Sharpness and focus
If in the human eye, accommodation occurs by modifying the focal length of the lens, in a camera, focusing is achieved by lengthening the distance between the lens and the sensor. To make focusing easier, the oldest devices had distance measuring tools. Recent devices are equipped with extremely precise autofocus systems. – Photo courses / The fundamentals of shooting (EYROLLES)
Focusing (MAP) in photography is simply the operation which will allow you to adjust the sharpness, particularly in photography because poor focus can generate blurry photos which can be considered of poor quality. When taking a photograph we generally seek “perfection”, so that our photo is as clear as possible.
In photography, it is possible to choose using a camera or a telephone the shot that you want to make sharp by adjusting the sharpness zone. The sharpness area represents the distance between the first sharp plane and the last sharp plane of the image. In this area the subjects are sharp and outside this area they are blurry. We talk about depth of field when the extent of the area of sharpness appears in a photo. When the depth of field is small, the area of sharpness is only slightly extended.
In a photographic camera, focusing is achieved by moving all or part of its optical system (the lens). Unlike the human eye, an objective contains several lenses that do not distort. So, to focus, all of these lenses are moved relative to the sensor. In the eye, sharpness is obtained by the action of the ciliary muscles on the curvature of the lens: this is accommodation.
Example of focusing only on the foreground
Example of a “completely” sharp image
Focusing can be done automatically or manually. For manual mode, it is generally configured at the camera lens. Consider the case of modern cameras. They have so-called automatic focusing or also called “autofocus”. If the device is sufficiently advanced, it is possible to choose the focus area; you just need to touch the screen with your finger to the desired location to focus (e.g. smartphones). It is still very important to master your camera well in order to understand the reactions of the autofocus when given subjects to focus on.
The collimator is a shape displayed in the middle of the screen and lights up when focus is achieved. This is precisely used to choose the area of sharpness and do the autofocus.
All the vagueness is not without interest. In photography or cinema, a blur effect can be desired and controlled; it will be called artistic blur. Indeed, the search for blur can enhance images. In certain cases, however, vagueness cannot be avoided for material reasons.
There are several causes that can result in a blurry image and these factors can be used to generate artistic blur. First of all, as we have just seen, poor focus causes blur in photos.
Lighting is also a key factor in creating a successful image, we talked about in a previous article.
The absence of light can therefore cause blurry photos. The shutter speed becomes low and it becomes difficult to freeze the movement handheld.
The aperture setting of the iris can also generate blur. If you choose a large aperture, reducing the area of sharpness will have the effect of generating blur in the image, outside the area.
In photography, some artistic blurs are also created by movement. For example, motion blur is the blur produced by moving the lens while taking the photo. Conversely, motion blur is the blur visible in a photo due to movement of the subject photographed and not to the instability of the camera.
To conclude, in photography it is important to have quality and, above all, usable renderings. Focusing is the most important thing to do before capturing photos. Vagueness can be desired and controlled or to be feared. Many parameters must be checked such as lighting, focus, collimators or even the diaphragm.
Today, many cameras have an autofocus function that allows you to focus automatically and choose a subject in the image on which to focus the focus. This function is carried out digitally based on the analysis of the image perceived by the device.
