The origin of the development of AF autofocus technology
Going back in time, students will find that manual photography technology is very complicated and must rely on manual metering, manual focus, self-winding, etc., which are widely used The results of human labor are often error-prone. Especially important scenes, once missed, cannot be repeated, so the quality of the photographer becomes an important factor in the success of taking pictures during this period. With the development of large-scale mechanical automation in the 1950s and 1960s, more and more people believe that automation is an indicator of the future world. The automatic metering technology and electric film winding machine that were completed in advance fully demonstrated that photography technology is indeed possible to move towards automation, and the most critical part of it is also the key point of the step that determines the speed of taking pictures, the 'autofocus system' has also become An indicator R&D project for various camera manufacturers at the time.
The world's first AF 35mm camera Konica C35 AF
The camera autofocus system can be traced back to the 1960s. In 1963, Canon exhibited a camera prototype with automatic focusing capabilities at the Cologne Expo (Photokina) in West Germany. The AF technology during this period was still quite primitive. Although the AE automatic exposure technology has gradually matured, the focusing capability was still bad. In 1974, Nikon also launched a prototype with autofocus capabilities; however, its design still relied heavily on mechanical structure, and its biggest shortcomings were large size and slow response. It was not until 1975 that the American Honeywell Company released the VISITRONIC AUTOMATIC FOCUSING SYSTEM, a practical autofocus element, also known as the VAF system. It is a pity that the American initiative actually brought about a revolution in the Japanese camera industry. In 1977, Japan's Konishi Roku Photo Industry Co., Ltd., which was later the predecessor of Konica Konica Co., Ltd., purchased the patent rights for this system improvement from the United States. , and in November of the same year, the Konica C35 AF, the world's first autofocus camera, was produced, becoming the world's first camera with autofocus capability.
． Principle of the first generation AF autofocus technology (passive)
Konica C35 AF is the first practical AF 135 traditional camera. It uses autofocus components produced by Honeywell Company and belongs to the first generation of passive autofocus technology. The basic principle of this technology is to analyze the reflection from the main subject of the scene as a reference index. The VAF autofocus system of KONICA C35 AF has a Mitsubishi mirror behind the two range-finding windows. The Mitsubishi mirror is responsible for refracting light to two reflectors. These two reflectors will project the image light to two mirrors respectively. In the image sensor at the bottom of the machine. An image sensor is a small computer composed of a photosensitive semiconductor (similar to a CCD) and an integrated circuit. The sensor uses the light and dark of the image, that is, the contrast, to distinguish the content of the image. During the focusing process of the camera, one set of reflective lenses is fixed, and its image is naturally fixed and becomes the control group. The other reflective lens moves back and forth. The amount of movement of this lens is calculated by a small computer and is directly reflected in the lens movement of the lens. Once the image sensors on both sides obtain the same image content, the autofocus is completed, which also means that the movement of the lens element has reached the correct focus position.
Schematic diagram of the passive focusing principle: two sets of sensors or CCDs, one of which is the control group. When the contrast of the two sets is displayed correctly, it means that the focus is completed.
The success of this system led to a revolution in the camera industry. Unfortunately, it was not the United States that made the biggest profits, but Japanese companies. Many Japanese companies used this design to successfully launch a variety of point-and-shoot autofocus cameras. From the 1970s to the 1990s, even most mini digital cameras and fully automatic digital cameras today use this principle to focus. Analysis: The advantage of this autofocus method is that the camera itself does not require a transmission system, so it consumes less energy and is low in cost. The light splitting system is simple and conducive to miniaturization.
It can fully autofocus when there is sufficient sunlight outdoors. Even under backlight or focusing on distant scenery, as long as there is brightness, this system can complete focusing.
Modern digital cameras use a large number of AF auxiliary focus lights to make up for the lack of brightness. The colors range from early red to the current cool green and blue.
However, since this system mainly accepts external light, it is called a 'passive' AF system. Because of this, when the light is too dark or the subject contrast is too low, VAF cannot work. In addition, For subjects with thin lines (such as telephone poles), VAF's autofocus is also more difficult and the accuracy is not high (nearest 1.1 meters to infinity). Therefore, point-and-shoot cameras and low-end digital cameras often cannot provide accurate macro shooting capabilities. This is also the reason. As for the problem of insufficient brightness when shooting indoors, later point-and-shoot and digital cameras often adopted designs such as ‘assistant focus lights’ to remedy the problem of insufficient light.