Depth of Field in Landscape Photography

Depth of field is a very important basic feature in photography in general and landscape photography in particular and a classic example of a too short blanket. It is significant both in the artistic aspect of the image and in its technical aspect and is the basis for choosing the focal point in landscape photography. What is depth of field, what affects it and how can we deal with the challenges it poses to us as landscape photographers - all in the next article

Large depth of field and edge-to-edge sharpness (Banff National Park, Canada)

If you have ever taken a landscape photo that you liked and discovered, after printing it enlarged, that its background or foreground looks a bit 'soft' and not 100% sharp, you are in good company. Don't blame your equipment and there is no need to rush to the stores to replace it. This is how optics work, and until they reinvent physics, we need to deal with it. The next article offers several ways to do this, but to do so, let's first understand what depth of field is and what affects it.

Depth of field is defined as the distance between the closest and farthest object in the image that is still obtained with reasonable sharpness. Okay, now for the explanation. When we focus on a specific point in the image, we are essentially changing the distance between the lens and the sensor so that the light rays coming from that point are focused exactly on the sensor. Unfortunately, the camera lens can only focus at one distance at a given time (hereinafter referred to as the focal plane). Anything closer or further away will no longer be in focus, meaning that the light rays coming from these points are focused in front of or behind the sensor. Luckily, this isn't so bad, because up to a certain limit, the human eye doesn't really notice this. Depth of field is everything within this limit, meaning that area of ​​the image where sharpness is still acceptable.

Depth of field is the distance before and after the point we are focused on that still looks sharp

The boundary between acceptable and unacceptable sharpness is determined by the diameter of the circle of confusion, the spot of light created on the sensor from a point that is not on the plane of focus. Where exactly this boundary passes (i.e. what is the size of the circle of confusion that is still considered sharp) is a complex question in itself, but when it is too large and visible to the eye, the point is outside the depth of field. Okay, and where do we as photographers come into the picture? Exactly here, because for a given diameter of the circle of confusion, the depth of field is a function of the aperture, the focal length of the lens, and the distance to which we focused it. This way we get a kind of control, at least some. And control, after all, is exactly what we like.

The depth of field for the relevant photography data can be easily found in dedicated tables and apps or on a scale that exists on some lenses. For each focal length and aperture we have chosen, we can know the distance before and after the point we focused on that will still be sharp (to a reasonable extent, as mentioned). That's good, isn't it? Of course it's good. Because that way we can plan where to focus and which area of ​​the image will be sharp. Portrait, animal or sports photographers, for example, usually prefer a shallow depth of field that creates good separation of the subject from the background. This is of course also possible in landscape photography, and sometimes we exploit this for artistic purposes, but most of the time the goal in landscape photography is to have as large a depth of field as possible and a sharp image from edge to edge. And this is exactly where the challenge begins.

Part of a depth of field table for a focal length of 24mm:

Focus distance	f/8	f/11	f/13	f/16
0.75m	0.58-1.07	0.53-1.30	0.50-1.50	0.47-1.84
1.0m	0.71-1.67	0.64-2.31	0.60-3.05	0.56-4.94
1.50m	0.97-3.84	0.81-10.53	0.74-∞	0.68-∞
2.0m	1.10-10.82	0.93-∞	0.85-∞	0.77-∞

Sharpness from edge to edge

Depth of field is a classic example of a blanket that is too short, requiring a decision about which part of the body we prefer to cover and which to leave exposed, or in our case - which part of the image will be sharp and which will be a little less so. The challenge is especially great in images that include a close and significant foreground and a distant and significant background, which often happens in landscape photography. For example, notice in the depth of field table above that if we focus to a distance of one meter at an aperture of f/11, the depth of field will be only 0.64 to 2.31 meters. Everything before or after will no longer be sharp, and the further we move away from this range, the more blurry it will be. Nevertheless, here are some methods of operation that allow us to utilize the full length of the blanket, and even extend it a little.

