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Focal point purpose

  1. Dec 15, 2012 #1
    What is a purpose of focal point in optics,especially in human eye?
    I don t understand,why is required to make a focal point in retina?Everywhere in articles are pictures of this problem clarified by one principle:Object,which we see reflects rays in all directions,and those which are parallel goes to focal point.For example we have vector,which is parallel with our eye.Top of the vector is for example A point,and bottom of vector is B point.And now,here comes my problem.If ray from point A goes parallel to our eye,and rays from point B goes parallel to our eyes,these two points meet in one focal point.But what see our eye then?Instead of two points only one point?I know,there are a rays which are not parallel and goes in other directions and iluminate our retina in other places.But then,why we need the focal point?
    My question in brief:1.When all parallel rays from different places of our vector goes to one point,what we see?
    2.If other rays,which are not parallel make image complete,why we need to have focal point on our retina?Subsequently,it is enough just to catch all parallel rays from all points on our vector on our retina,and we have a image.
    THanks for clarifying......a lot
  2. jcsd
  3. Dec 15, 2012 #2


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    Staff: Mentor

    Focusing causes rays emanating from a point on an object to form a corresponding point on your retina. So printed on your retina is formed a shape similar to that which the light comes from (albeit inverted). Otherwise, with all rays hitting higgledepiggledly you would see a blurr, like being inside a cloud or fog.
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