> Hi
> 
> I have figured out a little macro to autocenter an object (see below),
> but I would like to auto scale that object to fill x% of the image x
> and y dimensions.
> 
> 
> I know of image_height and _width and I suspect that the calculation I
> need has something to do with the camera angle and other camera
> params, but I am not sure how to proceed. Also, I would like this to
> work for a perspective camera and an orthographic camera.
> 
> I would appreciate some help, thanks

Orthographic camera: the image scope is given by the right and up 
vector's length. 

 up 1*y
 right 1*x

give a 1x1 scene size, stretched over image_height and _width.

Perspective camera: have faith in the maths, for not so narrow angle, you 
have a distortion near the border: a circle is not a circle anymore!

Best hint from me: Use the source for the camera ray computation and 
reverse the math for some fixed %, assuming a central position of the 
object. Or do it the caltech way...

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