1. Aperture

With the help of the aperture, we can of course influence the amount of light that reaches the sensor. But, as already mentioned, the depth of field also depends (among other things) on the aperture key. The more closed it is (the larger the f-number), the greater the resulting depth of field. Usually, apertures of f/9 to f/16 are the most useful range in landscape photography to obtain a large depth of field. Why not to close the aperture even more, you may ask, f/22, for example? This is where another optical phenomenon called diffraction comes into play, which affects the sharpness of the image, so it is better to avoid it. Has this solved all the problems and brought the photographer a savior? Of course not. A closed aperture increases the depth of field, but it still does not guarantee a sharp image from near to far, and the further (or closer) you get from the focus point, the less sharp the image will be. And like everything in life, there are also disadvantages: when the aperture is closed, less light reaches the sensor, which requires a longer exposure (or higher ISO). In problematic light conditions, this requires the use of a tripod and great attention to moving objects. For landscape photography, however, the benefits usually far outweigh the cost, and at least allow us to use the entire length of the blanket, which is a good start.

Depth of field as a function of aperture: The narrower aperture in the lower figure creates a smaller circle of confusion for points 1 and 3, meaning a sharper image. Source: Wikipedia. By Diaphragm.svgderivative work: BenFrantzDale - Diaphragm.svg, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=11606603

2. The hyperfocal distance

The hyperfocal distance is the closest distance to which if we focus the lens we will still get reasonable sharpness all the way to infinity. That's the definition. The great thing is that focusing to the hyperfocal distance (H) ensures the greatest possible depth of field - from half the hyperfocal distance (H/2) to infinity. For a blur circle of a given diameter, the hyperfocal distance depends on the focal length of the lens and the aperture. For example, for a focal length of 24 mm and an aperture of f/11, the hyperfocal distance is 1.72 meters. If we focus to a distance of 1.7 meters we will get reasonable sharpness from a distance of 86 cm to infinity.

So far it sounds like every landscape photographer's wet dream. The good news are that you don't have to start putting numbers into complicated formulas. The hyperfocal distance can be easily found in dedicated photography apps or in tables available online. The less good news are that it is a good solution, even very good, but still not excellent. By definition, the sharpness required at the edges of the depth of field is only reasonable. Is that good enough? Sometimes yes and sometimes less so, depending on the image and what we plan to do with it. And what about the closest 86 centimeters (from the example above)? Sometimes they are no less important. If we return to our blanket for a moment, then using the hyperfocal distance stretches it to the limit. It is not always enough.

3. Using a Tilt/Shift Lens

This is an optically fascinating technique that is less common today but has been known since the 19th century. The pioneers of landscape photography of that era already used it to achieve the desired sharpness. Using a tilt lens does not really change the depth of field but the plane of focus, thus allowing you to get a sharp image from close to far away even with an open aperture. If you like, it changes the position of the blanket, say to cover along its diagonal. Changing the focal plane is not suitable for every situation and may in some cases lead to somewhat unexpected results, for example, a nearby tree may be sharp at its trunk but blurry at the top. Beyond the need for an additional (and often expensive) lens, the technique requires practice and understanding of the working method and the very non-trivial optics of this type of lens. In short, it is an interesting solution and, under the right conditions, very effective, but for most of us this option will probably remain on paper only.

The focal plane in a standard lens (top) and a tilt lens (bottom). The area highlighted in green simulates the depth of field.

4. Focus stacking

If you were offered a solution that allowed you to extend the blanket as much as you want, would you object? Probably not. Focus stacking is an uncomplicated technique that the digital age and the use of editing software make it relatively easy to perform and get a truly sharp image from edge to edge. It is especially recommended when we are shooting from a very short distance to an element close to the camera. To do this, you have to take several photos on a tripod at different focus distances without moving the camera or changing the exposure settings and then combine them in the editing software. This technique is less suitable when there are moving objects (branches, leaves, flowers, etc. and strong wind, for example, can create a problems) and it requires familiarity with editing software (recommended regardless), but beyond that, in combination with a closed aperture, it provides the most perfect solution and the greatest true depth of field. In short, it is recommended to learn and experiment with it (it is less complicated than it may seem).

Using the focus stacking technique allows sharpness from a few centimeters to infinity (Tuscany)

In conclusion, depth of field is a complex and important issue that often requires us to make decisions based on the needs in the field. Our ambition as landscape photographers is usually to extend it as much as possible, and as we have seen, there are several ways to achieve this, each of which has advantages, limitations, and disadvantages. The goal is to choose the approach that best suits the situation and the desired result. A good understanding of the subject and the tools at our disposal will help us implement an appropriate focus policy that will ensure that the important elements in the image are sufficiently sharp and thus achieve a result that satisfies us. More on that in the next article on the focus in landscape photography.