Dual Pixel Raw
What does Canon Dual Pixel Raw do, and do you need it?
Each of the EOS 5D Mk IV’S 30 million pixels is made up of two photo diodes that can be used together or individually. With Dual Pixel Raw, the data from each photo diode is stored, giving a pair of images shot from slightly different viewpoints. Storing two sets of information doubles the Raw file in size to 60-70MB and slows the maximum frame rate to 5fps.
Canon’s Digital Photo Professional (DPP) software allows photographers to perform one of three unique adjustments to Dual Pixel Raw files: Image Microadjustment, Bokeh Shift and Ghosting Reduction.
Image Microadjustment moves the point of peak sharpness slightly in front or behind the point of focus. In practice, this is more about shifting from the end of the eyelash to the eyeball than from the tip of the nose to the eye. Wildlife photographers might find that the eye of the subject can be sharpened up when they have not got exact focus, though there is a limited range of adjustment. Bokeh Shift makes use of the slightly different viewpoints of the two photo diodes to shift the viewpoint – and hence the out-of-focus blurred elements – in front of and behind the subject that’s sharply in focus. Potentially you can save an image of a bride that has her eye obscured by a bit of confetti. Finally, Ghosting Reduction is claimed to reduce the effects of lens flare.
Once the files are open in DPP, start the Dual Pixel Raw Optimizer from the Tools menu. You need to choose one of the three optimizations then adjust the amount of optimization. The best way to see the effect is to create multiple versions of the Raw file with different optimization, then switch between each one to see the change. Bokeh Shift and Ghosting Reduction can be applied to a specific part of the frame, if needed.
You’ll see the most obvious effects with fast primes in the 50-200mm range used wide open. Wide-angle lenses have too much depth of field and super-telephotos focused on distant subjects capture very little difference between the two viewpoints. Those who take portraits in natural light with wide-aperture prime lenses will see the most benefit from Dual Pixel Raw.