So you have bought yourself a nifty DSLR camera and are ready to start capturing some amazing pictures, perhaps you have been to a couple of photography classes, or learned what you need to know to get started with your new awesome camera, and as excited as you are about your camera, you probably take the time to just admire it.
But have you ever wondered what that random button is for on the face of your camera body, close to the lens detachment button, is used for?
What you are looking at is what you call the depth of field preview button, and strangely, not many people know its true purpose.
When you are looking through your viewfinder, you are always looking through it at the lenses maximum or widest aperture regardless of what aperture setting you are set to, until you actually take your image. This is designed so that you can physically see through the viewfinder with sufficient light.
So if you are planning a shot with a small aperture such as F16 - F22 and look through the viewfinder, you'll always get a shallow depth of field preview. So if you want to get a true indication of what your depth of field will be like before taking the image, hold down the depth of field preview button while looking through the viewfinder before taking the shot.
Take a look at the video below by the YouTube channel:
ZY Productions on the Depth Of Field Preview Button Explained...