Photography 101 — Aperture

Aperture illustration copyright 2016 Thomas Kachadurian

In photography the word aperture refers to the opening of the lens iris. It seems like a simple concept, and on older interchangeable lens cameras it’s pretty easy to see the lens iris (or diaphragm) in action. As the iris opening gets smaller less light is transmitted to the film or sensor. If you increase the size of the iris opening you get more light passing through the lens. That’s the easy part. When you get beyond the basics of exposure, aperture is the most subtle adjustment photographers will make. One of the major distinctions between beginning and advance photographers is their knowledge and use of aperture to control how their photographs render a scene.

Courtney by photographer Thomas Kachadurian

It’s doesn’t take an exotic lens to control depth of field. A 200mm lens at f4 provided shallow enough DOF to separate Courtney from the path behind her and at the same time rendered her in full detail.

The aperture controls the depth of field (DOF) of any lens. A lens can only focus on a single plane, but DOF extends the perception of focus in front of and behind the plane of focus. Roughly speaking that perception of focus is distributed 1/3 in front of the plane of focus and 2/3 behind the plane of focus. A lower f-stop number (larger opening) will have shallow DOF and create separation between the subject and both the foreground and background. A higher f-stop number (smaller opening) will have deeper focus and the photograph will show more of the foreground to background in focus. This is a good starter simplification, but there are subtleties to using depth of field that take years to master.

Depth of field is not an absolute. A short focal length lens will have more DOF than a longer lens at the same aperture number. Very long lenses in the 400mm and above range will have fairly shallow DOF even at smaller openings. Very short lenses, less than 10mm have deep focus even wide open.

Depth of field does not change based on the size of the camera’s sensor, but will change based on subject to camera distance. When the camera is very close to a subject DOF will be shorter. As the main point of focus moves away from the camera we will perceive greater DOF.

The next four images are shot on a camera with a sensor the size of traditional 35mm film, often called a full-frame or FX sensor. On this camera the 28mm lens a moderate wide angle. In the first two images the camera is about three feet from the words “NO TRESPASSING.” In the second two images the camera is at near minimum focus distance.

Essential Aperture Skills by Thomas Kachadurian

From this first image it is clear that even a wide-angle lens can have shallow DOF when fully open. At f2.0 not even the entire fence is rendered in focus, and the buildings in the distance show significant blur.

Essential Aperture Skills by Thomas Kachadurian

At f11 the image has enough DOF that the entire fence is in focus and the distant building, while not in focus, shows defining details. Note that at f11 the window mullions on the distant building are clearly visible, while at f2.0 the mullions can barely be discerned.

Depth of field gets even shallower when the camera is moved closer to the subject. The red words are less than 18” away in the next two photographs. Even with a small aperture the entire scene is not in focus.

Essential Aperture Skills by Thomas Kachadurian

At f11 the whole green column is sharp, but the fence gets soft as it goes into the distance. The far buildings are out of focus.

Essential Aperture Skills by Thomas Kachadurian

With the camera very close to the subject and a large aperture, the focus is very shallow. At f2.0 all the letters are no longer sharp. Even though the critical focus point is the letter I, the R, just a few inches away, is soft.

This Columbine was shot at f3.2 with a 40mm lens. The shallow DOF is primarily a function of the short camera to subject distance.

This Columbine was shot at f3.2 with a 40mm lens. The shallow DOF is primarily a function of the short camera to subject distance.

Depth of field is a curve. There is no right amount of depth of field. Shallow focus is not always the best choice nor is deep focus. DOF is the tool of the photographer. By understanding the three factors influencing DOF, aperture, lens focal length, and camera to subject distance, a photographer can get the correct balance to create the photograph he or she desires. It has become common Internet folly that portraits must have very shallow DOF and the landscape images should have nearly everything in focus. Nothing could be further from the truth. For more than 50 years Playboy has published countless beauty portraits with no shortage of depth of field. The single bloom in shallow focus is and will remain a nature classic.

The next two exposures are made with a 50mm lens on an FX camera at about 25 feet. It is a scene rendered very nearly as our eyes would see it. The lens is focused on the gate.

Essential Aperture Skills by Thomas Kachadurian

Although the lens is set at f2.0, the near wall behind the gate reads clearly as brick, and while we can’t discern the wood grain we can see the windows are covered with plywood. We can see the leaves of the grass in the foreground, but they are not sharp. This is a photograph of the gate that still tells us something about the full setting.

