The SLR camera can’t focus automatically, what’s going on?

1. The focusing distance exceeds the minimum focusing distance of the lens

2. The camera is set to MF manual focus mode

3. The lens is set to MF manual Focus mode

4. Improper selection of the focus point of the telephoto lens causes bellows

5. There is no obvious separation between light and dark near the focus point, resulting in inability to achieve focus

6. Unable to focus due to too weak light

Content expansion:

1. For normal people, we have to mention the camera’s out-of-focus phenomenon. Out-of-focus refers to the phenomenon that the camera has indicated that the focus is accurate when composing and focusing, but the photos taken are still out of focus. There are many reasons for this: the vibration caused by the mirror popping up causes the camera position to shift, the body's autofocus module is aging and has errors, the lens contacts are in poor contact, communication failures, and the lens focus motor brake system failure.

2. The first reason is unavoidable regardless of autofocus or manual focus. Especially when using long focal length, large aperture, and close-range photography, due to the extremely shallow depth of field obtained, the camera will be slightly offset. Blurred photos will occur. In this case, you can only use a tripod to secure the camera and lens, and make sure the tripod can provide reliable stability and shock absorption. The latter three are exclusive to autofocus.

3. Take the most common camera focusing method—phase detection focusing of single-lens reflex cameras as a standard analysis. The reflector of the SLR body is composed of two pieces of reflective glass - the primary mirror and the auxiliary mirror. The central part of the primary mirror is transparent and corresponds to the auxiliary mirror. The primary mirror and the auxiliary mirror together project the lens imaging light to the frosted glass, and the auxiliary mirror will reflect part of the light to the bottom of the mirror chamber - the phase detection autofocus module. There are two small lenses in the module, each of which captures a small part of the image on both sides of the focus area, and then projects it onto a CCD array divided into two groups. Conceptually, these two small lenses are located behind the photosensitive chip, and they focus the captured images on the CCD array (see the figure below).

4. If the lens is accurately focused, the two refocused images will be in the center of their respective CCD arrays (black lines in the picture). The distance between the two (known in advance) is the phase when the focus is accurate. (phase). But if the imaging position of the lens is in front of the photosensitive chip (blue line in the picture), the distance between the images on the CCD is relatively close, that is, the phase is relatively short; conversely, if the imaging position of the lens is behind the photosensitive chip (red line in the picture), the CCD The distance between the two images above is relatively far, that is, the phase is relatively long. Therefore, by comparing the difference between the quasi-focus phase and the non-quasi-focus phase, we can calculate the movement direction and distance of the lens when focusing, and then issue movement instructions to the lens and place the lens in position at once, so that the focus is successful.