The back focal distance, often referred to as the back focal length or simply BFD, is a critical parameter in scientific and industrial cameras. It defines the distance between the last optical element (usually the rear lens or the image sensor) in the camera lens system and the image plane or sensor surface.

By adjusting the distance between the last optical element and the image sensor, we can control the focus of the camera. This is crucial for achieving sharp and clear images, especially in applications where precision is essential. The back focal distance, in combination with other optical parameters like the lens focal length, determines the magnification of the camera system. Adjusting the BFD can impact the size and scale of the objects being imaged.