Is flange focal distance of a camera system measured from the front edge of the lens mount to the film plane, or the back edge of the lens mount to the film
![optics - How can I increase the flange focal distance (back focal length) of DSLR lens? - Photography Stack Exchange optics - How can I increase the flange focal distance (back focal length) of DSLR lens? - Photography Stack Exchange](https://i.stack.imgur.com/jvzLX.png)
optics - How can I increase the flange focal distance (back focal length) of DSLR lens? - Photography Stack Exchange
![Another indirect attack at Sony: Canon explains why short flange distance and large mount diameter matters - mirrorlessrumors Another indirect attack at Sony: Canon explains why short flange distance and large mount diameter matters - mirrorlessrumors](https://www.mirrorlessrumors.com/wp-content/uploads/2018/12/24_o.jpg)