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A note of mental ray/iray camera terminology.

The original mental ray camera is a pinhole camera. Therefore, some of the terminology differs with a normal camera. I will write them down here. aperture: This is the film width size. This has no relationship with lens aperture/opening. mental ray's camera was a pinhole camera, there is no lens aperture. focal: This is the distance from lens to the film (sensor). Pinhole camera always focused, so there is no focal length meaning. But using parameters aperture and focal length, we can compute the horizontal field of view. I think these two parameters exist for this purpose. aspect ratio: This is film(sensor)'s aspect ratio. There is no relationship with pixel resolution and camera geometry.  aspect ratio = film width/film height. Note: If we use aperture, focal, and aspect ratio, we can compute the vertical field of view. mental ray/iray camera model (pinhole camera) without lens shader Current mental ray/iray can have depth of field effect, etc., this termino