The difference between back focus and flange back?

Q: What is back focus


A: Back focus refers to the distance from the rear end of the lens to the focal plane (the imaging sensor of the camera).


If the back focus is misaligned, it will result in a focus shift.


Q: What is flange back?



A: Flange back refers to the distance from the lens mount’s mounting surface to the imaging sensor.



There can be confusion between flange back and back focus, but they are distinct concepts.

The distance from the camera’s C-mount to the imaging sensor surface (flange back) may vary slightly depending on the camera. Therefore, when changing lenses or cameras, it may be necessary to adjust the back focus.
(We ship products that combine cameras and lenses with precise adjustments.)
Additionally, for lenses with a back focus adjustment mechanism, customers can also make fine adjustments themselves.

We also offer lenses with a back focus adjustment mechanism as optional accessories.



Back focus mechanism lens SDS-M19

For detailed product information, please contact our technical support.