Essential Aperture Skills by Thomas Kachadurian

By stopping down to f8 the focus is extended to the near wall behind the gate and in front of the gate to the clumps of grass in the foreground. The far walls nearly appear in focus. But does the photograph benefit from this added depth of focus?

The added depth of field of the second image brings the foreground grass into focus, which shows it to be unruly weeds rather than a green frame at the base of the image. Given the number of textures, grids and patterns in this image the additional DOF puts the gate in competition with the background without telling us more about the scene. For this landscape photo I prefer the first exposure at f2.

 

Get Closer for Shallower Depth of Field

Subject to camera distance is an often-overlooked factor in determining Depth of Field. Moving the camera will change more than the perspective of a photograph even with the same lens and the same aperture. When the primary subject is 30 feet or more from the camera even a lens with a near normal angle of view will have fairly deep focus at  5.6 or larger f-numbers. Only the near foreground will appear completely out of focus. When the camera is very close to the subject DOF will be very shallow to a point where distant background elements will not appear in focus even at f22.

In the following three photos the chain is photographed at 4 feet a with a 50mm lens on an FX camera. The camera is focused at “2002” on the lock and the camera is tipped down so the plane of focus is not parallel with the chain.

Essential Aperture Skills by Thomas Kachadurian

This photograph is made at f1.2, the largest lens opening available on anything but a specialty lens. At this setting DOF is thin. The lock is in focus but the chain links at the top of the frame are soft. The background reads as green blobs.

Essential Aperture Skills by Thomas Kachadurian

At f4 the full chain and all of the gate are in focus. The background is still soft with good separation from the gate. The background wall, although out of focus, is showing detail that reads as brick.

Essential Aperture Skills by Thomas Kachadurian

At f16 there is slight near-far separation at the top of the frame, but at the bottom the gate and weeds behind it are equally sharp and start to merge. The back wall is not critically sharp, but the details are readable and the metal grate on the window is clearly visible for the first time. There is a great deal of information in this photograph.

In the next five photos I moved the cameras to about 20 inches from the chain. Using the same 50mm lens on an FX camera the lens is focused at “2002” on the lock. The camera is even more tipped down so the plane of focus is not parallel with the chain. If the camera was plumb and in the same plane as the chain the focus planes would follow each other. Because the camera is tipped the plane of focus and the plane of the chain intersect at only the point of critical focus.

Essential Aperture Skills by Thomas Kachadurian

At f1.2, and at close range, DOF is razor thin. The writing “2002” on the lock is in focus but the near chain links at the shackle are already going soft. The chain at the top of the frame is blurry. The background, particularly in the middle of the frame reads as solid green.

Essential Aperture Skills by Thomas Kachadurian

Even at F2 the near links at the shackle are still soft and the background has only clouds of color.

Essential Aperture Skills by Thomas Kachadurian

At f4 all of the chain at the lock appears sharp. The chain at the top of the frame is not yet sharp, but has lost it’s severe out-of-focus look. There is still good near-far separation. The background green reads as foliage but without any detail at all.

Essential Aperture Skills by Thomas Kachadurian

At f8 most all of the chain appears to be in focus. There is still good near-far separation, but the foliage is starting to read as weed. I don’t like the little bright out of focus dots in the green field.

Essential Aperture Skills by Thomas Kachadurian

Compared to the f8 image, this image at f16 is an improvement. There is still enough near-far separation to allow the gate and chain to come out of the background, even at the bottom of the frame. At the same time, because the background is closer to being in focus the light dots in the background foliage read as what they are, clover blossoms.

There isn’t one clearly better photograph. We need to closely consider the details in an image and how aperture subtly effects them. The choices come down to the photographer’s vision. Of the previous five photos the exposure at f4 is my favorite. To my eyes the f8 shot is the worst of the five. The light patches in the background foliage are just getting clear enough at f8 to be distracting but not clear enough to identify–they could be litter or flowers. Interestingly f8, my least favorite of all the choices, is probably what the Auto mode would have chosen for an image on this bright day. The f16 image is an improvement over the f8 image because the background confusion is resolved.

