In landscape photography, as in other photographic genres, focus is essential. In landscape, in fact, the photographer’s will is often to have everything in focus and as clear as possible. Both the foreground and the background must be very clear and to achieve this we must be sure that we have set the right aperture, focus distance and focal length.
Aperture and the depth of field
The aperture (f /) defines the depth of field in the photos we take: a narrower aperture allows us to obtain a greater depth of field with the same focal length. The focal length is the second element that influences the depth of field: with the same aperture, increasing the focal length (for example from 24 to 35mm) the depth of field decreases. The third factor affecting focus is the sensor’s CoC (Circle of Confusion).
Without going into the calculation of this factor, it is sufficient to know that a sensor with many pixels will be denser and therefore “capture” a greater number of details. For this reason it is also easier to observe a difference in focus from one pixel to another. In a very resolute sensor, it is easier to detect small changes in focus, so you need to pay more attention.
A fourth and last factor influencing the focus is the focusing distance: if we focus very close to the lens, the background will be out of focus (with a smartphone for example.) Whilst focusing on a subject in the middle of the frame, we will most likely not notice out of focus areas. The focus distance is one of two factors, together with the aperture, which allows you to determine the maximum extent of focus: hyperfocal.
Hyperfocal: maximising the depth of field
The maximisation of the depth of field is obtained by acting on four fundamental factors: focal, Circle of Confusion, aperture and focus distance. Since in landscape photography the composition should be the main factor according to which the decisions are made, the focal, which directly influences the composition, will be a given priroity. The Circle of Confusion will be another fact taken into consideration as it is defined by the sensor of your camera. Therefore, the aperture and the focusing distance remain as unknowns that we can control to have the desired depth of field.
We will talk about hyperfocal in depth in a separate article, therefore here it is just sufficient to know that there is a focus point and aperture for which the depth of field is equal to half this distance up to infinity. You can use mobile applications, such as PhotoPills, to calculate this value, or you can rely on experience and empirical evidence in the field.
For example, if you do not have a close-up too close (more than 3-4 meters) you can focus indefinitely even in autofocus and closing at f/8 or f/11 you will not have problems with depth of field. But if the foreground is closer, things get complicated ..
The steps for perfect focus in the field
Since very often during landscape photography you shoot during sunrise or sunset where the light is low, focusing is more difficult as Autofocus doesn’t work very well with low brightness. If the foreground is not close we can try to focus infinitely; if the AF works we can rely on this, but if the light is too low we will have to focus by hand. In this case, it is important to avoid turning the focus ring all the way to infinity as the photo will certainly be out of focus at full scale.
The infinity focus is perfect just before it’s full extent: we can find this point by zooming in live view and checking that a distant subject (at least 10 meters with a wide angle) is well defined, or we must find the exact point of focus to infinity when there is light so as to find the same point even in the dark or in low light. If, however, the foreground is very close, we must estimate the distance of the foreground and focus at about this distance or a little more: let’s take a test shot at f/8 of /11 and check on the screen, by zooming, that the photo is at correct. If the foreground is out of focus, while the background is in focus, we can take a second shot focusing on a point closer to us. In the opposite situation, that is, if the foreground is in focus but the background is out of focus, we must try to focus a little further away. If we cannot find a point where both the background and the foreground are in focus, we can only try to close the aperture more (pay attention to diffraction!) or reduce the focal length.
Even moving slightly away from the foreground naturally helps, but it will be necessary to re-evaluate the new composition. With these few steps you can manage practically every situation. The core advice is to understand the relationship between focal length, focus distance and aperture.
Focus in Landscape Long Exposure
Long exposure and landscape photography in general, have peculiar characteristics to be taken into consideration. The first thing to keep in mind is to focus before inserting very dark ND filters: after inserting them it will be more difficult to accurately determine the focus point due to the low light that reaches the sensor/viewfinder. Once you find the right focus, make sure that the AF is disabled so as to avoid an accidental change of focus. We always check the focus after each shot (both in the background and in the foreground) through the zoom of the preview of the shot on the display, so we will be sure that it is constantly correct.
Knowing the hyperfocal is important, but it is even more important to know the relationship between distance, aperture and focal length. If we focus at infinity and the foreground is out of focus we can achieve focus on the whole frame either by closing the aperture, or by using a wider focal length (wide), and moving away from the foreground. Very often not all these solutions are practical without limitations: it is therefore important to try several things in order to obtain the desired depth. If we are limited by focal length and have the possibility of moving backwards, then we try to close the aperture. If we cannot close the aperture we have to move away or use a wider focal length.