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kdworld

OpenGL setting Focal Length in Opengl

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Helloo Good people, I am bit confused about the focal length parameter in perspective projection. since opengl has no real lens , what is mean by focal length ? My assumption is , focal length is the distance to near plane from camera orgin. And increasing the focal length will increase the image size.. Any api exists to set focal length ? ( if it is near plane distance i tried with gluPerspective's near distance parameter, but no change happens in screen). Please correct me if you know . Thanks in advacne. kdworld If you can Dream, You can Do it

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Check out the two first figures in this section of the Red Book, figure 3-13 and 3-14. They show you the relationship between the view volume and the near clip plane.

The difference between the two is that in the first figure (related to glFrustum) you have a fixed clip plane size, while in the second (related to gluPerspective) you have a fixed field of view. The difference is that when the plane is of a fixed size, the FOV will change as you move the clip plane further of closer, changing the perspective. With a fixed FOV, the clip plane size is calculated and the perspective is not changed.

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Thanks for the reply.

So what i understodd is , when using gluPerspective FOV is never changed. and the clip near plane is calculated. from angle and near distance . right ?

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