A Basic Explanation of the Z Mount by a Nikon Engineer

An interesting video.

 

Flange Distance and Mount Diameter Explained by a Lens Engineer

 

From the video, the 55mm diameter of the mount seems to be coupled to the 16mm flange distance. This would suggest it is not applicable to cameras with mirrors since it would be difficult to design a mirror system to fit in the small 16 mm vs. 46.5 mm F-mount flange distance. I suspect the F-mount will continue for many years to come.

?

 

Are you having a laugh?

Well, you certainly can't have a very short flange distance on a camera with a mirror in the space (although I've thought in the past that it might be possible to be a bit more compact than a traditional SLR with suitably funny optical paths in the finder).

 

Otherwise, it didn't seem hugely informative, I'm afraid. 55mm was chosen to be optimal because... I was hoping for something more specific than the goldilocks principle.

 

16mm seems to be as thin as Nikon could make the shutter and sensor cover (really? nothing to do with telecentricity?) which were thinned out specially. Which means a) that could explain the 1/200s sync limit, and b) "we made the sensor stack thinner" + "your old lenses work with no compromise" = I don't entirely believe them.

 

On the other hand, I'm going to call nonsense on the "big rear element means space for bigger AF motors" argument. I assume there must be a grain of truth, but not as presented.

 

It would also be nice if they said something about vignetting control with the wider rear elements, and possibly tilt shift. Given the 5-axis VR, I'm mildly curious to know the extent of the movement, given my previous statements about rear movements. Pentax have their star tracking mode, after all.

I guess what he meant is that if you have a lens with normal maximum aperture and moderate rear element size, with a large mount diameter setting the external diameter of the lens, you can put in a bigger motor in that space which is not used for optics (in the lens that doesn’t have an especially large rear element).

 

If they made the sensor optical stack thinner this should work great with older lenses. In any case, I am sure they did thorough testing.

I assume older lenses were designed to operate across the depth of a film (.14mm if you include the backing - that's 32 pixels at D850 resolution, so compare with the incident angle and you get a number which would restart a film vs digital argument which I don't want to do). Newer ones seem to have a particular stack depth in mind, according to lens rentals - though they were looking at the extra thick stack on micro 4/3, and Nikon don't seem to have been very consistent in the past (especially, I guess, with the transition to no lpf).

Oh, meant to say: I still don't see the "space for the motor" thing. Unless the motor has to fit physically inside the space of the lens mount, which I can't imagine has ever happened. Some day I must learn more about optics than the thin lens equation...

The mount outer diameter is the expected external diameter of the lens, and if the lens has a modest maximum aperture (small optical elements inside), there will be plenty of space for the motor within the outer barrel of the lens. If the mount had been smaller the motor would then introduce a bulge into the lens and make it thicker than expected for the mount. Of course if the lens has large focus group diameter then the bulge will appear nevertheless.

The mount outer diameter is the expected external diameter of the lens,

 

Why? The 50mm f/0.95 is clearly wider at the barrel. The mk2 70-200 f/2.8 F mount has a significant "swoop" out to a wider barrel shortly after the mount, where the tripod foot attaches. I don't see why the AF group has to be right inside the barrel.

 

Incidentally, looking at the 50mm f/0.95, it does look like the "configurable ring" is separate from the focus ring, as I first thought. The focus ring has distance marks engraved on it, so I assume the knurled thing at the back isn't just to make mounting the lens easier.

Why? The 50mm f/0.95 is clearly wider at the barrel. The mk2 70-200 f/2.8 F mount has a significant "swoop" out to a wider barrel shortly after the mount, where the tripod foot attaches. I don't see why the AF group has to be right inside the barrel.

 

I'm talking about normal lenses that regular people would use, such as the 35/1.8, 50/1.8, 24-70/4. The barrel is straight, no bulges. F mount has oversize lenses because it's narrow and old and expectations have changed over the decades.

 

Incidentally, looking at the 50mm f/0.95, it does look like the "configurable ring" is separate from the focus ring, as I first thought.

 

The Noct has a mechanical manual focus ring, not fly-by-wire as the other lenses, so it's not programmable, either.

I'm talking about normal lenses that regular people would use, such as the 35/1.8, 50/1.8, 24-70/4. The barrel is straight, no bulges. F mount has oversize lenses because it's narrow and old and expectations have changed over the decades.

 

I really hope that's not a design goal, because with the exception of something as bulky as the 24-70 f/2.8 VR, people tend not to care. The 50mm f/1.8 does seem to have a bit more of a bulge than the 35mm, for what it's worth - there's no big expansion after the mount, but it's not completely straight either. I'd be surprised if an 85mm f/1.8 was remotely straight.

 

The Noct has a mechanical manual focus ring, not fly-by-wire as the other lenses, so it's not programmable, either.

 

Oh, looking at the others, I see. I'm not sure I like that - I'd like more control points. Presumably Nikon could choose to make a long lens with multiple rings if they desired. I guess we'll see when they turn up. Oh well.