In my opinion, the global shutter of a full-frame sensor is a great innovation for consumer digital cameras. I would like to see the next big step towards low ISO support.
Digital cameras already emulate low ISO with hidden positive exposure compensation, but it is rather useless because of possible highlight blowouts.
My reasons for using low ISO:
1. With very fast lenses.
2. For motion blur.
3. To increase the signal-to-noise ratio.
What are possible solutions?
Sony a9 III shortest shutter speed is 1/80000. According to the Sunny 16 rule, this is enough for f/1.0 and slightly faster lenses even at native ISO250 ( (1/250 * 1/((16/1)^2) = 1/64000, calculated shutter speed for ISO250 and f/1.0). Practically, I think 1/80000 is enough even at f/0.7.
For two other purposes, I would like to see low ISO emulation through image averaging. In this mode, the photographer chooses the emulated shutter speed. This speed is the sum of several cycles with a shorter shutter speed (of the global shutter). The number of cycles depends on the native ISO and the emulated ISO ratio. For example, ISO25 is emulated by 10 cycles at ISO250, so the shortest emulated shutter speed is 1/80000 * 1/10 = 1/8000.
The captured images are averaged to produce the final image. This increases the signal-to-noise ratio and can create the desired motion blur effect. When shooting in raw, the number of bits per sample can also be increased.
Obviously, the delay between cycles should be as short as possible in order to use this emulation without intermediate image alignment and transformation. And also as stable as possible to get an adequate motion blur effect.
See also related notes:
- Sony a9 III: Full-frame with global shutter (2023-11-13)
- Камера Nokia 5.3 и уменьшение шумов слабых матриц (2022-05-09)
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