It’s getting more confusing for beginners in photography when viewing the picture below. Photographers call it the exposure triangle, and once you understand the principles of this theory, you will certainly make better photos.
But let’s make it simple…
As a beginner, I suspect that you prefer to use the automatic mode of the camera, which is OK and nothing to be ashamed of, but let’s be honest, you will never shoot the best photos. I recommend you learn as soon as possible the Aperture or Shutter Priority modes, depending on the subject and the result you want to achieve.
In this mode, you control the opening of the lens iris. This means you decide how much light will go into the camera. The camera takes care of the shutter. A wider aperture (or lower f-number) means more light will be let in by the lens, simply because the opening is larger. A narrower aperture (or higher f-number) allows less light to reach the sensor. Aperture Priority gives you better control of the depth of field. This mode is recommended when the subject is not moving fast, resulting in a sharp image of the subject with a blurry background.
Shutter priority allows the photographer to choose a shutter speed setting and allow the camera to decide the correct aperture. Shutter speed is a measure of how long the shutter remains open; in other words, how long the sensor is exposed to light. Faster shutter speeds give the sensor less time to collect light resulting in lower exposure. Slower shutter speeds allow more time for the sensor to collect light and result in higher exposure. If you want sharp images of flying birds, shutter priority is the mode to choose.
This is the mode that I use most often. You decide both Aperture and Shutter Speed. Only use this when you really understand the principles of photography. Depending on the situation, I choose between Aperture, Shutter or Manual mode.
What about ISO?
Since all modern Digital Cameras are getting better in noise handling, I use automatic ISO, so I don’t need to worry about an extra setting! Most cameras allow you to set an operating range, the camera chooses the best ISO number between that range. For my Fujifilm X-T3, I set the range between ISO100 and ISO3200 depending on the light quality.