E-mount for Nikon MILC, good idea or not?

Started Sep 23, 2017 | Polls thread
bobn2 Forum Pro • Posts: 58,130
Re: E-mount for Nikon MILC, good idea or not?

cosmicnode wrote:

bobn2 wrote:

cosmicnode wrote:

bobn2 wrote:

Antonio G wrote:

One of the problems a lot of people points out against the use of the F-mount in future mirrorless models is the lens throat diameter that prevents designing/using the ultra-fast aperture lenses and the E-mount wouldn't bring any advantage there as it shows just 2mm more and still far from other competitors.

It's not just the diameter of the mount, it's the register. The E-mount has a register of 18mm whilst the F mount is 46.5mm. It means that the E-mount straddles the exit cone from the lens where it is much narrower, therefore the mount can be narrower. That being said, the F-mount can go down to f/1.2, and there haven't been many faster lenses at FF.

You have this back to front

I really don't.

the actual distance from the rear of a Sony lens to the sensor is approx 12mm taking into account the thickness the lens protrudes into the mount. this makes it harder to cover the sensor than the similar F mount with a 47mm registration distance where you can have a larger cone . Think of it like this, the largest opening in the lens barrel can be about 39mm, move this even closer to the sensor until it is touching and you eliminate the sensor corners completely from the exit cone.

That's a different effect. What we are talking about is what can be the subtended angle of that light cone. Yes, you're right, in that in that extreme, the mount would shade the edges of the frame. However, as a sanity check, think of the Classic Canon 7, which used the 39mm Leica screw mount (register 28.76mm) and came with an f/0.95 lens.

This lens didn't actually mount on the screw mount, but the clear aperture was 39mm.

Consider long telephoto lenses, they are in the position with the short registration distance of vignetting caused by the rear element being a good distance up the lens barrel, my 200-400 has the rear element some 80-100mm away from the sensor

Do your 200-400 or 80-100 have an f-number of faster than f/1.4? That's what we were talking about. In any case, pretty much every designed for digital lens has the exit pupil something like 100mm away from the sensor, even if they are wide angles. Just do the geometry, even in the far corners, hardly any of the exit pupil is shaded by the lens mount aperture, probably not enough for the vignetting to be noticed. Here's a diagram to show you what's happening

On the right is the exit pupil of an f/1 lens, 100mm from the image plane (actually the distance doesn't matter, because the light cone always subtends the same angle, in proportion to the f-number). On the right in cyan is the 43mm image diagonal. In green is the 40mm aperture of the lens mount at 18mm register. As you can see the dark green shaded area is the part of the exit pupil obscured, in the end maybe 1/3 of the exit pupil (can't be bothered to do the exact sum), 0.6 stop loss in the extreme corners. And of course, that is using a lens not designed for the mount, if the lens is designed with a positive rear element filling the mount circle, there need be no shading at all.

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