The earliest model H cameras included this viewfinder which could be fitted at the top or on the side of the camera. The field of view is shown for lenses of 3 focal lengths. Field of view is changed by raising or lowering side levers which move magnifying prisms into place inside the viewer. When fitted to the side of the film door, the finder offers parallax correction by adjusting a dial which corresponds to the distance between the subject and lens. The H-16 version shows the angle of view for 15mm, 25mm and 75mm lenses; the H-8 version adjusts for 6.5, 12.5 and 35mm. A serial number is located on the rear of the viewfinder which, in most cases, matches the serial number of the camera to which it is attached.
At first glace, one might mistake this for a tri-focal viewfinder. This item, however, contained prisms to correct parallax, and to adjust the field of view, for lenses of 100mm and 150mm focal length. The illustration above shows a fixed 150mm focal length. However, the only one I've come across had levers to adjust for both 100mm and 150mm. In September of 1941, this accessory sold for $37.50 US.
Bolex Angle Viewer
This device used a spring-indented collar to fit over the Trifocal finder. It deflected the angle of view sideways at a 90 degree angle to the camera axis. The purpose was to allow the movie-maker to be less conspicuous. It sold for $8.63 US, in 1949.
A coupled rangefinder manufactured by the American Bolex company. This was meant for use exclusively on the H-16 with a Kern Switar 25mm f/1.4 as the taking lens. The device attached to the top position lens mount and coupled to the lens. Focusing was done by turning the focus ring until the image aligned in the viewfinder. The price in 1947, including tax: $43.50 US
The prismatic focuser was inserted into the film gate, and allowed focusing at the film plane through the taking lens. Although useful for cinemicrophotography, animation and title work, its use is rather limited for normal filming as the film door and pressure pad are removed while focusing. The model shown here is compatible with Bolex H-16 cameras having a serial number lower than 100,401, or H-8 cameras lower than 97,801.
Auxiliary Focus Tube
Although the manufacturer is unknown, this critical focus device was advertised as early as 1940 in American Bolex catalogs at a price of $45 US. Attached to the top of Bolex H models, it diverts the image on the critical focus screen by 90 degrees, allowing focusing to be done at eye level rather than straight down.
Eye-level focuser (early)
This is an early version of the Bolex Eye-Level Focuser, introduced in late 1948 or early 1949. It was included on H-16 and H-8 cameras at no additional cost when first introduced, but could be bought separately for $43.41 tax included in 1949.