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
![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
![15: Lens L1 and L2 is beam expander. L1 has a front focal length FFL of... | Download Scientific Diagram 15: Lens L1 and L2 is beam expander. L1 has a front focal length FFL of... | Download Scientific Diagram](https://www.researchgate.net/publication/269706704/figure/fig18/AS:652580606734354@1532598749430/Lens-L1-and-L2-is-beam-expander-L1-has-a-front-focal-length-FFL-of-125mm-and-back.png)
15: Lens L1 and L2 is beam expander. L1 has a front focal length FFL of... | Download Scientific Diagram
![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)