Among the three aspects that are most important in mastering a DSLR lies aperture and how to use it. In my opinion, it is the most difficult to fully grasp. Exactly what it does in your camera and what it means for your photo is a knowledge base that propel your images towards your visions. The good news is, there isn’t much to it.
As I wrote before, aperture is like the pupil of an eye. There are a series of blades in your camera that converge together or spread apart. The wider apart they spread, the bigger the hole in the middle is. The bigger the hole in the middle is, more light gets into the camera, and vice versa. This will impact the ISO and shutter speed settings.
Aperture is measured in f-numbers which I (and some others) call f-stops or stops. The number is a calculation using the diameter of the hole in the middle of the blades and how far away something needs to be to focus on it. It will typically show up on your lens (which is the lowest f-stop it’s capable of). For example, my favorite lense is a 85mm Nikkor f/1.8G which means at f1.8, my lens is wide open. For all intents and purposes, you just need to know that the lower the f-stop, the wider the hole. If the f-stop is higher, then the hole is more narrow.
Here is where the magical knowledge of aperture comes in. It is what makes backgrounds ‘blurry’. That blur in the photography world is called bokeh. If the f-stop number is low, then the background will be blurrier. Or, if the hole in the middle of the blades is wider (more open), then the background will be blurrier. Now, this is a blanket statement and it does depend on more variables. It is a good rule to start with, however.
So we can assume that the higher the number gets the more in focus the background and everything will be in the picture. This tradeoff is something you need to make an artistic decision on. The wider the aperture, the smaller span of focus. For instance if my lens is wide open, then I may have everything from 5 feet to 5 ½ feet in front of me in focus. If it is closed, then I may have everything from the minimum focal distance to infinity (and beyond!) in focus.
Different lenses have different optics and images will look differently with each. One reason for this is they have different blades. Typically there will be 5, 7, or 9 blades. It is purely a matter of opinion as to which is best. This is going to make up what the bokeh looks like. More blades forms a more round circle which translates in the blurred parts of the background being more smooth. Most lenses will have 7 blades, and more blades is typically more expensive. Simply Google search “tech specs of (insert your lens or camera name)” and it will usually give you a chart or list which will plainly tell you how many “diaphragm blades” are in it.
Aperture is a dense topic that impacts your picture greatly. It is important to at least have a basic understanding of it in order to understand why your picture looks the way it looks. Use the aperture priority shooting mode on your camera and play with it until you ‘totally get it’. Then, you can start leveraging that knowledge against ISO and shutter speed to see what kind of images you come up with. Follow me on twitter for more photography tips and tricks!