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
![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
![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)