The other interesting thing about Hitchcock’s “Rear Window” is the fact that the binocular shots, and the camera shots appear the same. Again we could mark this down to artistic license, but there are inherently some issues which persist from an optical point-of-view. Firstly, what kind of binoculars are they? Little is written in the literature about the brand, so that requires a little investigative work.
The most telling feature of these binoculars is that these are porro prism binoculars. In Porro prism Binoculars the objective or front lens is offset from the eyepiece. This offset is often characterized by a cap, which terminates the transition from ocular to objective lens.
With some manufacturers, the transition seems to be smooth, with streamlined curves. There are a couple of brands that stand out in this respect: Bausch and Lomb (USA), Bushnell (USA), Cadillac (USA, made in Japan). Brands like Zeiss on the other hand, had a capped, “hard” transition.
Beyond this, it is hard to tell what brand they were, because those markings would be on the front of the binoculars. More important are likely the power of magnification (how many times closer you are to the thing you are viewing), and the objective diameter of the lens. After doing some comparative measurements of the binoculars in the movie, with those in a early 1950s Bausch and Lomb catalog, I would guesstimate that these are the 7×50 binoculars, i.e. objective diameter was 50mm, and the power of magnification 7 times. A 400mm lens has a magnification factor of ×8, so binoculars with a power of ×7-8 would make sense (if we ignore the optical differences between binoculars and 35mm film lenses, e.g. cameras have a film plane, binoculars don’t).
The other factor which makes the B&L 7×50 the most likely candidate is that Bausch and Lomb supplied the US armed forces during WW2 (and Jeff was in the US Army Air Force), and this particular model was the Navy model, which had the “highest relative brightness of any binocular”, a so-called true “night glass”. So what are the issues between the 400mm camera lens and the binocular optics, assuming 7×50?
- Field-of-View – The FoV of a 400mm lens is just over 5° (horizontal), which at 100′ distance (the width of the courtyard), translates to around 9 feet. The B&L 7×50 binoculars had a linear field of 381′ at 1000 yards, which would be about 12.7′ at 100′.
- Full image circle – The camera would truncate the image circle of the lens to a rectangle, and therefore the maximum FoV is only possible along the diagonal of the frame. Binoculars allow you to see the full circle of the FoV and thus the maximum FoV in all directions. A 35mm camera with a 3:2 ratio only displays about 59% of an image circle with the same diameter as the diagonal of the rectangular image sensor.
- Stereo Vision – Binoculars allow both eyes to see slightly different angles of the same objects that allow use of depth perception. Other than specialized 3D cameras, most cameras are monocular.
So Hitchcock’s use of both binoculars and a 35mm camera with a 400mm lens does take a lot of artistic license, because they are not the same, but portray the same thing on screen.