Throughout photography there are relationships that can shape the quality of any given photograph. A number of my students come into my class claiming that they have a “good eye” and they just want to learn enough technique to make sure that their exposures are good. I also have students with a good deal of technical ability and thought that was the beginning and end of what photography should be about. I see it as my job to teach them that there are relationships between the technical side of photography and the aesthetics of photography. It is my contention that the best photographers are those who have a good technical background along with an understanding of the aesthetical issues available in any given photographic situation and apply them to best advantage.
The first thing to realize is that photography is full of relationships, both technical and aesthetic. Photographers learn early on that in order to get a correct exposure it is a relationship between the metering system, the ISO setting and the exposure system. It is a combination of those three camera functions that allow for the camera to give you a correct exposure, at least the majority of the time. The metering
tells the exposure system how much light is coming through the lens, the ISO is telling the exposure system effectively how sensitive the sensor is to light and the exposure system then is able to select an f-stop/shutter speed that will allow the correct amount of light to the sensor so a photograph can be made. (I know this is very basic stuff, but hang in there with me for a little bit). Having a correct exposure is usually enough for the beginning student of photography. After all, how many bought a fancy expensive camera and still cannot get a good exposure? But there is more to it. Because you are not tied into that one f-stop/shutter speed combination that the camera came up with, if you know the relationship between f-stops and shutter speeds. This relationship can give you any number of correct or equivalent exposures limited only to the number of f-stops and shutter speeds available and if the initial exposure were correct then they all would be. Still, pretty basic stuff.
But here is where another relationship comes in; both the f-stop and shutter speed will affect the look of the photograph as it pertains to motion (the shutter speed) and the way depth of field is depicted (the f-stop). This keeping in mind that the f-stop is only one of three factors that affect depth of field. Each has their own influence on what the depth of field becomes and should be considered as a total effect when trying to predict what the depth of field might be. Which of the equivalent exposures you select will be important to the final outcome of the picture in an aesthetic sense.