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OT but flange focal distance is overmystified. It's just a mechanical interfacing spec. You can't drill a hole on the sensor and mount lens body on it, and len
by numpad0 2y ago
OT but flange focal distance is overmystified. It's just a mechanical interfacing spec.
You can't drill a hole on the sensor and mount lens body on it, and lenses must be placed at exactly focal distance away for parallel beams to converge on film or farther for diverging beam(from non-infinitely-far objects), so body designers pass a distance measurement from film to a known feature(mounting ring top surface) to be able to design a lens barrel. That's the flange-focal distance, sort of a "design length of body" to subtract from your overall lens barrel length.
It's actually possible to drill a hole on the PCB and woodscrewing lens directly on in cases with webcams and CCTV cameras, and in those cases the distance is 0.
- avidiax 2y agoFor the case of 35mm SLRs, Nikon/Canon/Pentax etc. all have 45mm flange distances, give or take a couple of millimeters. That's basically the minimum to have room to swing the mirror and for a couple of shutter curtains. So all of them having completely incompatible mounts is because they wanted to compete based on lock-in to a complete system, rather than compete for bodies and lenses separately. Even worse, the fact that their flange distances are all within a couple of mm makes passive adapters impossible, since just the bayonet part of the mount is longer than that.
- hcarvalhoalves 2y agoThe Pentax followed the distance of the M42, which was pretty much an open standard by then, and many manufacturers at the time released lenses in K bayonet. The other camera makers diverged from the standard.