# Projection : gluPerspective

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The fov parameter that specify y axis to user.Well when Im trying to use it. When I put 10.0f into fov parameter, The result of the image show more bigger but if I put 100.0f the Image shot more little.Hmm.. So I dont understand about fov .. First time I thought that fov specify how user eye wide but Im wrong.. I think if large number of fov large image will appear.So I think fov enlarge image and decrease image size.. Am I right?? or Im wrong ... if I am wrong please give me some advise.. sry for asking noob one but Im just a kid.

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The field-of-view parameter (fov) is typically the vertical field of the view of the eye. This is a little tricky to explain without a diagram, but basically smaller field of view means that the view plane you are projecting onto is smaller; the area it covers is smaller, so you see less of the scene.

If your scene consisted of a cube, for example, with a larger field of view you might be able to see beyond the edges of the cube. With a small one, you might only be able to see the front face of the cube. Here's some crude ASCII art:

   Large FOV                          Small FOV---------------                    ---------------       /        /   +--+                     __  +--+     /    |  |                  __     |  |eye      |  |            eye < __     |  |    \    +--+                     __  +--+     \

However, your viewPORT is likely the exact same size, so the reduced area of the scene that you see still occupies the same area on your actual screen (it gets scaled up). This is why you get a "zooming in" effect when you decrease the field-of-view.

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Quote:
 First time I thought that fov specify how user eye wide

That's not wrong, field-of-vision is like the maximum angle that the user eye can see sideways...

If you specify a large fov then you'll see much more.. but as the viewport (the screen) has a fixed size the objects will appear smaller so that they fit in your view

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