfying answers for them before. these are several of my questions :

    1. Why is our focus of sight limited to some degree? (similarly : why can't we see bacterias with our naked eye, or why can't we see the details inside moon craters?)

    2. Does the deeper our focus of sight be, the more limited our area of sight? (similarly : will we see more narrowly if we DO can see bacterias?, or will our area of sight be very limited if we can see the details inside lunar craters?)

    3. What does our two-eyed system contribute to our sight?

    4. What is the difference between 3D view and 2D view, in detail? (got this idea from the current entertainment trend)

    5. Does anyone know why light sources sometimes produce "star"-shaped impression ? (ex : stars, shiny teeth, shiny bald heads, lightbulbs, mirror reflections)

    that's all for now, thanks for replying.


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    Quote Originally Posted by TheAccursed View Post
    Good day everyone, i not long ago join this forum as a result of my enthusiasm on science, and for asking things that my familiar teachers had not given satisfying answers for them before. these are several of my questions :

    1. Why is our focus of sight limited to some degree? (similarly : why can't we see bacterias with our naked eye, or why can't we see the details inside moon craters?)
    The human eye has only one lens. The lens is adapted to the shape and curvature that best enables us to see clearly at our scale.

    Quote Originally Posted by TheAccursed View Post
    2. Does the deeper our focus of sight be, the more limited our area of sight? (similarly : will we see more narrowly if we DO can see bacterias?, or will our area of sight be very limited if we can see the details inside lunar craters?)
    Yes. I can imagine an alien being that evolved a series of multi-lensed eyes possibly being able to see in a far less narrow range than ours.

    Quote Originally Posted by TheAccursed View Post
    3. What does our two-eyed system contribute to our sight?
    Depth perception.

    Quote Originally Posted by TheAccursed View Post
    4. What is the difference between 3D view and 2D view, in detail? (got this idea from the current entertainment trend)
    Perspective. That is to say, an oblong shape viewed straight on in 2D will have the same perspective across the image. A 3D view of the same object, however, will have 'depth' meaning that the perspective of the furthest point will be altered by the distance, unlike 2D where it would have the same dimensions as the closest point.

    Quote Originally Posted by TheAccursed View Post
    5. Does anyone know why light sources sometimes produce "star"-shaped impression ? (ex : stars, shiny teeth, shiny bald heads, lightbulbs, mirror reflections)
    I have a guess on this one that relates to the above- But I'd rather not guess at the moment, when someone else may have an exact answer.


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    reply to neverfly : what excactly does it take to form a 3D view? (more than 1 eye, specific shape of the object, specific distance from the object, etc),
    and can you explain more about "the alteration of the furthest point by distance" that you said? hnx for replying.
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    Quote Originally Posted by TheAccursed View Post
    reply to neverfly : what excactly does it take to form a 3D view? (more than 1 eye, specific shape of the object, specific distance from the object, etc),
    At our scale- distance isn't as important.
    At least two eyes or two cameras, for that matter.
    This is binocular vision.
    Binocular vision - Wikipedia, the free encyclopedia

    Quote Originally Posted by TheAccursed View Post
    and can you explain more about "the alteration of the furthest point by distance" that you said? hnx for replying.
    Well, this much you already know:
    The further away an object is, the smaller it appears. Your friend waving at you from half a mile away looks, from your perspective, like he could fit in the palm of your hand.

    This is true for solid objects, as well. For big objects, it's apparent. Such as a building. One end of the building looks smaller than the end of the building that is closest to you.
    Such as here:
    http://detroit1701.org/Graphics/Garfield%20Building.jpg

    Also, look at this building, not because it's a good example of perspective but because it's a very cool looking structure...
    http://upload.wikimedia.org/wikipedi...y_building.jpg

    This is true for all the scales we can see with our eyes. A bus.
    A car.
    The more distant part or side of a slid object will still obey perspective.
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    At our scale- distance isn't as important.
    than can you tell me at what scale does that become significant?, and does a specific shape become necessary for the effect ot occur?

    At least two eyes or two cameras, for that matter.
    what would the perspective be if we have more than two eyes?

    The further away an object is, the smaller it appears. Your friend waving at you from half a mile away looks, from your perspective, like he could fit in the palm of your hand.
    can you or someone else please explain the cause of this "alteration of scale"?, can 2D view cause this also?
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    Quote Originally Posted by TheAccursed View Post
    than can you tell me at what scale does that become significant?, and does a specific shape become necessary for the effect ot occur?
    It becomes utterly insignificant at the quantum scale, I suppose...
    Quote Originally Posted by TheAccursed View Post
    what would the perspective be if we have more than two eyes?
    Confusing.
    Quote Originally Posted by TheAccursed View Post
    can you or someone else please explain the cause of this "alteration of scale"?, can 2D view cause this also?
    I tried to.

    And did you read the link I posted?
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    ok, i'm now starting to get it
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    For your last question. these stars come from the diaframe. It is a hexagonal piece that limits the amount of light shining through. It however create wave fronts perpendicular to its edges. Hence, it looks like a star. It is an engineering downside.
    Neverfly likes this.
    In the information age ignorance is a choice.
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    Quote Originally Posted by TheAccursed View Post
    Good day everyone, i not long ago join this forum as a result of my enthusiasm on science, and for asking things that my familiar teachers had not given satisfying answers for them before. these are several of my questions :

    1. Why is our focus of sight limited to some degree? (similarly : why can't we see bacterias with our naked eye, or why can't we see the details inside moon craters?)
    This is a matter of optical resolution. For a single lens, this is determined by something called the "numerical aperture". If you draw 2 lines from the point being looked at, one through the center of the lens and the other to the outer edge of the lens, and then take the Sine of the angle formed, you get the numerical aperture. The larger the numerical aperture, the smaller the object your eye can resolve as a distinct point.

    For distant objects, like the Moon, the angle is very small and thus the limits of resolution are large. Objects, like the details of craters, have to be very large in order for use to resolve them as separate objects. The lenses of our eyes are just too small for us to see fine detail at this distance. This is one reason (the other being light gathering), that large aperture telescopes are better, the larger aperture gives a larger NA for the same distance for the object viewed.

    When things get closer, the numerical aperture gets larger and we can see smaller detail. However, for objects as small as bacteria the NA has to be quite large making the distance between lens and bacteria very small. Our lens is a jelly like blob which is pushed and pulled into shape in order to focus. There are limits to how much it can be shaped and thus limits to how close an object it can focus on. (This is something that decreases with age and can eventually lead to farsightedness).

    Even if the lens could be forced into the right shape, it would have to more spherical. As lenses get thicker, they experience more spherical aberration, meaning they lose the ability to focus on a single point and the focus is blurred. Microscopes get around this by using compound lenses, or a series of lenses that the light passes through rather than just a single lens.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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