Camera Lens Mounts Explained: DSLR, Mirrorless, Cinema, and Medium Format
Introduction
A lens mount is the mechanical and electronic interface connecting a lens to a camera body. It sets the physical connection, the communication protocol for autofocus and aperture control where applicable, and, most importantly for anyone adapting lenses, the flange focal distance, the exact distance from the mount’s flange to the sensor plane. Every spec sheet detail about compatibility ultimately traces back to that one number.
Photography, cinema, and medium format systems have each evolved their own mount families, built around different priorities: photography mounts favor fast electronic autofocus communication, cinema mounts favor mechanical reliability and interchangeability across a huge range of specialty lenses, and medium format mounts prioritize sensor size and image quality over speed.
1. Photography Mounts
DSLR mounts like Canon’s EF, Nikon’s F, and Pentax’s K were built around a mirror box and, in most cases, a mechanical or hybrid mechanical/electronic aperture linkage. Nikon’s F mount has been in continuous use since 1959 and Pentax’s K mount since 1975, which is why decades-old manual lenses still physically mount on current bodies from both brands, even if not every feature works. Canon’s EF mount, launched in 1987, went fully electronic and became the dominant DSLR mount for over three decades.
Mirrorless mounts like Sony’s E/FE, Canon’s RF, Nikon’s Z, Fujifilm’s X, the L-mount alliance (Panasonic, Leica, Sigma), and Micro Four Thirds (Panasonic, OM System) drop the mirror box entirely and communicate with lenses purely electronically: autofocus motors, aperture control, image stabilization data, and lens correction profiles all pass through electrical contacts. Without a mirror box to clear, these mounts also have much shorter flange focal distances than the DSLR mounts they replaced, which is part of why mirrorless bodies can adapt older DSLR glass but not the reverse.
These mounts prioritize fast, reliable autofocus tracking and compact bodies, which is exactly what stills and run-and-gun video shooters need most.
2. Cinema Mounts: PL and Beyond
The PL mount, positive lock, is the closest thing cinema has to a universal standard. It’s a purely mechanical mount: a bayonet ring with a locking collar and no electronic contacts at all, which is precisely why it has remained stable and interchangeable across decades of cinema lens designs from Zeiss, Cooke, ARRI, Angenieux, and dozens of other manufacturers. Focus, iris, and zoom are all controlled externally through gears and follow-focus systems rather than through the mount itself, so there’s nothing to go out of sync between a lens built in 1985 and a camera built last year.
Larger-sensor cinema cameras have introduced their own extended mounts, like LPL, designed for full-frame and larger coverage, alongside legacy mounts like PV used on some older Panavision systems. All of them still lean on the same philosophy: mechanical reliability over electronic convenience. Beyond these, broadcast, Panavision’s large-format SP70, and the increasingly capable Canon RF, Nikon Z, Sony VENICE, and Fujifilm G-mount cinema systems round out the field — for the full breakdown, see our companion guide, Cinematography Lens Mounts Explained.
3. Medium Format Mounts
Medium format systems use a larger sensor or film area than full-frame, roughly 43.8 x 32.9mm on current digital backs, all the way up to a true 6x7cm frame on film. That extra sensor area buys more resolution and shallower depth of field at a given aperture, at the cost of speed, size, and price.
Fujifilm’s G-mount (GFX series) and Hasselblad’s X-mount (XCD lenses, X1D/X2D/907X) are the two current mirrorless medium format mounts, both launched in 2016 and both built around roughly the same 44x33mm sensor size. Hasselblad’s X-mount has a notably shorter flange focal distance, 18.14mm versus Fuji’s 26.7mm, which makes it easier to adapt other glass onto.
Pentax’s 645 mount, dating back to 1984, is the last mirror-based medium format mount still in production, used on the 645Z DSLR-style body. Phase One’s mount, built on the Mamiya 645AFD standard from 1999, powers the XF camera system and its IQ digital backs, which scale up to true 645 film-frame sensor sizes on the highest-resolution backs.
Mamiya’s own RB67 and RZ67 systems, introduced in 1970 and 1982, take a different approach entirely: a rotating back for portrait or landscape shooting without turning the camera, interchangeable film backs for swapping stock mid-roll, and a leaf shutter built into every lens rather than a focal-plane shutter in the body.
4. Flange Focal Distance and Adapters
Adapting a lens from one mount to another only works cleanly in one direction: from a longer flange focal distance to a shorter one, with a passive spacer adapter, or from a shorter to a longer distance using an adapter with corrective optics inside it, since simple spacers can’t add negative distance. This is why PL lenses, with a relatively long flange focal distance, adapt easily onto most mirrorless cinema cameras, while going the other way around generally requires an adapter with built-in glass, which can affect image quality.
Rental houses and camera assistants live and die by this chart in practice, since a wrong assumption about flange distance means a lens that either won’t reach infinity focus or won’t mount at all. Even a correctly matched mount can drift out of spec over time — see our guide on what happens when flange distance is wrong, and how shimming fixes it.
Common Mounts at a Glance
| Mount | Type | Flange Focal Distance | Common Use |
|---|---|---|---|
| PL | Mechanical | 52.00mm | Cinema |
| EF | Electronic | 44.00mm | Canon DSLR |
| F | Mechanical/Electronic | 46.50mm | Nikon DSLR |
| K | Mechanical/Electronic | 45.46mm | Pentax DSLR |
| RF | Electronic | 20.00mm | Canon mirrorless |
| Z | Electronic | 16.00mm | Nikon mirrorless |
| E-mount | Electronic | 18.00mm | Sony mirrorless |
| X-mount | Electronic | 17.70mm | Fujifilm APS-C mirrorless |
| MFT | Electronic | 19.25mm | Micro Four Thirds |
| L-mount | Electronic | 20.00mm | Panasonic, Leica, Sigma |
| G-mount | Electronic | 26.70mm | Fujifilm GFX medium format |
| Hasselblad X | Electronic | 18.14mm | Hasselblad medium format |
| Pentax 645 | Electronic | 70.87mm | Pentax medium format |
| Phase One | Electronic | — | Phase One / Mamiya 645AFD medium format |
Conclusion
Lens mounts split into a few clear philosophies: electronic and compact for photography and hybrid mirrorless work, purely mechanical and built for decades of interchangeability in cinema, and large-sensor and image-quality-focused in medium format. Understanding flange focal distance is what actually determines whether an adapter will work, and it’s the single most useful number to know before buying glass for a system you don’t already shoot on.