Mono-lens stereo beam splitter
Aperture vs field diaphragm/mask
- TOP: all the light rays coming from one point though the lens, supposed point A, is sent to a single point of the picture (when focused).
- MIDDLE: if you have a diaphragm/mask very very close to the lens (ideally inside the lens system), you are reducing the light rays, keeping the whole scene with less light. You have an aperture diaphragm/mask.
- BOTTOM: if your diaphragm/mask is far from the lens (according to its size), you simply hide all the light of a part of the scene (suppose you are hiding all the light from point A), keeping the light of the other part of the scene (suppose point B). You have a field diaphragm/mask.
To be able to do stereo shots, you need your mirrors to act like 2 complementary field masks, thus being not-to-close to the lens.
Diaphragm included in a lens system:
