How does iPhone 6 autofocus compare to DSLR autofocus points?

Asked 3/20/2016

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DSLRs often advertise a specific number of autofocus points, but the iPhone 6 is described in terms of "Focus Pixels" instead. How many autofocus points does the iPhone 6 have, and is that number directly comparable to the AF point count on a DSLR?

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

10y ago

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You are wanting to compare apples to oranges.

DSLRs us a separate autofocus sensor to do Phase Detection Auto Focus so that the mirror can remain down and the scene can remain visible in the viewfinder during focusing. PDAF uses light from opposite edges of the lens to measure the distance to the subject using the same principles as stereoscopic rangefinders. A PDAF sensor actually employs dozens if not hundreds of pixels per each focus "point".

Camera phones such as the iPhone 6 use the actual image sensor to do focusing, traditionally using Contrast Detection Auto Focus. CDAF measures contrast in the scene and moves the lens until the amount of contrast is maximized in the area. Traditional CDAF has generally been more accurate than PDAF, but at the expense of being much slower.

Recently, hybrid sensor based AF systems have been introduced that modify some of the image sensors pixels to be more sensitive to light from one side of the lens or the other to mimic the capability of a PDAF array. This reduces the overall efficiency of the pixels so used, but they are usually a very small percentage of the sensor's total pixels. These modified pixels are used to get the focus very close much more quickly than CDAF could in the past, then CDAF is used to fine tune the focus. How many "focus pixels" a camera's image sensor has can't be equated to the number of focus points a PDAF system has, because it takes many "focus pixels" on the CMOS sensor to do the same thing as the many pixels that contribute to each PDAF focus point.

Originally by user15871. Source · Licensed CC BY-SA 4.0

user15871

10y ago

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AI Answer

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Not in a directly comparable way. DSLR autofocus “points” and the iPhone 6’s “Focus Pixels” are different technologies.

In a DSLR, autofocus points usually refer to dedicated phase-detection sensors used while viewing through the optical viewfinder. Each AF point is not just one pixel; it uses multiple sensing elements.

The iPhone 6 focuses using the image sensor itself. Traditionally phones used contrast-detect AF, and the iPhone 6 also includes on-sensor phase-detection elements marketed as Focus Pixels. One answer cites chip analysis showing roughly 50,000 phase-detection pixels on the iPhone 6 sensor.

However, those are individual sensor pixels, not DSLR-style AF points, so comparing “50,000” to a DSLR’s AF point count would be misleading. They serve different roles and are measured differently.

So the best answer is: the iPhone 6 has on-sensor phase-detection pixels, reportedly around 50,000, but it does not have a DSLR-style AF point count that meaningfully matches what camera makers advertise for interchangeable-lens cameras.

UniqueBot

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10y ago

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