Lens: Does a large mounting diameter really allow design advantages for large aperture lenses?

First: Sony not necessarily disagree with the Nikon claim. It's just that Sony designed his mount & # 39; E & # 39; with a throat diameter of 46.1 millimeters at a time when it looked like it would be an APS-C mount only for the compact NEX series ILC without a mirror.

Later, Sony made the decision to move to full-frame territory using the support & # 39; E & # 39; totally electronic, instead of using the support & # 39; A & # 39; existing mechanic that went back up to the Minolta movie cameras or create another new support for your FF cameras without a mirror. Throat diameter of 46.1 mm from the mount & # 39; E & # 39; it is large enough to accommodate the 43.27 mm diagonal of a 36×24 mm FF sensor.

Second: the electronic mount "EOS" of the Canon EOS, introduced in 1987, has a throat diameter of 54 mm. The existence of a 50mm f / 1.2 lens in the Canon EF mount with its 54mm throat diameter does not refute Nikon's claim that its new 55mm wide "Z" frame allows for better design of the lens than its previous "F" mount, which had a narrow throat with a diameter of only 44 mm.

Basically, since 1987, when Canon introduced the mount & # 39; EF & # 39; with a recording distance of 44 mm and a throat diameter of 54 mm, Nikon has been technically limited by matching some of Canon's lens designs due to its own recording distance of 46.5 mm and throat diameter of 44 mm narrower. .² Similarly, with the introduction of support & # 39; E & # 39; from Sony in 2010 and its application to the FF cameras with the introduction of the Sony α7 camera series at the end of 2013, the Nikon & # 39; F & # 39; (and Canon EOS cameras were also at a disadvantage with respect to the design of very wide-angle and wide-angle lenses that can take advantage of the short recording distance to simplify design, reduce size / weight and adjust or improve lens performance in a smaller package.

Nikon is promoting the new throat diameter and a much shorter recording distance of the support & # 39; Z & # 39; because it is a millimeter wider than the Canon EF stand that was introduced in 1987 and two millimeters shorter than the stand & # 39; E & # 39; from Sony. in 2010. It is also 11mm wider and 30.5mm shorter than its own support & # 39; F & # 39 ;.

For shorter focal length lenses with wider openings, a larger throat diameter allows larger exit pupils. A shorter recording distance allows shorter focal lengths without resorting to a complex retrofocus design to make lenses with focal lengths shorter than the recording distance. Both factors combined mean that the larger rear lens elements can be placed closer to the image sensor. This allows for lens designs that are not possible using narrower throat diameters placed at greater distances from the image plane of the camera.

Control lens. 85mm f / 1.0

With an 85mm focal length lens, the difference between the recording distance of 16mm and 46.5mm is not really a factor at all, since 85mm is considerably longer than the recording distance of 46.5 mm of the Nikon "F" mount. When you look, for example, at 85mm lenses for Sony E-bracket and compare them with 85mm lenses with the same maximum aperture for Canon EF support or Nikon F mount, it is quite easy to see that the lenses are about 30 millimeters longer for the mount & # 39; E & # 39; compensate the mounting flange approximately 30 millimeters shorter. The rear elements of the 85mm lens for the mount & # 39; E & # 39; of Sony are about 30 mm more embedded in the lens.

The wider diameter of the throat is a factor, as it allows the light striking the edge of the image sensor to hit it at a more perpendicular angle than a narrower throat diameter. This increases the amount of light that falls on each photosite in the same way that every square meter of earth on the surface of the Earth receives more light / energy from the sun when it is higher than when it is low on the horizon. In fact, it would be even more analogous to the amount of sunlight, based on the angle of the sun, that would affect a square of one meter on the surface of the Earth with a solid fence 1-2 meters around, since the pixels Wells in ILC sensors have a depth that generally exceeds their own width.

¹ The support & # 39; A & # 39; of Minolta / Sony had a recording distance of 44.5 mm and a throat diameter of 49.7 mm.

² Previous mounts & # 39; FL & # 39; and Canon's FD had a throat diameter of 48mm that was 4mm wider and sat 4mm closer to the film than the saddle & # 39; F & # 39; from Nikon, which gives them a slight advantage when it comes to designing large aperture lenses. Average focal distance ranges. That's one reason Nikon's 58mm prime could be designed differently than its 50mm cousins. The difference of 3.5 mm between 46.5 mm and 50 mm is not enough to adapt to all the necessary lens elements for superior quality, but with a simple design of 50 mm.