What is aperture on my camera?

And why should I even care about aperture anyway?

There are three interdependent variables in digital photography.

Shutter Speed

Aperture (f-stop)

Film Speed

Throughout the pages of this site I talk about how these three interrelate. For now just remember each will affect the other two. When you understand and find the correct balance your snapshots will transform into photographs.

The f-stop decides what is in focus and what is not. That is why you should care. Unless you don’t care what your pictures look like.

If that is the case, then quite frankly, maybe you’re on the wrong website. There’s a multitude of more entertaining sites than this if you have no interest in the end result of your photos.

On the other hand if you are here seeking simple steps to achieve professional looking photographs, you are in the right place. f-stop variations will go a long way toward that end.

Take a look at these two pictures. Which is more professional looking?

Other than the position of the bird, know what the difference is? The f-stop. Yep, that’s it! The only difference. They were each taken within seconds of the other. Both were taken on a tripod using the same camera and lens.

Notice how rich the top one looks. Notice how the top picture has real and noticeable depth and dimension. Pay close attention to the water pipe. That has not varied between the pictures. Yet in the first picture it has life. In the second picture it is flat and lifeless.

The difference is very noticeable at this tiny size. Imagine the difference at 8”X10” or larger.

The things in your picture that are in focus…

as opposed to those that are not, is known as depth of field. That is the distance from your lens that things come into focus and the distance they once again go out. Depth of field varies in length and position.

It can start several feet from your lens and end shortly thereafter. It can start, let’s say, at 50 feet and end at 70 feet. Or it can start right out of the lens and go on to infinity. It all depends upon the f-stop you choose and your focal length.

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 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. What it 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.

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.

Each lens has its own numbers and size correlation. But universally the “f-stop” number and the opening size are inversely proportional.

The largest number correlates with the smallest opening and provides the longest depth of field. The entire picture should be in focus.

Your DSLR camera has a button you can press to see what will be in focus when you shoot. As you push the button the viewfinder grows dim and everything comes into focus. With a Point & Shoot you monitor the screen.

This again can be compared to your eyes. You know how you have to squint then everything kinda dims but comes into focus? Same thing. The ol’ eyes just ain’t what they used to be are they?

A good way to remember is; the larger the number, the more of your picture will be in focus.

The larger the number, the longer it takes light to travel through the lens while the shutter is open. The shutter will have to remain open just that much longer in order to get the right exposure for the shot.

Here is how all this adds up.

We have been talking about the largest number. I use the smallest number whenever possible. That’s the largest opening. It does a couple of things.

Being inversely proportional, the smallest number has the largest opening and allows the most light through the lens in the shortest amount of time.

Hence, first you get the fastest shutter speed. If you have read my "Best Camera Settings" page you already know I want a fast shutter speed to avoid motion blur.

The smallest number gives you the shortest depth of field. That is the shortest distance within your picture that is in focus. It gives the shot a more professional look and feel by seemingly concentrating on your subject.

So, the second thing a small number does, having this short depth of field, is blurs out the background while my subject remains in clear focus. This helps my subject stand out. It is in focus while everything in front of and behind my subject is blurred.

Thirdly it helps obscure any dirt and smudges that happen to be on and between the outer most lens and the image sensor inside.

Check it out. The first shot is at f2.8, the second at f34.

Quite a difference in the amount of dirt that shows, huh!? Understand, this is super enlarged to make my point but there is always some dirt inside a camera. Even from the factory. When you use a very large number dirt and smudges are likely to show in your finish photo.

There are plenty of times to use the large numbers. For example in the church above I wanted both the foreground and the church to be in focus. So I used an aperture of f14. That was high enough to keep everything in my lens focused.

You can test to see how clean your camera is by setting your f-stop as high as it will go, set your ISO to 100 and using a tripod, shoot a picture of a blue sky. For best results make sure you manually focus your camera to infinity.

Once you have the shot, put it in your computer and just open it up. You will see any dirt that happens to be anywhere in the light path between the outer most lens and the image sensor surface.

Now figure out where it is, by elimination, and clean it up. There are places in the camera you won't be able to reach. In that case, if you want it cleaned up, you'll have to take your camera to a repair shop.

Let’s compare when we're taking a picture.

The next two pictures were taken in “Aperture Priority.” First I used f3.5, second f22. Most times I want my subject crisp and the rest of the frame blurred, like the top picture.

This picture, however, I feel should be in focus throughout. In the foreground is the canon. Midway to the mountains are the flags and then in the background are the mountains which I want showing clearly.

I feel the photograph is more effective being in focus throughout. The next one however, I feel is a personal choice. I can see either being preferred.

In the top picture, f5.6 the subject is the background. It is the boats. So blurring out the window frame in the foreground can work.

In the bottom picture, f34 there are two main subjects. The boats in the background and the window frame with the beveled glass, in the foreground are both notable subjects.

For me personally, the bottom picture works better. But it is the choice of who ever is viewing the photograph.

For general, hand held shooting go here.

One final thought. In the next series of pictures I set the camera for the correct exposure in the first picture. In the second picture all I did was change the aperture to a very high number. I left the shutter speed the same.

The purpose of this comparison is to show how the shutter speed must change when the aperture changes or the picture will be exposed wrong. The top picture was taken at f5.6 and a shutter speed of 1/400th of a second.

This shot was at f34, still 1/400th of a second shutter speed. As you can see one would have to keep the shutter open much longer in order to get the same approximate exposure as in the first picture.

Finally this picture was set in the middle at f8. The shutter speed was still 1/400th of a second.

There you have it. Aperture, what it is and why we need it when we want professional photographs. Now go out and practice until it becomes second nature.

This whole page boils down to...

Large number, much in focus. Small number, little in focus. So the aperture rule of thumb is, use a large number when you are shooting (large) landscapes and a small number when you are shooting (small) people or animals.

For tripod mounted guidelines go here.

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