Let's talk about manually exposing our aperture as part of the exposure triangle. We know that there are three elements to exposing a photograph. ISO, aperture and shutter speed. Aperture is the opening of the lens. Its the hole. The smaller the number, the bigger the hole in the lens, the more light comes in from nearby. When we tighten that aperture, when we close it up with a bigger number; the hole being smaller, is drawing light in from further away, and we're missing out on some of this ambient light. The bigger the hole, the blurrier the background; is probably the easiest way to explain it.
And that's where you get those beautiful bouquets or the beautiful blurry backgrounds in our photographs and in our portraits.
When we make that hole nice and tight, and when we close it to bring that light in further away, we start getting this beautiful element of being able to actually see everything in our background. So its always going to depend really on, on what you want.
Do you want the background in your shot or don't you want the background in your shot? What's more important, a tighter focus or a wider focus in your photograph? By using our aperture, in conjunction with our ISO and our shutter speed we can effectively manually expose our photograph