Canon 6D lệch focus ở điều kiện ánh sáng trong nhà

[thaison_photo]

Cái này không phải back focus mà chính xác là không focus được vào chủ thể ta muốn vì AS yếu hay chủ thể thiếu tương phản.

Dạ đúng ạ, em ko có nói back focus mà bác, em nói lấy nét hụt, digic mấy thì cũng là máy móc cả thôi, hehe

[robogundam1945]

Dạ đúng ạ, em ko có nói back focus mà bác, em nói lấy nét hụt, digic mấy thì cũng là máy móc cả thôi, hehe

chà, tới giờ mới biết rõ hơn điều này, đổ tội oan cho con Sigma art, thanks bác nhé

[riosun269]

Nhưng trong điều ánh sáng yếu thì dùng focus live view vẫn chính xác hoàn toàn. Chỉ có focus view finder mới bị hụt thôi

[danca]

Các bác tham khảo
An AF system essentially consists of a sensor system that is linked (via the camera's processor) to the AF motor, which will either be in the lens or the camera body depending on the model.

There are 2 kinds of autofocus. Active AF uses methods such as ultrasonics or infrared to measure the distance between the camera and the subject. A pulse is emitted from the camera, bounces off the subject, and returns. The time this takes is calculated in-camera and used to determine the distance. This kind of AF is independent of the lens/mirror system of the camera.

Passive AF analyses the image in the viewfinder instead. 2 methods are used in Passive AF. The first is Phase Detection. Here the image is split into two in the camera and the different phases of the two images are analysed. It achieves range-finding by essentially comparing how the two images diverge on the sensor. This is the system most modern DSLRs use, as it is the most accurate.

The second passive AF system is Contrast Detection. This is most commonly used in video cameras, and in DSLRs when in live view mode (essentially the same as a video camera). It works by analysing the contrast between pixels; the better the image is in focus, the greater the difference in intensity between pixels. So the camera checks intensity, focuses a little, checks again, etc., until it achieves a focus that gives an acceptable (preprogrammed) intensity difference. There is no actual range-finding going on. Contrast Detection is generally slower and less accurate than Phase Detection.

As for accuracy, generally, if used correctly, AF systems are very accurate (Passive Phase Detection being the most accurate). However, they often have problems in low-light (hence the AF lamp that comes on when you try and focus in the dark). The user also has to make sure that they are focusing on the correct point (e.g. focusing on the subject not the background).

[robogundam1945]

tiện thể mình thấy Sigma có cập nhật Firmware cho Sigma 35 Art, tăng độ ổn định cho ống kính đó, bác nào thử update chưa? không biết mang ra Shiro có update cái này cho mình ko nhỉ

http://www.sigma-global.com/download...5_14_A012.html

[riosun269]

Mình có cả USB dock. Nếu có rảnh thì hú cafe mình up cho cái một :D
facebook mình: https://www.facebook.com/riosun1989

[robogundam1945]

Mình có cả USB dock. Nếu có rảnh thì hú cafe mình up cho cái một :D
facebook mình: https://www.facebook.com/riosun1989

đã send request cho bác nhé