How Does Dual-Pixels CMOS Autofocus Canon

How Does Dual-Pixels CMOS Autofocus Canon

The Canon 70D is one of the last born in the house and Canon has a substantial innovation in the world of digital cameras by introducing the dual-Pixel CMOS autofocus. This system is nothing more than an evolution of autofocus contrast (follow the link to read related article) that allows you to make effective AF even when the mirror is raised, or when tracking a moving subject and, more importantly, when shooting video.

Recall that the focus for phase variation (typical SLR) is through the use of a sensor different from that of acquisition and that the light towards it arrives from the mirror, when it is in position “rest” (i.e. not shooting). But when the mirror is raised and then we are acquiring images (live view, for example), the AF phase change is no longer available and the camera uses the focus of research for contrast, much slower: the main sensor continues to compare the captured images until it identifies the image in focus, by acting on the engine of focus in order to vary the latter. The problems of these systems were two: the first was related to the speed of the processor that makes the comparison (now largely overcome the problem), the second was (and is) the inability to know “to focus” to get closer to correct result.

The camera, in fact, starting from the first frame, acts on the engine focus to the left or right “at random”. If the direction is wrong, the camera lost time unnecessarily. A waste of time is remarkable that in the videos become irritating because we will be a bit ‘of frames out of focus.
Nikon and Canon especially in recent years, have tried to remedy this problem by pixel for the autofocus function within the main sensor (the image capture). A solution that, in practice, would work also in the presence of mirror was raised. Unfortunately, the first experiments were not really positive mainly due to poor miniaturization of photodiodes: inserting a few pixels allocated to the AF sensor is rendered almost useless this system in the presence of lighting not quite full, but inserting too many are going to dramatically reduce the brightness scene.

With the dual-pixels CMOS autofocus, Canon has solved this problem in a radical way. Canon has in fact completely redesigned the photo sensor, doubling the number of photodiodes present on it and allotting half to the acquisition of the image and the other half to the AF. Hence the name dual-pixel is as if each photodiode sensor was divided in two.

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