The imaging sensor jumps to 20.2MP from 18MP, and sensitivity adds a stop, now topping out at an equivalent of ISO 25,600 when ISO expansion is on. Continuous drive mode now allows for 7fps burst shooting, up from 5.3fps. Canon hasn't yet announced how many shots you can expect per burst, though they never do so until a camera goes into full mass production. The AF system gets a big boost from the 60D's 9-point system, to the 70D's 19-point all cross-type system, with the center being a dual-cross high-precision point when used with f/2.8 or faster lenses.
It's the same AF system used in Canon's flagship APS-C DSLR, the EOS 7D. The LCD remains at 3-inches and 1,040,000-dots on a fully articulated hinge that lets it flip to the left side and angle up or down, but is now a touch screen. Built-in Wi-Fi offers the same functionality we loved in the EOS 6D. Video capture includes the full suite of H.264 recording found in all of Canon's flagship EOS 1D X and allows capture at up to 1080p 30 frames per second and a choice between ALL-I or IPB codecs. One thing it is lacking, however, is a headphone jack, something video shooters often crave.
Canon has doubled the number of photodiodes on the sensor, pairing them up in each pixel so that they can perform phase detection autofocus from each pixel site, though the 70D uses an area covering the center 80% of the width and height of the frame.
Traditional phase detection AF works by diverting some of the incoming light from the lens to a secondary sensor in which pairs of sensors compare the phase of the light arriving at the sensors. Once it sees what the difference in phase is, the camera knows how far it needs to move the focusing elements in the lens, tells the lens to move to the necessary location and focus is achieved. Canon's new Dual Pixel CMOS AF works the same way, except it does so without diverting the light to a separate sensor. Instead, the imaging sensor uses the paired photodiodes separately for AF and then together when capturing an image.
While the new AF system can function with lenses that have maximum apertures as slow as f/11, faster lenses should have tighter tolerances for focusing with Dual Pixel CMOS AF since the lens isn't stopped down until the image is captured and the shallower depth of field that faster lenses provide creates a tighter area within which the sensor can find focus.
The 70D does include AF micro adjustments for use with the traditional AF system. Also, unlike the Hybrid AF system found in the T5i and the Hybrid AF II found in the SL1, the Dual Pixel CMOS AF is just as fast with one of Canon's EF or EF-S lenses as it is with an STM lens, though the STM lens should provide less noise and vibration to the camera's built-in microphone. Of course, AF speed typically varies from lens to lens due to the size and weight of the focusing group and differing motor configurations, so you can still expect some variation in focusing speed, though they likely won't be drastic.
Because of the new system, focusing during Live View is now handled entirely by the phase detection system. Previous cameras like the T5i and the SL1 use phase detection for most of the focusing, but rely on contrast-based AF to lock-on. The result is a jitter just before focus is achieved. It's not a huge deal with still photography, but for video, it can be distracting. On the whole, AF during video mode has improved substantially. We only had a few minutes with a pre-production unit, but it really does focus the way you'd expect a dedicated camcorder to.
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