Helen B
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Same size hole equals...same aperture value?
F-stop is a ratio of the focal length relative to the lens aperture.
Consider an 18-55 mm f/3.5-5.6 kit lens.
At 18 mm and f/3.5 the diameter of the lens aperture is - 18/3.5 = 5.14 mm wide
At 55 mm and f/5.6 the diameter of the lens aperture is - 55/5.6 = 9.82 mm wide.
With the lens set to f/3.5 at 18 mm, the f-stop is not changed, and the lens is zoomed from 18 mm to 55 mm, the lens aperture actually gets larger.
This can be confusing, possibly because of the lack of distinction between the physical lens opening and the entrance pupil. The f-number (which is a defined term) is calculated from the diameter of the entrance pupil, not the diameter of the physical opening. The entrance pupil is the image of the physical opening as seen from the front of the lens. Because it is an image, its magnification can change as the front lens elements move during zooming, thus the size of the entrance pupil can change even though the physical aperture remains the same. This effect happens with both variable aperture and constant aperture zooms. It may be combined with some change in the physical aperture.
The Angenieux adapters were for video/film zoom lenses - ie things that cost tens of thousands of dollars. Even though I had a few Angenieux zooms I decided they weren't for me, and I don't think they were widely used.
The Metabones website does mention other lens mounts and other camera mounts. The m4/3 version has different optics from the E-mount version. Brian Caldwell has optimized the optics for the different formats.