I love my NEX but...

Started Nov 22, 2013 | Discussions thread
jpr2 Forum Pro • Posts: 15,554
re: while the DualPixel design in the 70d is a very, very neat idea...

captura wrote:

jpr2 wrote:

  • ...MATCH the speed of PDAF-classic in even middle-class DSLRs implementation anytime soon;
  • maybe with the release of A7 mk-II, or Nex-7 mk-III in the II-nd half of 2015 ??
  • supposedly the N7 mk-II we are going to see in mid Feb. 2014,
  • but I'd not count on any big strides for its OSPDAF;
  • it is not going to be any quicker than the OSPDAF of A7 (released Oct. 2013);
  • too soon for anything significantly better yet,


The one to watch now...

"The EOS 70D is a mid-range SLR for enthusiast photographers that from the outside looks like a sensible, indeed desirable upgrade to the EOS 60D. It borrows many of the best bits from Canon's existing SLRs, including the autofocus sensor from the EOS 7D, the fully articulated touchscreen from the EOS 700D (Rebel T5i), and built-in Wi-Fi from the EOS 6D. But on the inside it sports an entirely new sensor that is, potentially, revolutionary. It offers 20.2MP resolution, but uses a 'Dual Pixel CMOS AF' design in which every single pixel is split into two separately-readable photodiodes, facing left and right. This means that in principle they are all capable of phase detection autofocus in live view and movie mode."


...with a really lots of promise too (and perhaps it will be soon realized in the 70d mk-II, or some other body from Canon - e.g. in Eos-M mk-II, hopefully with a built-n VF this time), but right now it is not yet without some severe problems - you should have noticed them in the very same DPR's review.

"These tests are all very impressive, but Dual Pixel AF does have its problems, most notably to do with tracking a moving subject during continuous shooting. The 70D offers a 'Face Detect + Tracking' mode, in which it can follow your subject's face as they move around the frame, and keep them in focus. But if you combine this with continuous shooting - both high and low speed - the camera locks focus at the first frame, and doesn't attempt to refocus for successive shots. Worse still, the screen blacks out completely during continuous shooting, making the whole thing something of a guessing game, particularly when panning to follow a moving subject. This means that Dual Pixel AF is effectively limited to being a 'one shot' mode when shooting stills.

This behavior is disappointingly reminiscent of first generation mirrorless cameras, which worked in much the same way. It looks very dated compared to the most recent models, which offer continuous shooting modes that show live view between frames, and can refocus between shots. This requires them to shoot at a reduced rate compared to their fastest possible, but the Olympus OM-D E-M1's 6.5fps with focus tracking isn't exactly sluggish. Hopefully Canon will develop and improve future generations of Dual Pixel AF in much the same way.

Overall, our impressions of the Dual Pixel AF system are pretty positive - it's one of the fastest live view focus systems in a current DSLR, so there's not such a dramatic shift in behavior when you switch to live view shooting as with most DSLRs. We've also found that it offers clearly greater accuracy and consistency than the conventional AF system. It's worth noting that while you can use AF adjust to fine-tune the behavior of the conventional AF (and may well need this to get usable results), the setting has no effect on the live view autofocus.

It's also worth noting that the Dual Pixel AF system doesn't necessarily use the same aperture as will be used to take a photo - instead it will use the diaphragm to control the amount of light reaching the sensor. In our tests, we found that this could result in a very small drop in consistency, if you're shooting images with a wide aperture in bright light, because that's where you'll have the largest discrepancy between the camera's working aperture value and your chosen shooting aperture.

Overall, any inaccuracy we have found with Dual Pixel AF has been very small. Anyone sticking with the kit lens will likely never encounter the difference we found between conventional phase-detect and Dual Pixel autofocus, but those with larger lens collections or who plan to purchase faster zooms and primes will benefit from shooting in live view mode with the 70D. Far from being 'just for video,' Canon's Dual Pixel autofocus does seem to offer a good balance between speed and accuracy, making it a good go-to mode when sharpness is critical, espeically when shooting at large apertures.

Overall, our testing makes it appear the 70D's Dual Pixel AF gives most of the speed advantage of conventional phase detection AF and most of the accuracy benefits of contrast detection, but doesn't quite manage to offer all of both.

Sadly Dual Pixel AF is only really used for single image AF or movie shooting (see the movie page to see how it does). If you need continuous autofocus with tracking, you have to use the 70D's conventional AF system".


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