The properties of each setting are as follows:
1. ISO — this is the equivalent to when we used film for cameras thus, this is representational of the film speed, or in other words, the film sensitivity. The higher the ISO value (ex 6400) the less light that was necessary to produce an image whereas if you were shooting outdoors on a sunny day, you could get by with an iso of 400 as there is abundant light available. Each of these ISO settings has specific characteristics for example, when shooting film (and even digital) a higher ISO (used for low light situations) will result in more “grainy” images where if not metered and exposed correctly can also lead to a “muddy” look as the image will be lacking in contrast and clarity.
SHUTTER SPEED — this is the speed at which the shutter or some prefer to envision it as a “curtain” opens and shuts in order to control the length of time that the film or sensor is exposed to the light. You might think of it like this... while the ISO is representational is the the ambient light situation the SS is how much of that ambient light you are able to record when the shutter is released. Shutter speed is also used to stop motion or to provide a sense of moving within an image. A higher shutter speed will stop motion and Depending on how fast the subject is moving will dictate how quickly your shutter is open to record the light and image for example, to stop a running child should be at least 1/200 but most likely until the photographer is well versed in the art and their camera it might be best to stay on the safe side at 1/500. To show motion, like a moving train, you’ll want to stop down to a slower speed to enhance the “blur” of the movement which allows the image/artist to tell more of a story. To be sure that your hand shake does not cause an out of focus image due to the inevitable vibration that can affect the shooter based on the weight of the camera and glass/lens... a good rule of thumb is to double the lens size to avoid any dreaded effects while hand holding. So for example, for crisp images do not shoot below 1/125 when shooting with a 50mm until you are experienced and then you’ll learn how far you can push that rule.
APERTURE — this is the setting that will affect the opening in the lens at which the light will come thru. The aperture can affect the depth of field and can also allow more wiggle room for low light shooting as you can “open up” to aperture as wide as 1.4 (Nikon) or even 1.2 (canon). It’s tricky as the lower the the aperture setting (the actual value; 1.2, 1.4, 1.8, and so on all the way up to 22), the more the lens opens... which increases the amount of light that is let in as well as creates a much shorter depth of field (how the artist obtains the less In-focus / blurred background called bokeh). Whereas the higher aperture number (but smaller opening) lets in less light and extends the depth of field to allow more of the image to be on the same focal plane which then allows for more of the environment/subject to be in clear and sharp focus. This can be an artistic choice but traditionally you’ll see portraits shot more wide open vs landscapes or street photography which will have more details on focus and shot with the lens closed down more.
