Canon EOS 70D video AF test: how well does the new sensor-based AF perform

By Kevin Carter - Tuesday, September 17, 2013

Camera Article
Introduction | Autofocus for video | Canon EOS 70D VS Sony SLT A77: Video Comparison | Canon EOS 70D VS Sony SLT A77: Shooting Time Lag | Conclusion | Videos around the web

Canon EOS 70D vs Sony SLT A77: test protocol

01-canon-70d-af-test

Canon EOS 70D and Sony SLT-A77 side by side in the labs

To perform our tests, we mounted the two cameras side-by-side on a Manfrotto 405 Geared Head and studio stand. For an impartial test, we used the Canon EF 40mm f/2.8 STM (at full aperture) and the Sony DT 16-50mm f/2.8 OSS SSM, set at 40mm f/2.8. The f/2.8 maximum aperture was used on both models, as full-time AF is only available in Program P mode on the Sony where it’s restricted to using apertures down to f/3.5 only.

Clips were recorded simultaneously with the cameras set to record to the same video specification (1080/25p). Resultant excerpts are displayed spliced side-by-side (on the left is the Canon EOS 70D, on the right the Sony SLT-A77) for direct comparison.

02-canon-70d-af-test

In this behind the scenes view, we’re evaluating autofocus stability under variable lighting conditions.

Autofocus accuracy on fast appearance

Bright light conditions

Under bright lighting, the two rival systems perform very well indeed, with the majority of focus changes being both reasonably fast and accurate. With nearly 20 focus distance changes, the Canon focused accurately each time.

The Sony only made one mistake (close distance, at around 56 seconds), yet it’s quite obvious the Sony AF system is faster. That’s not as bad for the Canon as you might think. In cinematography, outright speed is outweighed by smoother focus (providing focus speed is fast enough to keep the subject in focus), which the Canon revealed.



Low light conditions (tungsten 20 Lux)

When tested under lowlight conditions (20 lux, roughly the equivalent to shooting at dusk), the Sony SLT-A77 performed nearly as well as the Canon, despite only 30% of the light entering the mirror-box being used for AF in the Sony.

Needless to say, under these tough conditions both models performed admirably well.



Autofocus accuracy for tracking

Bright light conditions

In this video clip the two systems perform well again. Needless to say, the Canon EOS 70D is slightly slower as we’ve seen before, while the Sony SLT A77 reacts quickly but displays lens breathing (a change of angle of view during shifting of focus).

Even if the EOS 70D is slightly slower compared to the Sony, the Canon’s system is never really out of focus.



Low light conditions (tungsten 20 Lux)

Under the same low light levels as before (20 Lux), the Canon EOS 70D is clearly the better at focusing of the two on test.

Disregarding the better color and exposure accuracy of the Sony SLT-A77, the camera’s focus system struggles to track the subject in low light and loses focus on several occasions.