Canon EOS 70D Digital Camera Review
Canon's flagship APS-C camera finally delivers on the video DSLR promise—with a catch.
The Canon 70D has still got it where it counts.
In our labs, the Canon EOS 70D proved that it can still hang with the competition. The 70D excelled in our color accuracy and white balance tests, though it was merely average in our noise, dynamic range, and sharpness tests. Fears that the 70D's unique Dual Pixel CMOS structure would negatively impact image quality seem unfounded, when looking at our results. The 70D lags behind the competition from Sony, Nikon, and Pentax for dynamic range and high ISO performance, but this has been the case across Canon's product lineup recently, so it hardly seems like Dual Pixel AF is the villain here.
The 70D is also much snappier in general operation than we remember with the 60D, capable of a respectable 7.06 frames per second by our measurement, thanks to Canon's new Digic 5+ processor. That speed—not to mention the improved 19-point, all cross-type AF sensor—actually puts the 70D right alongside Canon's other high-end APS-C camera, the 8fps-capable EOS 7D. Announced in 2009, the 7D is ostensibly's Canon's leading APS-C camera, but it's by far the oldest model in Canon's stable, preceding even the 60D. With the 70D also coming in at around $300 cheaper (body-only), there simply aren't many reasons to opt for the aging 7D, with rumors of an update swirling for more than a year.
Of course, one of the main reasons to opt for the 70D is the superb video performance. The 70D offers full PASM exposure control, smooth 1080/30p recording, and the option of either IPB or ALL-I compression, similar to the Canon 5D Mark III. ALL-I has a slightly higher bitrate, compressing each frame individually; it takes up more space than IPB with only a marginal quality improvement, but it's easier to edit. For example, in our bright light motion testing, a 40 second ALL-I video shot at 1080/30p took up about 450MB, while a comparable 30-second IPB clip was just 110MB.
In our video tests we found the 70D's video to be sharp, smooth, and free of most kinds of artifacting. The 70D was also a strong performer in low light, requiring just 2 lux of light to produce a 50IRE image on a waveform monitor. Focus in video and live view was also excellent, thanks to the Dual Pixel AF technology. (Segue!)
Dual Pixel CMOS AF
Kind of a big deal
Without question, the real star of the show for the 70D is the new Dual Pixel autofocus, which turns the entire image sensor into one big phase-detect AF unit. As a primer, phase-detect AF works by taking the incoming image and splitting it, creating a parallax effect similar to how 3D glasses work. (You get a similar effect by closing one eye and then the other.) By sensing how different the two versions of the image are, the camera can figure out exactly how out of focus the subject is. Using that information, the camera can predict where the subject is and, more impressively, where it will be when the lens can catch up.
Most DSLRs—including the Canon 70D—primarily achieve PDAF when shooting still images by reflecting a small portion of the incoming light to a smaller, dedicated AF sensor. The issue there is that when you want to do things like engage live view or record video, you have to flip the DSLR's main mirror upwards, cutting the AF sensor off from precious light. This forces most cameras to rely on slower contrast-detect autofocus, which simply moves the lens in one direction until contrast (and thus focus) peaks and begins to fall, backtracking to the correct point.
Dual Pixel AF solves that issue at the silicon level, as Canon has designed every pixel to work for both focus and image capture. Millions of microlenses placed over the sensor gather light from all angles, with each lens splitting the incoming image over two pixels—hence the name Dual Pixel AF—with the camera computing the phase difference. It does this across the entire sensor, essentially creating a multi-million point phase-detect autofocus sensor. The result is silky-smooth AF that is accurate, can track motion, and can simply tell the lens where it needs to go or where the subject will likely be.
In short, Dual Pixel AF is a massive upgrade over previous DSLR video efforts. In the DSLR video revolution, this is the storming of the Bastille. Even cameras that offer integrated phase-detect on sensors aren't this smooth, as they only draw from maybe 100 points at most. For the 70D, having the entire sensor feeding autofocus information results in simple, accurate AF with none of the hitches that have tripped up previous DSLRs. Canon is clearly proud of the accomplishment, as they should be. The only thing that remains to be seen if Dual Pixel AF will make its way to Canon's entry-level Rebel line, where it will do the most good. Since Canon fabricates all of its own image sensors, it seems like a safe bet that Canon will re-use this particular image technology in everything going forward. We hope so, since it's clearly the biggest advancement in DSLR video we've seen since the D90.
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