Discussion topic: the practical significance of photographic depth of field

According to the definition, the depth of field is the "acceptable clear range" that the focus extends back and forth.

In other words, when you choose a subject, the focus will fall on the subject. But in this picture, not only the focus is clear, but also the whole picture will be clear, but there is a clear range acceptable to the human eye before and after the focus. This range will vary according to the aperture, focal length and the distance between the photographer and the subject. There is also the concept of diffusion circle. When high definition is required, the diameter of the diffusion circle is required to be smaller, the acceptable definition range is smaller and the depth of field is smaller.

In fact, as a simple definition, it is difficult for us to understand the meaning of depth of field immediately. Moreover, just like cooking does not need to know how rice is grown, we only need to have a general understanding of this concept, and the most important thing is to know what kind of influence this concept will have on the photos we take, and how to implement this concept in some setting parameters we use in the shooting process.

As mentioned above, the difference in depth of field is mainly due to the different aperture and focal length used by the photographer, and the distance between the photographer and the subject changes. So to sum up, the main related factors of depth of field are aperture, focal length and object distance.

For the influence of aperture on depth of field, it is mainly that large aperture can get small depth of field and small aperture can get large depth of field. For example, in the case of the same focal length and object distance, the depth of field obtained by aperture F8 is definitely smaller than aperture F22 (both sides are reciprocal, and the greater the denominator, the smaller the score). The effect presented in the figure is that the clear range around the focus is smaller than that of F22 in the figure of aperture F8, so it can be clearly seen that the areas of the clear parts in the two figures are different. In all kinds of specific photography, we can often see it from still life photography and advertising photography. Although the pictures obtained are similar to others, the shooting of these items has certain requirements for the aperture, so it is closely related to the aperture.

The influence of focal length on depth of field is basically similar to that of aperture, that is, long focal length can get small depth of field and short focal length can get large depth of field. For example, when the other two parameters are the same, the depth of field obtained by a lens with a focal length of 300 is definitely much smaller than that of a standard lens with a focal length of 50. This is generally reflected in sports photography, wildlife photography and news photography.

In terms of object distance, a small object distance (the distance between the photographer and the subject) can get a small depth of field, and a large object distance can get a large depth of field. Under the same aperture and focal length parameters, the closer to the object, the smaller the clear range will be; On the contrary, the bigger it is. This is mainly manifested in landscape photography. When shooting close-ups such as small flowers and dewdrops, the depth of field will become smaller because of the close distance, while when shooting large scenes such as mountains, grasslands and the sky, the focal length is basically infinite, and the clear range will become larger, that is, the depth of field will become larger. If matched with the small aperture of the super wide-angle lens, it can be clear from a few meters to infinity.