An Optical Engineer Explains Lens Flange Distance and Mount Diameter

Nikon has understandably made a big deal about launching their new Z-mount alongside the announcement of their new mirrorless cameras, the Z6 and Z...

Nikon has understandably made a big deal about launching their new Z-mount alongside the announcement of their new mirrorless cameras, the Z6 and Z7. The Nikon F-mount was originally released 59 years ago(!) and the company has made backward compatibility of the system a brand pillar.

But technology has changed dramatically over that time, and the release of the new system allowed Nikon engineers to effectively design a lens system without being hamstrung by history. Two key design features are a much shallower flange distance and a much larger mount diameter.

But what the heck does that mean? Nikon optical engineer and technical liason Atsushi Suzuki explains it all:

Here are some common mounts and their respective flange distances, which, in part, affect the depth of the camera body.

	Flange Distance
Nikon F-mount	46.5 mm
Nikon Z-mount	16 mm
Fuji X-mount	17.7 mm
Sony E-mount	18 mm
Leica L-mount	19 mm
Micro Four Thirds	19.25 mm
Hasselblad XCD mount	20 mm
Canon EF	44 mm

And here are common mount diameters that, in part, affect the light gathering capability:

	Mount inner diameter
Nikon F-mount	44 mm
Nikon Z-mount	55 mm
Fuji X-mount	44 mm
Sony E-mount	46.1 mm
Leica L-mount	48.8 mm
Micro Four Thirds	~38 mm
Hasselblad XCD mount	~61 mm
Canon EF	54 mm

I’m no engineer, but I suspect that the Z-mount’s shallow flange combined with a huge inner diameter made it relatively easy to design an F-mount converter like the Nikon FTZ. And in fact, it should make other lens adaptors possible as well.

Canon’s new mirrorless system is rumored for imminent release, and it will be interesting to see what types of design decisions they take to optimize size and performance.