Aperture Tutorial

 

The Aperture is one of the two settings on your camera that control exposure (Shutter Speed is the other). The Aperture does more than control the exposure level of the photograph, however. It also controls how much of the image is sharply focused!

When you focus, using either autofocus or manual focus, you are actually setting the lens to render objects at a certain distance sharply. Anything the same distance from the camera as the object you focused on will also be sharply focused. Anything further from the camera will be out of focus, as will anything closer to the camera.

The aperture lets you control "Depth of Field." Depth of field refers to the range of distances that will be sharply rendered. Some aperture settings give narrow depth of field. That means that anything not at the same distance that you focused on will be blurry. Other aperture settings will give wider depth of field. That means that things behind and in front of the focused distance will also be sharply focused.

This is a very useful control, because sometimes you will want everything in the photo to be sharp, and other times you will want the background and foreground to be out of focus. We'll look at some examples later on in this tutorial.

 

What Is The Aperture?

The aperture is a mechanical iris inside the lens that opens and closes to control how much light passes through the lens to reach the camera's sensor or film. It works just like the iris in your eye!

 

F-Stops

Lenses use a standard progression of apertures, which are called "F-Stops." When talking about aperture values, photographers will say the letter F then the number that denotes the aperture setting. F11 or F5.6, for example.

The standard F-Stop numbers are:

F1, F1.4, F2, F2.8, F5.6, F8, F11, F16, F22, F32, F45, F64

Your lenses won't have all of those numbers. Few lenses made today have lower numbers than F2.8 or higher ones than F22.

 

What do the numbers mean?

With shutter speeds, the numbers are easy to understand because they're numbers that tell you exactly how long the shutter will stay open. If you're reasonably good at math, you know that ¹⁄₂ of a second will give more exposure than ¹⁄₅₀₀ of a second.

Apertures are, unfortunately, less intuitive. The F-Stop numbers are the opposite of what you would expect. The lower numbers, like F2.8, give wide aperture openings that let in the most light. High numbers, like F16, are the small aperture openings that let in less light.

The standard F-Stop numbers are exactly one stop apart; so going from F-Stop to the next higher one will give one stop less exposure, and going to the next lower F-Stop will give one stop more exposure. Most digital cameras also allow you to set intermediate speeds at ¹⁄₃ stop increments. For example, F3.5 and F4.5 are the intermediate F-stops between F4 and F5.6.

 

Lets look at some examples

In all of the photographs below, I focused on the front of the hood ornament. Each was shot at a different F-Stop, starting with a very wide opening of F1.8 and ending at a very narrow opening of F16.

The first image is a 100% magnification of the hood ornament from one of the photos, so that you can see what the focus point in all of the photos was.

The rest are the full images, so that you can see how the overall image looks at different F-Stop settings. You can click the full-image pictures to see a larger version.

 

 

 

 

 

 

 

 

 

 

 

The images above were made with a 45mm F1.8 lens. That means the largest aperture opening the lens offers is F1.8. As we go down through the example photos starting at F1.8 and going down through the scale to F16, you can see how the photograph changes at the different F-Stops. As mentioned earlier, all of the photographs were made with the lens focused on the front of the hood ornament.

At the widest aperture, F1.8, everything behind the hood ornament is very soft, out of focus. As we move down through the aperture settings, the background begins to change as the area of sharp focus begins to extend into the area behind the hood ornament.

By the time we get to F16, everything on the truck is sharp and even the stuff further in the background, like the building and trees, have become much sharper (though not critically sharp). The hood ornament's appearance, however, has not changed. It will always be sharp because it is what I focused on.

 

 

Examples

 

Portraits are often done using wide apertures to give a soft, out of focus background. This makes the sharp subject stand out from the background, isolating the person from the environment. It also makes distracting objects and shapes in the background less obtrusive. This is my son at age 4. He just graduated from college!

 

 

An environmental portrait portrays the person in his or her working or living space. The environment is important because it tells you something about who the person is. In this case, the background is not a distraction; it is an important part of the image, so you want it to be in focus.

I used a small aperture for this photograph of 84 year old Virgil Hoke, the owner of a small plumbing supply shop. Virgil is very oldschool. He has never used a computer, so billing and recordkeeping is done with old-fashioned paperwork, typed up on an ancient typewriter that he bought new many decades ago.

 

 

Photographs of building interiors often have a lot of depth - things close to the camera and things far away. Usually you want them all in focus, so a small aperture is used.

 

 

Like the interior scene we just looked at, landscape scenes usually have a lot of depth. Most of the time, you want everything in focus; so a small aperture is used.

 

 

This scene is really flat. It does not have a lot of depth; everything is about the same distance from the camera. For a subject like this, its best to use a medium aperture. A small aperture is not needed because there isn't a lot of depth that needs to be kept in focus. I didn't use a large aperture because most lenses are not as sharp at wide apertures as they are in the middle of the aperture range.

 

 

Very Wide Apertures

Many photographers are obsessed with very wide aperture lenses, meaning those with apertures wider than f2. Manufacturers in recent years have turned out a lot of lenses with maximum apertures of f1, f1.2, f1.4. There are even a couple of 50mm lenses with maximum apertures of f.095!

It is often said that such wide apertures are "Needed" for low-light work, or for portraits (for out of focus backgrounds). I would suggest that most of the time, such lenses are not very useful for real-world photography and are not worth the very high prices they sell for and the inconvenience of carrying lenses that are very large and heavy compared to lenses with more modest maximum apertures like f2 or f2.8.

 

 

Portrait of my grandfather, Charles Crawford. Made with a 50mm lens at f5.6 to ensure that his whole face is sharp, but the background is still soft.

 

The problem with very wide apertures is that there is virtually NO depth of field. If you're doing a portrait with an f1.4 or f1.2 lens used at the widest aperture, the zone of sharpness will only be a few millimeters in front of and behind the point you focused on.

For portraits, you should focus on the person's eyes (if the subject is not looking directly at the camera, focus on the closest eye). Using a very wide aperture setting means that the eye will be in focus, but the tips of the eyelashes may be out of focus! The rest of the face, like the nose, mouth, and ears, certainly will be. In actual practice, best results come from using a moderately wide aperture like f4 or f5.6 for portrait work. This gives enough depth of field to keep the whole face sharp, but still allows the background to fall out of focus.

 

 

Are Very Wide Apertures Ever Useful?

As the example below shows, there are situations where very shallow depth of field can be usd as a creative element. Even then, I used f2 for that image rather than the very wide apertures many lenses offer today. At f1.2, the depth of field would have been so shallow that the entire clothespin would not have been sharp. Of course, you might prefer it that way, so you have to make your own decision about whether a very wide aperture lens is worth the cost and inconvenience (remember that those lenses are very large and heavy).

 

Clothesline at an abandoned farmhouse. I shot this at f2 to throw everything out of focus except the old wooden clothespin in the front.