Sharp pictures: Everything you need to know about image sharpness

Caption: For a picture to be effective, the focus must be exactly where the subject or focal point is in the composition.

How do professionals manage to make their pictures look razor sharp? One might assume that they use an expensive camera with a high-resolution sensor. This may be true in many cases, but the use of a professional camera is by no means the decisive reason for perfect sharpness. On the contrary: even the most expensive technology can produce blurred images. Conversely, you can also capture high-quality images with inexpensive entry-level cameras. We'll tell you what it takes to take pictures that inspire.

Image sharpness and the RAW format are particularly important. We want to take a closer look at the aspect of image sharpness here. We will look at the various ways of increasing the sharpness of your images or eliminating sources of blur from the outset.

Depth of field: mastering the game of sharpness

Depth of field refers to the spatial depth at which the targeted objects in the image are in focus. On the one hand, the depth of field can be influenced by the aperture of your lens: the wider the aperture is open (e.g. f/2.8), the shallower the depth of field, i.e. an increasingly larger part of both the foreground and the background will be out of focus. On the other hand, the further the photographer closes the aperture (e.g. f/16), the greater the chance that the images will be sharp from front to back - an ideal setting for landscape photography.

However, it is also important how far away the camera is from the subject. The smaller the distance, the shallower the depth of field - a particular challenge for macro photographers. If insects or flowers are only a few centimetres away, the depth of field range is negligible even with the aperture closed.

Aperture, shooting distance and focal length

Caption: When photographing with wide-angle lenses, it is easier to capture the entire scene in focus.

The focal length also influences the depth of field. The wider your focal length (e.g. 24 mm), the more depth of field you will achieve in the image. It is therefore usually very difficult to crop an object in front of a blurred background with a focal length of 24 mm or shorter. With telephoto lenses, on the other hand, it is comparatively easy to crop in front of a blurred background - even at medium apertures of around f/6.3, making these focal lengths ideal for portraits and animal photography, for example.

In principle, the photographer has three parameters to control the depth of field: the aperture, the shooting distance and the focal length. It therefore ultimately depends on the lighting situation, the camera position and, of course, the composition of the image as to which method is best suited to the situation in question.  

• The easiest way is to open and close the aperture. Portrait photographers, for example, often work with an open aperture in order to focus only on the eyes and immerse the rest in a soft blur (bokeh). This shortens the exposure time, which makes hand-held shots easier. However, this requires a lens that is as fast as possible, such as an 85 mm f/1.2 - a first-class and classic portrait focal length.

• You can also limit the sharpness by moving closer to the subject. This makes the image section significantly smaller. Important: Pay attention to the image composition when shooting from a reduced distance. Even small details could negatively affect the overall composition.

• Changing the focal length is a third option - as a general rule, the longer the focal length, the shallower the depth of field. With a macro with a focal length of 100 mm and a close focusing distance, the depth of field is only a few millimetres.

2. perfect focus: From manual focus to the everyday helper autofocus

Caption: Modern cameras offer very helpful and precise focus modes such as eye autofocus. However, this can reach its limits when photographing through glass.

For an image to look sharp, the focus must be in the right position in the shot. While in genres such as landscape photography, an image should usually appear sharp from front to back, other photo subjects require a significantly smaller focus area. One example of this is portrait photography. Here, the model does not have to be completely in focus - as long as the eyes are in focus, the image will appear sharp to the viewer. What is important is that the focus is placed precisely.

There are basically two approaches to perfect focusing: Either you focus manually - i.e. by hand - or you let the technology take over and use the (preferably intelligent) autofocus. As with all technical decisions in photography, there are advantages and disadvantages as well as typical areas of application for both options.

Sharpness at the touch of a button: autofocus

Autofocus is one of the most useful camera functions - both for beginners and professionals: those who are just getting to know their camera are already well occupied with the exposure settings - and are therefore happy if they don't have to worry about manually positioning the focus. And professional photographers are also dependent on fast and precise focusing, depending on the subject: Without the help of the camera, even sports or wildlife photographers, for example, would sometimes bring home a significantly lower yield of usable images.

The autofocus modes at a glance

Autofocus has significantly changed the development of modern cameras. The ability to focus at the touch of a button has led to a much wider audience learning to take pictures. However, like any automated system, autofocus does not work flawlessly and sometimes needs a little help. To this end, digital SLR cameras and mirrorless system cameras offer a variety of autofocus modes that you can switch between depending on the situation and subject.

