The term “flange distance” describes the separation between a camera’s lens mount and the focal plane of its sensor or film. It is the distance, when the lens is mounted and focused to infinity, between the mounting flange on the camera body and the film or sensor plane.
The minimal distance that must exist between the lens and the sensor in order for the lens to properly focus is known as the flange distance, which is a crucial standard for camera manufacturers. For lenses to focus properly and create sharp images, this distance is essential. The lens may not be able to focus on infinity or it may focus outside of the sensor plane if the flange distance is off, producing fuzzy or out-of-focus photos.
This distance is crucial when switching lenses between different camera systems. There are adapters available to enable the use of lenses from one camera system on another camera body, but in order for the lens to focus correctly, the adapter must be able to match the flange distance of the lens and the camera body. The lens may not be able to focus at all or be able to focus to infinity if the distance is incorrect.
The construction of the camera body and lens mount determines the flange distance of a camera. It differs across different camera systems and even between models of the same system. For instance, a Canon EF mount’s flange distance is 44mm, while for a Nikon F mount it is 46.5mm.
The flange distance can be measured from the lens mount to the film plane in film cameras, in addition to the more common measurement from the lens mount to the sensor plane. The flange distance is measured to the actual focal plane in some cameras where the sensor or film plane may not be at the same distance as the mounting flange.
As lenses are adapted to various camera systems, the flange distance can have an impact on how well they work. For instance, mounting a lens too far from the sensor may come from adapting it to a camera with a shorter flange distance. This may affect the lens’s ability to focus and the quality of the images produced. In general, it is easier to adapt a lens with a shorter flange distance to a camera with a larger flange distance since the lens can be placed more closely to the sensor.
Compared to conventional DSLRs, some camera systems, such mirrorless cameras, offer lower flange lengths. This makes it possible to employ adapters that can mount lenses from various systems without the need for extra optics or adjusting the lens’ flange distance. However, image quality and performance may be impacted by adapters that alter the flange distance or need for extra lenses.