 

It’s Okay to Be Shallow

In a more traditional landscape with both near and far detail it is often considered ideal to have deep focus, but that is not always the case, and may not be the choice of the photographer. The following photographs are made with a 28mm lens, a moderate wide angle of view, on a camera with an FX sensor. The camera is level and plumb at about five feet from the two orange blossoms that are together in center, where the lens is focused. Each of these images has its own merits. It’s not a question of right or wrong, or even better or worse, but a question of which image the photographer wants.

Essential Aperture Skills by Thomas Kachadurian

At f2 the wide lens offers enough DOF that the central blooms are all in focus. The sunflowers in the background and the far building are out of focus. The near foreground foliage in the bottom right corner is out of focus. I personally dislike bright out of focus foreground areas, and if I were to choose this aperture I would burn down the highlights in the bottom right corner before making a final print. This image is about the near garden only.

Essential Aperture Skills by Thomas Kachadurian

At f4 the near foliage and all of the blooms are in focus. The sunflowers are soft, but not completely out of focus. The distant building is out of focus. This image still emphasizes the front blossoms but resolves the blurry foreground and connects the front blossoms more to the row of sunflowers.

Essential Aperture Skills by Thomas Kachadurian

At f8 focus is sharp all the way to the row of sunflowers. There is some softness on the distant building (although it is a bit hard to see on this web resolution image). The sunflowers still have some edge separation from the softer building in the background. This is a photo of the gardens in the context of the area.

Essential Aperture Skills by Thomas Kachadurian

At f16 everything appears in focus, near to far. In many images full front to back focus can be boring and near elements will merge into background elements. In this image light and shadow create enough separation between the elements that full deep focus still works. This photograph is much more about the whole site, the building and the gardens together.

 

More Than One Right Answer

The next photographs are made with a 50mm lens, a nearly naked eye angle of view, on a camera with an FX sensor. The camera is level and plumb with the lens focused on the sculpture inset in the door. The different apertures yield four different images; to my eyes the shallowest and deepest focus are the two most successful. There is only one choice I would reject outright.

Essential Aperture Skills by Thomas Kachadurian

The shallow DOF at f1.4 makes this an image of the sculpture detail in the door with the hint of the garden that lies behind. The foliage frame on the right edge is soft, but because it has no significant highlights it isn’t distracting. The limited focus makes this an inviting and moody image.

Essential Aperture Skills by Thomas Kachadurian

The image is similarly moody at f2.8, but not as successfully. More of the door is in focus. The additional detail in the door is not unwelcome, but it does take the emphasis from the sculpture. The other trade off of the slightly increased DOF is that the foreground foliage on the right is not completely out of focus, as at f1.4, but merely soft and more distracting. This image is the only one of the four I would reject.

Essential Aperture Skills by Thomas Kachadurian

At f5.6 all of the details in the front of the image are in focus while the garden within remains soft. This shows the beauty of the doors but loses the mysterious invitation of the image at f1.4. This might be the preferred image of the door’s craftsman.

Essential Aperture Skills by Thomas Kachadurian

At F11 the whole scene is unified. The door is still slightly sharper and has a degree of near far separation. Although soft, the garden inside is detailed and inviting. This image becomes more of a story of the whole garden, the inviting door and the sunlight within.

THE HOMEWORK ASSIGNMENT: Choose one or more scenes and make the same sort of test images I have here using your camera and your lenses. You will notice that, although my work is mostly with people, all of my examples are of static subjects. When learning to master aperture and depth of field it is important to start with subjects that stay put. As I did in all of these examples, use a tripod to eliminate camera movement as a factor in your results. When learning aperture basics it is best to keep the variables to a minimum. Even a photographer who has no interest in landscape photography will benefit from practice with fences and flowers and other things that don’t move.

Aperture must be used to completely control how a camera and lens will record an image. At larger openings, smaller f-numbers, a lens will have shallower depth of field. At smaller openings, larger f-numbers, more will appear in focus. But there is no correct amount of depth of field. There is no ideal aperture for any specific photograph. Rather photographers must learn to use the range of apertures to create images that match what they see in their minds. The examples above are just a few practical applications of aperture choice. In future posts I’ll explore more elements of photography where aperture choice is critical, and how to use aperture to make photographs that match your vision.

Olivia's Senior photograph by Thomas Kachadurian

Olivia at f1.4. It’s not super shallow because she’s more than 10 feet from the camera

This entry was posted in Photography and tagged , , , , .