The world of photography has moved so much since the dawn of digital. The flexibility, in camera adjustments and the ability to see the image taken, immediately – are immense.
The Aperture Shutter Relationship
Aperture and shutter relationship are (1) both optical and (2) interdependent. They both control the amount of light that gets to the cameras sensor. There is a ideal setting where the light hitting the sensor is at its optimum, let’s call it 1-to-1. then if you increase one of the settings to 2, you have to compensate by decreasing the other setting by half so we get 2-to-1/2.
Changing the combination controls depth of field (see this article) or shutter speed (see this article)
In a dark, low light environment, we change both the aperture and shutter speed to allow more light in so that the image is usable. But there are limits to this and compromises to be made. Increasing the shutter speed to much introduces camera shake. Whereas increasing aperture reduces depth of field. But in the digit photography world we have a third control, described next.
Digital photography also brought a new control to us, the ISO setting. Originally, in the old film world, the ISO (also referred to as the ASA number) represented the speed of the film. You put the film in the camera and set it’s ASA number to the value on the film canister. But not anymore.
The ISO number has become a third control, that you can alter between shots. It acts like the gain control in an amplifier. The best way to describe this control is like the volume control on an AM radio.
Obviously the volume control makes the sound (or noise if my teenagers have tuned the radio) louder or softer. But sometimes, when the AM signal is weak, you have to increase the volume much more for normally listening and that introduces NOISE.
Noise works the same way when you dial in a higher ISO number on your camera (because of low light). The light source is low and so you compensate by increasing the cameras sensitivity but as you do this the image quality suffers and will look more and more grainy as the ISO goes up.
Software to the rescue
This is the only control on the camera where optics aren’t used, it’s purely electronic and because of this computer algorithms are used to compensate for the high gain (high ISO) in the image. As the years have gone by so the algorithms have evolved and the images are getting better and better in low light and at night.