Many models offer a fully automatic mode, which is certainly very convenient for beginners. However, the chances of a razor-sharp image are increased above all by choosing the right basic settings. The most important ones are If the subject is moving, it is best to shoot with continuous autofocus; if the subject is relatively stationary, switch to single autofocus.

On many camera bodies, there is a rotary switch near the bayonet that can be used to switch between the AF modes: "S" stands for single autofocus, "C" for continuous, i.e. continuous autofocus for moving subjects, and "M" for manual focus. With other cameras, the mode must be set via the camera menu.

Manual focusing: When it is better to focus yourself

The autofocus of digital cameras has become much more precise and faster in recent years. Nevertheless, photographers still prefer to focus themselves in some situations. Intelligent assistants help them to do this.

In macro photography, it is often easier to work creatively with manual focusing: A slight turn of the focusing ring on the lens is enough to shift the focus from the pistil of a flower to the dewdrops on the edge of a leaf, for example. With more abstract subjects, the autofocus is less likely to know where the photographer wants to place the focus in the composition.

In addition to the creative possibilities offered by manual focusing, there are also situations in which there is no other option because the autofocus fails: in low light, for example, or when the subject offers little contrast, the autofocus sensor finds it difficult to find the clear contours it needs to focus.

The automatic system also has a hard time taking photos through grass, leaves or panes of glass - which can also be tricky for creative portraits. In such cases, it is better to switch to manual focus and position the lenses yourself by turning the focus ring.

Focus peaking & co: intelligent assistants for focusing

Assessing the focus on the small camera display or viewfinder is one of the biggest challenges when focusing manually. In analog photography, higher-quality cameras still had a "crop indicator". This was a focusing screen in the middle of the viewfinder that showed defocused areas slightly offset by opposing halves. To focus on a house facade, for example, a clearly recognizable outline was sought, such as a window frame. The sectional image indicator was positioned above this and then the focus ring was turned. If the two sectional images in the viewfinder coincided without any offset, the subject was in focus. The split-image indicator is still sometimes used today - for example in modern analog or digital rangefinder cameras.

Some mirrorless system cameras are equipped with a "digital split image" that is modeled on this split image indicator. However, one disadvantage of both the original and the digital replica is that only subjects that are in the center of the image can really be judged well.

A technique that is also known from analog cameras and video cameras is therefore much more popular: "focus peaking". It highlights high-contrast edges in the viewfinder or display in color. As the high-contrast edges are also the sharpest, this is a very good way of assessing the extent of the depth of field in the subject.

Another simple method of assessing sharpness is to enlarge the relevant image section to 100 percent. With this magnifying effect, the focus check takes a little longer, but the result is more accurate. And with subjects such as landscapes or still lifes, time is not a limiting factor anyway.

Focus stacking and hyperfocal distance

Especially in macro and product photography, photographers are faced with the challenge that some objects cannot be consistently in focus in a single image. This is where focus stacking comes into play, in which several images with different levels of sharpness are combined on the computer. To do this, several individual shots are taken with a slightly shifted focal plane. A macro rail, which is attached between the camera and tripod and with which the focal plane can be slowly moved through the image using an adjusting screw, is an aid for this.

Landscape photographers also attach great importance to the greatest possible depth of field: the aim is to capture breathtaking landscapes completely in focus to allow the viewer to lose themselves in the details. The magic word is "hyperfocal distance": it describes the distance at which the focus must be set in order to capture the largest possible subject area in sharp focus. The close-up point should extend far into the foreground, while the far point, up to which everything appears sharp, should extend to the horizon. If the focused point is further away than the hyperfocal distance, the depth of field shifts to infinity in some cases and is therefore lost. This sounds complicated, but you can easily determine this value with the help of depth of field calculators. It is best to make a note of the hyperfocal distance at f/16 for your favorite focal lengths, because then the depth of field is extended far without the diffraction blur of a closed aperture clouding the image impression too much.

How the aperture influences the depth of field

Caption: The open aperture makes the woman appear sharp, while the field of flowers in the foreground and the trees in the background are blurred.

The aperture controls the amount of light that reaches the sensor but, as already mentioned, also influences the appearance of a shot: with apertures from f/11, even expansive subjects can be captured sharply. With a more open aperture of f/2, the area in focus shrinks and large parts of the subject are rendered softly and without contours - a creative advantage: playing with sharpness and blurring is only possible with an open aperture - a particularly important approach for setting creative accents. It is the easiest way to play with the depth of field in a picture and is also suitable for those who are just starting out in photography. We will therefore take a closer look at the effect of the aperture on the sharpness in the image.

