|Type||Diagonal (mm)||Width (mm)||Height (mm)||Area (mm2)|
|Standard 8mm film frame||5.94||4.8||3.5||16.8|
|Super 8 film frame||7.04||5.79||4.01||23.22|
|16mm film frame||12.7||10.26||7.49||76.85|
|Super16 film frame||14.54||12.52||7.41||92.8|
|2/3″ (The tube diameter!)
|1″ (The tube diameter!)
How to calculate a lens equivalent, made for a larger image size, on a smaller image size? Then we need the Crop Factor.
Please notice that the focal length (mm) of a lens designed for a specific format never changes when used in whatever other format, but the angle of view! The angle of view of a lens designed for a larger format decreased when used in a smaller format. Never use vice versa due to the covering issues!
Also, using a lens designed for a larger image area has an advantage like obtaining an image from the middle part of the lens since the diameter is larger, thus there will be no lens corner issues.
Crop Factor (CF) is calculated by dividing the larger image diagonal to the smaller image diagonal.
For example, we have a zoom lens designed for the 2/3″ TV camera tube format and want to use it on a Super 8 camera:
CF [2/3” diagonal / Super 8 diagonal] = [11 / 7.04 = 1.56], and 12.5mm X 1.56 = 19.5mm 75mm X 1.56 = 117mm.
So, a 12.5-75mm 2/3” format lens acts like 19.5-117mm Super 8 format lens, despite it is still a 12.5-75mm lens, due to the angle of view.
The lenses designed for 1″ cover the Regular/Normal 16mm and Super16 image areas safely. Also, the lenses designed for 2/3″ cover that image areas via third party optical converters having high quality optics, and they are highly expensive.
Note: The Bolex Reflex cameras require specially-designed RX lenses to compensate the extra flange focal distance added due to the thick prism pane. To be able to get proper results on a Bolex Reflex camera with a 3rd party C-mount lens, the iris openings must be set stopped-down past f/3.2 in order to eliminate the unwanted aberrations! Search for my post about that.