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
![Back focal length for a thick lens between two different optical media. | Download Scientific Diagram Back focal length for a thick lens between two different optical media. | Download Scientific Diagram](https://www.researchgate.net/publication/355037895/figure/fig4/AS:1076014637686784@1633553289385/Back-focal-length-for-a-thick-lens-between-two-different-optical-media.png)
Back focal length for a thick lens between two different optical media. | Download Scientific Diagram
![Universal method for determining the focal length of optical systems by moire deflectometry. | Semantic Scholar Universal method for determining the focal length of optical systems by moire deflectometry. | Semantic Scholar](https://d3i71xaburhd42.cloudfront.net/3efb95681f7b4958d98e3d97ad26c940fc532203/2-Figure2-1.png)
Universal method for determining the focal length of optical systems by moire deflectometry. | Semantic Scholar
![Focal length, focal distance, dioptric power, curved mirror, lens equation, microscope, photographic objective, focus, beam radius Focal length, focal distance, dioptric power, curved mirror, lens equation, microscope, photographic objective, focus, beam radius](https://www.rp-photonics.com/img/focal_length.png)
Focal length, focal distance, dioptric power, curved mirror, lens equation, microscope, photographic objective, focus, beam radius
![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)