Re:Why are modern 50mm lenses so damned complicated?
by Zak on Thursday May 13, 2021 @07:40PM
(#27148891)
The intensity of the light is reduced because the aperture is the same diameter (50/3.4 = 25/1.7), but the light has to cover four times the area. To get the same exposure with double the f number and the same shutter speed will require four times the ISO.
> what determines in the same scene how much light is received by the sensor depends on the size of the aperture in milimiters
That's true, but the amount of light is not the intensity of light.
Re:Why are modern 50mm lenses so damned complicated?
by sudosysgen on Friday May 14, 2021 @11:59AM
(#27155669)
It's the amount of light that decides the amount of noise.
Yes, you will need four times the ISO. But you will get exactly the same amount of noise.
As for light angle, it's a consequence of the second law of thermodynamics, that translates in optics as the conservation of étendue.
Basically what this means it that the amount of light captured from a light source is equivalent to the solid angle of light from that light source onto the entrance pupil - whose size is the focal length divided by the f number.
So basically, what determines in the same scene how much light is received by the sensor depends on the size of the aperture in milimiters.
So on a sensor of the same efficiency, it's the physical size of the aperture that determines how much light is captured.