As from the POV help docs:The length of the direction vector determines the
distance of the viewing plane from the camera's location. A shorter
direction vector gives a wider view while a longer vector zooms in for
close-ups(which can be thought of as being similar to a real camera lens'
focal length - the longer the "direction" vector, the longer the focal
length, and the more "zoomed in" your image will be).  The longer the focal
length the smaller the angle of view.
  So,My question IS: How can we get such a image sequence that the focal
length of the perspective camera is fixed while the meantime it is moving
around in the scene? as In my mind,the camera moves,so the direction vector
varies,and the focal length would certainly varies,Is this true?

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jiangzhijun nous apporta ses lumieres en ce 2005-11-03 11:40:
> As from the POV help docs:The length of the direction vector determines the
> distance of the viewing plane from the camera's location. A shorter
> direction vector gives a wider view while a longer vector zooms in for
> close-ups(which can be thought of as being similar to a real camera lens'
> focal length - the longer the "direction" vector, the longer the focal
> length, and the more "zoomed in" your image will be).  The longer the focal
> length the smaller the angle of view.
>   So,My question IS: How can we get such a image sequence that the focal
> length of the perspective camera is fixed while the meantime it is moving
> around in the scene? as In my mind,the camera moves,so the direction vector
> varies,and the focal length would certainly varies,Is this true?
> 
> 
The order in whitch you define direction and look_at may cause unexpected changes. Set
direction, 
then set look_at. That way, the direction vector should be rotated acording to your
look_at.
Try using the angle keyword. It set the horizontal angle of view and, once set, don't
change if you 
move or rotate the camera.
If you use focal blur, the focal point won't move if you change the location of the
camera. I don't 
know how it react to changes in the look_at.
Using translate and rotate at the end of the camera definition will move that point
along with the 
camera. You completely define your camera at the origin and add rotate and translate
to orient and 
place the camera where you want it. Rotate after the translate will cause the camera
to move in 
circles around the origin.

-- 
Alain
-------------------------------------------------
Gone crazy, be back later, leave message.

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