The general principle of operation of a SLR camera has not changed for a very long time - a beam of light passes through the lens, is reflected through a mirror, is projected onto frosted glass, flips over in a pentaprism and we see the image in an optical viewfinder. When we take a picture, the mirror rises and a beam of light hits the matrix or film, thus forming the image that we saw through the viewfinder.
But in fact, in modern digital mirror cameras (CZK), everything is much more complicated. Modern cameras have a number of additional devices that few people realize:
- Metering sensor exposurewhich is at the pentaprism
- Pentaprism can be replaced by a pentaser
- Between the frosted glass and the pentamirror is a special transparent LCD display - in more detail here
- In modern central control centers in fact two mirrors
- The second mirror is suspended behind the main
- The main mirror has a special translucent window
- Between the mirror and the matrix there is a camera shutter
- Many cameras have a diaphragm control system in the mirror shaft
- The luminous flux is deflected by the second mirror down towards the autofocus system
- When you release the shutter, the second mirror hides, it is impossible to see
- The focusing system uses a sophisticated beam re-reflection technique to detect phase difference
It would seem that everything is simple, but you see how many additional difficulties. The picture below shows the general scheme of work of a modern central control center - it is clearly seen that the camera has both main mirror '121a' and additional mirror '121b'.
Modern CZKs have a special focusing system. The special module, which is located at the bottom of the main mirror, is responsible for focusing. Focus module listed as '132 AF sensor'. The light beam that passes through the lens is partially reflected at an angle of 45 degrees and directed to the '126' pentaprism, and partially passes through a special translucent window in the main mirror. The beam that went through the window of the main mirror reflected in an additional mirror and goes to the auto focus sensors. The auto focus sensor passes the beam through its special lenses, detects the phases and adjusts the focus.
When the picture is taken, the mirror rises, an additional mirror is superimposed on the main one, so that it is not visible. In this case, a ray of light through the open shutter hits the camera’s matrix. The photo above shows beam motion pattern for camera Nikon D2h.
I almost never met such an extended description of the movement of rays in the chamber, and after the breakdown of my D700 decided to write this article. The mirror shown here was taken from the camera. Nikon D700, you can easily consider the structure of the primary and secondary mirrors.
If you look at the mirror directly, as shown in the figure above, it is impossible to notice the second mirror. The figure below shows the mirrors on the side, the fastening mechanism of the second mirror and the second mirror itself are clearly visible.
The figure below shows the front and rear view of the mirrors. An additional mirror and a translucent window in the main mirror are clearly visible behind.
Separately, I will focus on the fact that when the mirror is raised, the additional mirror slams. The additional mirror at the back is covered in black plastic, like the rest of the main mirror. In the raised position, such a system does not transmit light that comes from the optical viewfinder in the opposite direction (actually skips).
Modern CZKs have a slightly different principle of operation than the old film SLR cameras. Basically, the difference is in availability second mirrorthat participates in the focusing system and transparent LCD display to project visual effects.
↓↓↓ Like ↓↓↓ - helping the project. Thanks for attention. Arkady Shapoval.