Ask the master to introduce SLR lens camera focus principle?
3, focusing means
????Canon in the AF era, there is a big thing, that is, change. FD before the direct abandonment, replaced by the later EOS mouth. EOS mouth is the biggest feature of all-electronic contacts. Because there is no transmission structure, so it uses a lens motor. Here we classify the focusing means.
????(1) body motor. Body motor is installed in the camera body inside a motor, through the fuselage signal, direct the motor rotation. The fuselage bayonet has a screw cap like a small one-shaped mouth, the lens with a screwdriver with the same knife, the lens hit the fuselage when the body of the screw cap is a font with the lens Screw knife the same knife match. The power of the fuselage motor through the lens screwdriver linked to the lens inside the multiple transmission structure, and finally command the lens of the focus lens before and after the move. As early as the Minolta, Nikon, Pentax are this way of focusing.
????(2) lens motor. Before that Canon switch, because the eos mouth no drive screwdriver, only the transmission of electronic signal contacts, so Canon put the focus motor to the lens. The body only need to issue a drive command, the lens motor can be rotated by instructions. At present, everyone has a lens of the lens.
The difference between the two focus means is obvious. Body motor do not know why, the sound is very large and the lens motor sound is very small, the fuselage motor due to the cumbersome transmission structure so the focus speed is relatively slow and the lens motor is generally faster, except for low-end lens motor. Lens motor as the motor itself to take up the volume, so the general lens of the lens head is relatively large.
But for the average user, are enough, in addition to the sound outside the sound is not much difference.
1, why should the lens focus?
????This is an optical problem. We have done this experiment before, as shown. When the position of the object is at position 1, if the image falls just on the photoreceptor at this time, the clear image will be in the image 2 when the object moves to position 2. At this time the lens must correct the optical path, so that the most clear imaging is still falling on the photosensitive element, so need to focus. Focus is to correct this optical path, by changing the overall refractive index of the lens to ensure that the distance, because the back of the lens to the photosensitive element of the distance is fixed.
