Introduced in 1950, this side-mounted, parallax correcting viewfinder gives a field of view for lenses of 8 different focal lengths. Field marking numbers are visible through the viewfinder, as well as engraved on the dial. Later models were fitted with an external prism for focal lengths of 10mm or 5.5mm.
An octameter will not fit on the film door of earlier model H cameras unless the mounts have been modified to accept it. Two versions were available: (VICON) For the H-16 with focal lengths of 16mm, 25mm, 35mm, 50mm, 63mm, 75mm, 100mm and 150mm; (VIHUI) For the H-8 with focal lengths of 6.5mm, 9mm, 12.5mm, 25mm, 36mm, 50mm, 63mm and 75mm.
Eye Level Focus
This updated version appeared in 1949, but became standard equipment on H-8/H-16 Deluxe and Standard models in 1950. It enables critical focusing of lenses in the top position to be done at eye level from the rear of the camera. Unlike the previous version, this one allows the user to adjust for his or her eyesight. Originally $43.41 US with tax included, according to a September, 1950 retail price list.
PC-12 Preview Finder
Manufactured in 1958 for the T and M series cameras, the PC-12 is a parallax correcting preview finder with viewing fields for lenses of four different focal lengths. Although less versatile than the octameter, it was introduced for current and potential Bolex owners who desired a viewfinder that changed focal lengths with faster speed. 
Two versions were available: For the H-16 with focal lengths of 16mm, 25mm, 50mm and 75mm; For the H-8 with focal lengths of 6.5mm, 12.5mm, 25mm and 36mm.
1 "Three New H-Cameras," Bolex Reporter, Fall 1958, 8.
Pictured to the right is the original prismatic focuser (CADRO) introduced in the 1940s. In 1954, the model H camera was redesigned with, among other things, a new pressure pad and gate assembly. The Prismatic Focuser, therefore, had to be redesigned to allow proper focusing through the gate.
Pictured to the left is the later model (CADIL) used on H-16 cameras with a serial number higher than 100,401 and on H-8 cameras with a serial number higher than 97801. Older cameras below these numbers required the original CADRO. The function remained the same: as an aid in critical focusing through the taking lens and only before film was loaded into the camera.