Compared with the EOS Rebel SL1, which employs Hybrid CMOS AF II, the EOS 70D Digital SLR camera (scheduled to go on sale in September 2013), which is the first camera to feature Dual Pixel CMOS AF, not only achieves AF speed that is approximately 30% faster but also delivers improved Movie Servo AF tracking for continuously smooth focusing during video shooting, even when filming quickly moving subjects.
Here is the description of how it works form the Cannon's technology page:
"Each pixel on the EOS 70D camera's sensor consists of two independent photodiodes that function both as imaging points and as individual phase-difference AF sensors. When the shutter button is pressed, parallax images on each photodiode of the pixel are detected, the amount of lens drive is calculated to correct the amount of shift in the AF points, and AF is achieved nearly instantaneously. During image capture, the same two photodiodes record the image and output as a single pixel. By placing approximately 40.3 million photodiodes on the camera's sensor, two per pixel, this caliber of AF is possible on approximately 80% of the image plane, vertically and horizontally. When the image or video clip is being captured, the CMOS sensor behaves as it always has with EOS SLR cameras, unimpeded by the dual photodiodes and recording each individual pixel with virtually no loss of detail or sharpness."
Update: Canon Singapore published Vimeo video on the Dual Pixel AF principle:
Reading about Lytro and the ToF book today...
ReplyDeleteThe phase-detect side of this 70D sensor should provide a very high resolution set of data about depth in the image, right?
Would it be possible to construct a depth image using this? What resolution would it have? And how accurate would that depth info be? (I know it's pretty accurate around the focusing distance, but is it still so when closer or farther?)
Samuel H
It's only very slightly similar.
ReplyDelete70D sensor produces 2 images, from the left and right halves of the lens aperture. One microlens on the sensor per 2 half-pixels.
Lytro divides the lens aperture into about 100 sub-apertures, giving 100 images - that's why it has about 1/10th of the resolution. One microlens near the sensor per 400,000 pixels ?
Eric D
Of course, the story from Canon is probably very much over-simplified. If all pixels were split into left|right, it could only focus on vertical lines ! Half the pixels must be split into top|bottom to focus on horizontal lines, so there are 4 images. At least ...
ReplyDeleteI think it is just simplified model, the real pixel array pattern should consider the right-left and up-down dirextion.
Deleteleft-right, top-down? You are kidding right?
ReplyDeleteIf the object is in focus, it is focus for both left-right and top-bot.
And if the object is in back or front of the focus, it is not in focus for both checks.
Yep, if you have pure gradient. Or image full with horizontal lines, you will not be able to focus... But who shoot pictures of exactly the same horizontal lines? (And you still need to absolutely 0 tilt on your camera and 0 barrel distortion) to come to such limitation of the focusing system.