What is Depth of View (DoF)?

1. Introduce

Depth of field refers to when the lens focuses on a certain point in the subject, which can be clearly pictured on the film, because "clear" is not an absolute concept, so before and after a certain range of scenery can be recorded more clearly. The sum of this range is called depth of field. It means that as long as the scenery within this range can be clearly photographed.

2. The principle of depth of field

Light from parallel axes, after passing through the lens, will converge through the focal length of the lens. And the light that passes through the axis doesn't deflect. But whenever either route hits the lens, it changes direction and meets at the right point. The Sensor is placed in the imaging area.

Objects at different distances have different imaging positions behind convex lenses. In the figure below, points 1 and 3 will be blurred due to the fact that the image is in one area on the CCD. The so-called depth of field is the area surrounded by points 1 and 3 under clearly identifiable conditions.

       Remark1：Fuzzy imaging of 2 points on CCD

Because the human eye has limited area resolution, when the length and width of a color is less than about 1/2800 inch, it cannot distinguish the area of the color, so the area is only one point to the naked eye. For example, the imaging area of point 1 is smaller than the area that can be distinguished by the naked eye, then we will feel that point 1 is also clear.

So when the convex lens is smaller in size, or partially blocked by the camera aperture, the image can still be clearly formed behind the mirror. The original point 1 imaging should be fuzzy, after reducing the aperture action, the fuzzy point formed on the CCD will shrink, so that the original should be fuzzy part, become clear. To sum up, reducing the aperture can increase the depth of field, and the aperture value is the ratio of the effective aperture of the lens to the focal length of the lens.

3. Factors affecting depth of field

• The size of the aperture: The smaller the aperture, the greater the depth of field; The larger the aperture, the smaller the depth of field.

         

            F1.4 Large aperture, minimum depth of field

            F22 Small aperture, maximum depth of field

• The focal length of the lens: The longer the focal length of the lens, the smaller the depth of field; The shorter the focal length, the greater the depth of field.

• The distance of the shot: The greater the distance, the greater the depth of field; The closer the distance, the smaller the depth of field.

• Object quality requirement: It is mainly manifested as the diameter of the dispersion circle, before and after the focus, the light begins to gather and spread, and the point is affected to become blurred, forming an enlarged circle, which is called the dispersion circle. If the diameter of the dispersion circle is smaller than the discerning ability of the human eye, the blurring resulting from the actual influence is not recognizable within a certain range. This unrecognizable dispersion circle becomes the admissible dispersion circle.

          

4. The meaning of depth of field

Depth of field has a great relationship with image performance. For example, when shooting portraits of people, narrow depth of field will bring a very blurred background, so that clear figures can be highlighted, in many large scenes of scenery photography, large depth of field can obtain broad clear images from near to far, to achieve pleasing effects.