How many laws are there for big format?

? Sham's law is one of the most conventional laws in a large space. This is the pseudo-law!

? Sham's law means that when the object plane, the image plane and the extended surface of the lens plane intersect into a straight line, a comprehensive and clear image can be obtained.

? Sham's law only applies to make a face of the subject focus on the image completely, that is, from the nearest point to the farthest point of the subject, no matter which direction the face is in, it can be displayed completely and clearly. However, there is nothing you can do to improve the clarity of more than two faces at the same time. At this time, the aperture fit should be reduced.

? Introduction to Sham's Law

Sham's law means that when the object plane, the image plane and the extended surface of the lens plane intersect into a straight line, a comprehensive and clear image can be obtained.

Using Sham's law to shoot, you can keep fine details from the nearest grass and gravel to the farthest rocks and shrubs, which ordinary cameras and lenses can't do even with the smallest aperture. For an old and flexible large-format camera, as long as three planes converge, even the largest aperture can still get a large clear range. Because this law was first discovered by Austrian prosecutor Sham Frog in 1894, it is called Sham's Law or Shaughnessy's Theorem.

The so-called three planes of Sham's Law, namely, the object plane (scene), the film plane (rear group part) and the lens plane (front group part) converge on an imaginary point below the camera. The smaller the adjustment before swinging, the greater the swing amplitude of the rear group, the smaller the swing amplitude of the rear group and the greater the swing amplitude of the front group. When transporting samples, three planes intersect at one point, which can make the inclined subject get the maximum clear range. In fact, this technique of changing the focal plane position is different from the conventional concept of depth of field, and it has more flexible characteristics.

Based on "Sham's Law" and angle adjustment, a large format camera can take photos with extraordinary visual effects through translation, lifting, tilting and even vertical rotation.

Second, the technical points of Siam's law

Choice of camera. Sham's law can be realized not only by large format cameras, but also by some adjustable medium format cameras and some shift-axis lenses used by 135 cameras. Among them, monorail large-format camera has great advantages in adjustment flexibility. ?

Adjustment of the front group. The adjustment before the swing is very important to the coverage of the lens, especially the distant scenery is prone to "occlusion", so we should closely observe the effect of the focusing screen. ?

Adjustment of the back group. The adjustment of the back can also increase the depth of field of the inclined subject plane or change the shape of the image. Therefore, "Sham's Law" should combine the adjustment of the front group and the back group to obtain the maximum clearance range with the minimum coverage.

Third, the diagram of Siam's law.

? Let's look at the picture, but I don't want to make it more intuitive here, mainly because I want such a picture. There are many online. The following pictures, mainly from the perspective of the lens overlooking, also see the change of the clear plane when the lens is tilted. To really understand, it's best to have a machine in your hand to operate it and verify it against the pictures, so it's very clear. Sometimes it takes a long time for you to explain something clearly in theory. You may not be able to explain it clearly, but once you get started, you will understand it immediately. Hehe, of course, that also needs a little space imagination. It's just that I don't want to make everything clear here, and I can't make it clear. I can only use these pictures to express my understanding.

This picture shows the difference between a focal point and a clear plane. Siam's law says that there must be a "three-sided convergence line" in a graph. The angle of the lens is constant and the focal plane is constant, and this line is determined. Then, once the focus is determined, mathematically, a line and a point outside the line only determine a plane, and this plane is a clear plane. The clear plane of focus B is cut into two sections by the ground plane, one is the actual clear plane, and the other is only of theoretical significance.

? Imagine the actual situation. If there are three objects with different heights lined up in front of the lens at this time, and the aperture depth of field used is very small, it is impossible to see them all clearly without such a lens. But by adjusting the angle of the lens, all three objects fall in a clear plane, so the imaging of all three objects is clear.

? The above two pictures illustrate the change of the clear plane in different situations. It can be used as a reference in practical operation, and its specific function can be verified in practical operation. For example, in this picture with constant focal length, after a point is focused, the change of lens angle and the change of clear plane will be the way shown in the picture.

Furthermore, as can be seen from the above figure, the clear red plane can be said to extend from the front of the lens to infinity almost relative to the viewing angle of the red lens. This is also a unique means in large-scale landscape photography. Coupled with a small aperture of 22 or even 45 and a large depth of field, it is almost completely clear from the photographer's foot to infinity. This is beyond the reach of ordinary cameras.

What's the use of this rule? If you ask me, if you practice, the method is useless. Who is still meditating in the middle of the filming process?

5.Sham's law also has limitations. What are the restrictions? Speak with pictures.

? The above figure shows that there may be some restrictions in actual operation. The first is the back angle of the lens. Of course, we can't hope that the back angle of the lens can be 180 degrees. First of all, we must watch movies through the lens, right? If you can't see it, it's nonsense to adjust it again. This is the first limitation: according to the above picture, the lower edge of the back corner of the lens can be adjusted to be aligned with the lower edge of the film at most, and then the film can't be seen. Second, even if the lens viewing angle is 180 degrees, the maximum rotation angle of the camera front group will limit the adjustment ability. Needless to say, if the frame is adjusted too much, the light will be blocked. This is the second limitation. These are the two main limitations, and there are others. But under normal circumstances, such a big adjustment will not be used.