In photographic practice, the influence of the aperture on the depth of field is just as important as controlling the amount of light. How wide you open or close the aperture depends on the subject and the desired effect.

Open aperture: f/1 to f/4

If a subject is to be cropped against a blurred background and the foreground is to be artfully blurred, use an aperture that is as open as possible, such as f/2. The open aperture ensures a small area of sharpness in the image, making it easier to crop your subject from its surroundings.

Medium aperture: f/8 to f/11

In many cases, the medium aperture delivers the best image quality. It brings out the best in your subjects. With an aperture of f/8 to f/11, you can achieve a medium depth of field and - with sufficient light - you can still take pictures with fast shutter speeds. This combination produces the best optical results in terms of sharpness.

Closed aperture: f/16 and more

To maximize the depth of field, select a closed aperture - preferably f/16. Wide landscapes in particular will appear sharp from front to back. You can close the aperture even further, but this will result in diffraction blurring due to the small aperture opening. As a result, details in the image are lost and the entire shot often appears slightly blurred and flat.

The right aperture for your photo situation

Portrait photography

Caption: In portrait photography, it is not necessary for everything in the picture to always be in focus - it is important that the point of focus is on the eye. Here, for example, the model's ear is already outside the depth of field.

Portrait photographers, for example, love an open aperture because it reduces the depth of field so much that only the person is in focus. An unsteady foreground and background are then blurred and do not distract from the actual subject.

Macro photography

Caption: Larger apertures such as f/16 help to keep small subjects completely in focus. Macro photographers sometimes use several shots with different points of focus, which are then combined to create an image with a greater depth of field.

Macro photography, on the other hand, tends to be stopped down in order to capture a completely sharp image of a beetle, for example: Due to the small distance to the subject, the depth of field at open aperture is then in the millimeter range.

Landscape and architectural photography

Caption: A larger aperture such as f/11 guarantees that the entire scene is captured sharply in the shot.

Landscape and architectural photographers also like to stop down, usually to f/11 to f/16. If the focus is then hyperfocal, expansive subjects can be captured in great detail. Stopping down even more would further increase the depth of field, but would result in an overall softer, blurrier image. One phenomenon caused by the "negative space" behind the aperture is the so-called "diffraction blur". It is more pronounced with a closed aperture than with an open one. It also depends on the design effort and manufacturing quality at which f-number a lens delivers the best imaging performance.

General tips on the interaction of sharpness and aperture

As a general rule, the edges of the image often appear darker when the aperture is open (vignetting) and color fringing (chromatic aberration) can reduce the sharpness performance. Resolution and imaging performance are generally best at medium apertures. From aperture f/16, diffraction blurring leads to losses. If you don't want to create any special effects, it is therefore best to use an aperture of around f/8 - a good way to remember the photographer's saying "The sun is laughing, aperture 8".

There are two things to bear in mind when experimenting with the aperture: With some lenses, the focus range can shift when you stop down or stop up. When focusing manually, it is therefore advisable to check the focus again after changing the aperture setting. Also good to know: The image preview is not always generated at the set aperture (working aperture). This applies in particular to SLR cameras, whose optical viewfinder requires the bright light of the open aperture. In this case, the photographer must press a special "stop-down button" in order to be able to correctly assess the depth of field in advance. Although this is not necessary with Live View or an electronic viewfinder, in certain modes the preview may still show the subject with the aperture open. To switch to the working aperture and check the focus, it is often sufficient to press the shutter release button halfway. If this is not the case, it is best to assign the "Stop down" function to an FN button.

Practical tip: Aperture priority

If you want to experiment with the aperture, we recommend the aperture priority shooting mode. Fully manual photography requires experience. The (semi-)automatic shooting mode "Aperture priority" is easier to use. This gives you control over the depth of field without having to worry about the brightness of the image. This mode is usually marked "Av" or "A" on the setting dial. "Av" is the abbreviation for "Aperture".

You can find out more about aperture, shutter speed and ISO, the other two factors in the exposure triangle, here.

Conclusion

Sharp images require practice, technical understanding and a feeling for the moment. Not every subject needs to be in focus from front to back. There are no limits to creativity and photography allows us to experiment with the possibilities offered by photographic technology. This turns an everyday situation into an extraordinary moment that can be printed or exposed to perfection. For example, ultra HD paper and acrylic glass are ideal for monumental landscape shots, while subtle portraits can be enhanced in a variety of ways on high-quality fine art paper.