An
f/0.8 aperture is an extreme feat of optical engineering. To understand how it works, you have to look at it as a ratio of light-gathering "hunger" versus the physical size of the lens.
In photography, the "f-number" is a mathematical fraction:
f-number=diameter of entrance pupilfocal length
For a lens to be f/0.8, the opening that lets light in (the entrance pupil) must actually be
larger than the focal length of the lens itself. If you have a 50mm lens at f/0.8, the "hole" letting light in is a massive 62.5mm wide.
1. The Physics: How it Gathers Light
An f/0.8 aperture works by bending light at extremely steep angles to cram as many photons as possible onto the sensor.
- The Light Torrent: Compared to a "pro" f/2.8 lens, an f/0.8 lens lets in about 12 times more light. This allows you to shoot in near-total darkness without needing a flash.
- The f/0.5 Limit: In physics, the theoretical limit for a lens in air is f/0.5. As you get closer to this number, the light rays have to bend so sharply that they eventually reflect off the glass instead of going through it. An f/0.8lens is operating right at the edge of what’s physically possible.
2. The Result: "Paper-Thin" Focus
The most dramatic effect of f/0.8 is the
Depth of Field (DOF). Because the light is coming from such a wide "eye," the plane of sharp focus is incredibly narrow.
- The Eyelash Problem: If you take a portrait at f/0.8, you might have the subject's iris in focus while their eyelashes and ears are already a blurry mess.
- Bokeh: The background blur is creamy and "painterly" because the out-of-focus light points (circles of confusion) are physically huge.