Whether you shoot on a cheap cellphone or a high end DSLR, whether film or digital, every camera essentially relies on 3 variables: aperture size, shutter speed, and ISO.
Aperture size
An aperture is a window that lets light in - the bigger the window, the more light enters the camera and the brighter your photo will be.
Conversely, the smaller the aperture, the less light enters the camera and the darker your photo will be. You can adjust the aperture, or the other 2 variables, to ensure that your photo isn't too bright or too dark.
The aperture is typically controlled (i) manually by an aperture ring on the lens; (ii) manually using a dial on the body of the camera; or (iii) automatically (like in camera phones or if you are shooting using an automated mode on your camera)
Aperture size is represented by an f-stop number. Usually you'll see your current aperture setting somewhere on your camera, whether it's on the aperture ring, camera screen, or through the viewfinder:
f22
f16
f11
f8
f5.6
f4
f2.8
f2
f1.8
f1.4
These are called "f-stop" numbers. Rather counter-intuitively, the larger the aperture size, the smaller the number, and vice versa.
Almost all lenses, and cameras with built-in lenses (excluding cellphone cameras), indicate the largest aperture size that the lens is capable of. It's usually somewhere on the front, and expressed in the form "1:X" where X is the maximum aperture size.
In the example below, the lens is an 85mm lens, and the maximum aperture size is 1.8. You can also see from the photo that the aperture is opened up - it's in fact as big as it can go, because I have set the aperture to f1.8.
Aperture size also impacts something known as depth-of-field ("DOF"). DOF refers to a range of distances within which things appear in sharp focus.
A large DOF means that objects in a wide range of distances will be in focus. A small aperture (large aperture number) gives you a large DOF.
Shot at f8 - everything is in focus
Conversely, a shallow DOF means that just a sliver of things will be in focus, and everything else will be blurry (called "bokeh"). A large aperture (small aperture number) gives you shallow DOF. You'll often find bokeh in portraits, where it's used to blur out distracting backgrounds and focus the viewer's attention on the subject.
Shot at f2 - only the head is in focus
To summarize, here's a table of how aperture affects your photo-taking:
Please consider sharing your photos with the community by tagging #dharmaportraits on your Instagram photos - I'd love to see how you're using these tips to create beautiful photos.