Focal length - what is it and what role does it play? Below we explain the relationship of this variable to angle of view and perspective. Experienced photographers will have no problem setting the parameter, but beginners may mistakenly interpret the role of focal length.

Focal length - what is it?

Focal length is the distance between the focal point and the main point of the optical system. The focal point is the point at which light rays intersect - initially parallel to the optical axis - after passing through the optical system. In the case of light rays converging, we speak of a real focal point. When the rays are spread out by the optical system, we have a virtual focal point.

The main point is the point from which the focal length is measured. Very thick and complex lenses have two main points.

In photography, focal length determines the angle of view of the lens.

Let's focus on how this parameter works in one of the most important issues for visual creators:

Perspective

Actually, the focal length changes the frame, but it doesn't affect the perspective. In zoom lenses, we can zoom in or out of the photographed object, which changes the scope of the scene. We can say that focal length determines the slice of the world that is captured. Of course, cropping or zooming in on an object using a wide-angle or digital zoom lens is a substitute for determining the image range.

In photography, there are also:

Prime lenses

Their greatest advantage is their high image quality when shooting up close. They perform very well even in low light. Their main purpose is portrait photography. Usually, in this case, the choice is made between two focal lengths: 35 or 50 mm. A narrower angle of view allows for good, attractive photos to be taken from a closer distance.

However, it is important to be aware that a prime lens affects the change in perspective in photos. This is due to the fact that when we want to zoom in on an object, we must physically approach it, which affects its representation and changes the viewing angles.

At the end of the article, we will return to the issue of portraits - taken with both prime and zoom lenses.

Now it's worth mentioning that in the case of prime lenses, autofocus is an extremely important issue:

Autofocus

Taking close-up photos requires high sharpness. The ability to automatically set focus is a key feature of the lens as it affects the quality of the photos taken. With a shallow depth of field, each mistake or oversight can ruin efforts to take a quality photo. Therefore, the choice of a prime lens should be combined with testing and a good assessment of the autofocus capabilities.

Returning to portraits:

Focal length in portraiture

We mentioned that prime lenses are ideal for taking portraits because of their good image quality when shooting up close. However, in different life situations, it may be useful to capture a person in a variable frame and different distances.

There are two basic focal lengths: 35 and 50 mm, the same as those chosen for prime lenses. For outdoor shots that show the whole figure, it's worth choosing a 75 or 135 mm focal length.

A significant problem may be the distortion of facial proportions. With a small focal length, for example, the nose or glasses of the person being portrayed may appear unnaturally enlarged and brought closer to other parts of the head, such as the ears. Therefore, before the main action, it is worth taking a series of test photos and recording which parameter best captures the person being captured.

Finally, it's worth noting one more thing:

Focal length in outdoor and studio photography

For outdoor photography and in large rooms, a higher focal length, for example, 105 or 135 mm, is suitable. In smaller semi-professional or amateur studios, a lower parameter will be better suited to the conditions and contribute to a more natural image of the photographed object.

Keep in mind that short telephoto lenses may unnaturally exaggerate the subject or object in the background, blur the background, and distort perspective.

To sum up: the choice of equipment, its technical and parametric capabilities must be preceded by an analysis of our needs and expectations of clients - customers. Many shops offer the opportunity to rent cameras, lenses, and other devices for testing. It's worth preparing a list of test tasks and recording notes from the tests to make a purchase that best covers the widest range of our future operational possibilities.