Phase, Contrast, & Hybrid Autofocus... What's the Difference?


Mirrorless cameras have more advantages than just a compact size over DSLRs. If you were going to take advantage of a camera's phase detection autofocus or even hybrid focus system you can't use them in most DSLRs in photo mode. You can only take advantage of the system in live mode or when shooting video. Gerald Undone has done an essential masterclass on modern autofocus systems. and it's worth watching. 


So, what's the difference between all the focusing systems? Here's a brief rundown. 


PHASE DETECTION

Phase-Detection.png
(phase detection image from Wikipedia)

Phase detection is quite complicated. It basically takes light coming into the lens and bounces it off two or more small image detection points (aka, the points listed when it says a camera has X number of Phase detection AF points).

If an object is in focus then the light rays from the extreme sides of the lens converge in the dead center of each point. If it's out of focus then the light would be on different sides of the point. Having these data points make it easier for the camera to know how far out of focus the images is and what direction.  

This makes focusing extremely fast and accurate as it's comparing images and points from multiple spots making it more accurate for fast-moving images, sports or wildlife photography. 



CONTRAST DETECTION

CONTRAST DETECTION.pngContrast detection, in a nutshell, slides the lens back and forth until the object is in focus or until the camera determines the image has the best contrast. 

The disadvantage is it doesn't know how far out of focus an image is or what direction the lens needs to move to get there. That's why in low light sometimes you're lens with shuffle back and forth trying to get a clear image. 

It will keep sliding the lens until the image is in focus and then overshoot and back up a bit just to make sure it's in focus. This makes the contrast AF more accurate than phase detection, but considerably slower. 


HYBRID AUTOFOCUS

Hybrid autofocus incorporates both contrast and phase detection systems. It starts with a phase detection system and then fine-tunes the image with contrast detection. 

However, on modern mirrorless cameras, part of the sensor's pixels are taken over by the phase detection pixels which in regards to DSLRs you couldn't use in photo mode and only in live mode. 


DUAL PIXEL

Canon created their legendary Dual Pixel autofocus, which included phase detection on nearly every pixels the camera's sensor. This gave you the data range of contrast detection but at the speed of phase detection. It too has its limitations. It's not quite as accurate as a contrast detection system and it's not as fast as modern hybrid systems. The new Canon EOS R allows you to use dual pixel all the time though and not just in live mode, which makes it a better system than it used to be. 

In summation, today's camera's have faster and faster processors enabling quicker computations of focusing data, so, once you get to the flagship models of each manufacturer, they all work, and they all work pretty great. It's going to come down to what your needs are? Are you shooting more video than stills? Then perhaps a dual pixel autofocus is for you. Are you shooting more action, then maybe a hybrid or phase detection system. Are you shooting portraits... Then it doesn't really matter.  

Please check out Gerald's full video at the top for a truly astounding and easy to understand video on all the modern focusing methods our fancy cameras used to keep our life in focus.