This is page 2 of 4. "Aperture" begins here.
Focal length is the distance from your lens that is in perfect focus.
For example, let’s say you choose an f-stop setting that ultimately gives you--- You know what!? Forget it. This takes algorithmic figuring and we don’t need it here.
Suffice it to say that the depth of field in any given picture will vary according to your f-stop settings. The camera will do the rest.
You will notice that most of my pictures have a specific subject. That means I mostly want to hone in on just the one thing. I prefer the background be blurred out.
Blurring the background is known as having a short depth of field. The other extreme is called a long depth of field. That is when everything in your view finder is in focus; whether it is close to you or far away. Makes sense, huh!?
In this picture I want a long depth of field (High number on my f-stop - like f11 or higher) because I want everything in focus.
It works huh!? It works for me.
Exactly What is aperture?
So, now maybe you’re asking exactly what is aperture. However, what aperture does and how one controls it is more important, but since you asked.
Inside the camera and lens is somewhat like an eye. There is an opening that changes size depending upon the settings you choose. It is called the aperture diaphragm. This is different than the shutter which also opens and closes according to choices you make.
Compare it to your eye. The shutter is like your eyelids. They open and close to allow or not allow light in. Like your eyes, the shutter in a camera is generally all the way open, or all the way closed, with just a split second between the two as the shutter moves.
The aperture is more like your pupil that grows larger or smaller in order to change the amount of light that gets in while the shutter (eyelids) remains open. The aperture diaphragm and the shutter are interdependent.
Kinda like on ol’ married couple. The shutter decides whether or not light comes in. The aperture diaphragm decides how much light actually enters during the time that the shutter allows. To get proper exposure they have to balance.
The number setting for your aperture is inversely proportional to the opening size. I’m using big words to impress you as to how smart I am, but that just means they are opposite. Big number, small opening. Small number, big opening.
Take a look at the first picture below.
The aperture setting in the top picture is f32. (Big number, small opening) The middle picture is about f11. (Medium number, medium opening) The bottom f4.5. (Small number, large opening) Notice the last number has a decimal point. It is not 45 but 4.5.