I've tried to do a simple diagram to illustrate what's happening. On the left the two frames are 4x3 and 3x4 ratio with the longest side the same length for each. On the right we see the effect of fitting the vertical frame into the same size viewport as you would have for the default horizontal frame. It's not that the size of the object has changed relative to the frame, but that the size of the frame has changed. (It's more of a scaling rather than a zoom) So if you render the same scene at the same focal length with the same longest length, the objects in your scene (those visible in both aspects) will be the same size. Not sure if this makes things any clearer. But the way I see it focal length controls the "physical" aspects of the camera (such as perspective) while the size of the viewport (or render) controls the scaling of the image (like blowing up a photo to a larger size) -- Mark

Mark