depth of field – what is that?

The term depth of field describes the extent of the sharp area in the photo. The word depth of field should therefore be taken literally. It is a measure of how deeply into the photo (or correctly formulated: into the object space) all objects are sharply depicted. A shallow depth of field means that only objects in the foreground are really sharp, while the background is blurred. Conversely, a large depth of field means that both the foreground and background are in focus. You must therefore ensure a low depth of field if, for example, you want to make a portrait.

Then only the person is interested, the background is uninteresting. However, if you want to photograph a landscape, it is of course desirable to provide a large depth of field so that the landscape is as deep as possible in focus. In macro photography, on the other hand, a strongly blurred background is more desirable again so that the viewer’s gaze is fully focused on the object – for example, a bee on a flower.

It is only about the bee and the veining in the wings. The brook, which perhaps flows half a meter deeper under the flower, is of no interest and can rise in the blurred background. If you place the object skillfully, then you can direct the viewer’s gaze to the object with an appropriately adjusted focal length and depth of field. To do this, you must place the depth of field as close as possible to the main motif. This makes the foreground and background less sharp and the object is completely in the sharp area. This is called selective blurring.

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depth of field – how do I do that?

The means by which you can influence the depth of field is the aperture. A large aperture provides a shallow depth of field, a small aperture provides a large depth of field. Please note that in photographer’s jargon a large aperture means a large aperture and thus a small number of apertures. f/2.8 thus provides a small depth of field (background blurred), while f/16 provides a large depth of field (background sharp). For the example of a portrait shot mentioned above, you have to set a small aperture number so that the person stands out from the background. It’s called exemption.

The same applies to the bee on the blossom. It stands out against the stream flowing underneath if you set a small aperture number (photograph with a large aperture, as a photographer would say). For our landscape, on the other hand, you have to set a large f-number so that as much of it as possible is sharply displayed. A small aperture ensures of course that little light falls on the sensor. Therefore, don’t forget to set the shutter speed longer and increase the ISO value if necessary.

However, higher ISO values have a negative effect on the image quality, so that you should rather use a tripod. Of course, most cameras have an automatic function (“Av” is the name of this setting in Canon, for example), where you only have to worry about the f-number and the camera then automatically adjusts the shutter speed and ISO value – but you should still keep an eye on what your camera is setting, because that’s not always correct.

The depth of field is an important design element. With a small depth of field on the one hand, objects (especially people in portrait photography) can be lifted from the background (released). On the other hand, with a large depth of field, all objects, including the background, are sharply focused (important for landscape shots). The depth of field is controlled by the aperture. A small f-number provides a small depth of field, a large f-number provides a large depth of field.

depth of field for landscape photography

aperture & depth of field – simply explained

The aperture – what is that?

When taking a photo, there are three main parameters that affect the photo. The shutter speed, the ISO value and the aperture. The aperture is a device built into the lens that controls the amount of light coming in. The measure of the aperture is given as the f-number. It is the ratio of the focal length to the aperture (cross-sectional area through which the light passes) of the lens. Large f-numbers stand for small apertures and small f-numbers for large apertures (you can remember: the larger the f-number, the more “aperture there is”, the smaller the aperture and the less light passes through).

An f-number of 2.8 therefore means a large aperture and correspondingly much light incidence, an f-number of 16 exactly the opposite. The f-number on lenses is always indicated in the form 1:f-stop. So if it says 1:2.8 on a 100 mm lens, it means that you can set a minimum f-number of 2.8 for a 100 mm focal length. Mostly the aperture is built as a so-called iris diaphragm. Circularly arranged blades are shifted against each other in such a way that the incident light beam becomes either smaller (large f-number) or larger (small f-number).

Interplay between aperture and shutter speed

If you arrange the different f-numbers in order of size, you get the f-stop series: 1 – 1.4 – 2 – 2.8 – 4 – 5.6 – 8 – 11 – 16 – 22 – 32. Along this series, the amount of incident light is halved with each step. So at an f-number of 5.6, only half as much light hits the sensor as at f-number 4. The value of the shutter speed must therefore be adjusted accordingly: the larger the f-number, the slower the shutter speed (at a constant ISO value). Common usage in photography usually uses the word aperture to refer to the opening of the aperture. “Large aperture” in technical jargon therefore means large aperture opening. This can easily lead to confusion, because a large f-number correctly corresponds to a small aperture.

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The aperture – What can I do with it?

The most important creative tool over which aperture has a great influence is depth of field. Depth of field is a measure of how far the area in focus extends into the photograph. For example, only the foreground may be in focus, while the background is perceived as a blurry, possibly colored area. This option of image composition would be used for a portrait, for example (this is also called “cropping”).

On the other hand, if you want to photograph a beautiful landscape, let’s say a stream, then you want that stream to be in focus as deep into the photo as possible, so you want to achieve the greatest depth of field possible.

What you need to do is to set the aperture correctly! Small f-numbers mean shallow depth of field, large f-numbers mean large depth of field. So for our portrait above you would choose a very small f-number (1 or 1.4), for the course of the stream rather 11 or even 16 if the light conditions allow it; because as I said, the larger the f-number, the longer you have to expose. So a large depth of field usually requires the use of a tripod. The correspondingly longer shutter speeds also lead to motion blur worth seeing, especially with flowing water.

The aperture is one of the three basic parameters with which you can influence the image composition. It controls the amount of light that falls on the sensor and the size of the light beam. It is the most important control when varying the depth of field.

Important parts of the camera: The aperture