Hi,about the following codes,I have some questions:

camera {
   location <10.0, 20.0, -100.0>
   angle 65
   right x*image_width/image_height
}

Question:The formula used is direction_length = 0.5 * right_length / tan(angle /
2) where right_length is the length of the right vector. How can I get the right
vector in this case or there is a default right vector?

camera {
   location <10.0, 20.0, -100.0>
   angle 65
   right x*image_width/image_height
   look_at <10.0, 20.0, 0.0>
}

Question:the help file says,"The look_at modifier changes both the up and right
vectors." And the direction_length calculation depends on the right vector.In
such a situation,how to compute the direction_length? And I think that the
direction vector is parallel to look_at vector,is it right?

Thank for your help!

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