Bigger smartphone apertures don’t count if the sensors get smaller

In the past few years, smartphone manufacturers have started paying more attention to the optics they use on their smartphone, using wider apertures for better low light performance. That’s awesome, but as a photographer, I have an ongoing gripe about the marketing buzz around apertures: An aperture tells you little about performance if you don’t know the camera’s sensor size.

As a refresher, all else being equal, wider apertures (a lower number) mean better low light performance and shallower depth of field (more background blur or ‘bokeh’). The problem with smartphone photography is that rarely is everything else equal, sensor size in particular.

I’m going to oversimplify things a bit, but let’s assume two phones are technologically identical except for their aperture or sensor size. If two phones have the same sensor size, the one with the wider aperture will be better. But by the same token, if two phones have the same aperture, the one with the larger sensor will win.

If both of the variables are different, well, things can get pretty messy.

To use an exaggerated example, here’s a photo taken at F1.8 on the Pixel 2.

And here’s a photo taken at F3.5 on a high-end camera with a much larger micro-four thirds sensor.

Despite the ‘wider’ aperture on the Pixel, the micro four-thirds camera has much more blur (and would theoretically perform much better in low light too). That’s because the micro four thirds sensor is capturing more light overall thanks the much larger surface area on the CMOS chip.

To drive the point home, here’s the micro four-thirds camera at F1.8

This image compares common sensor sizes for different camera categories. The Pixel 2’s sensor is believed to be 1/2.55,” or a teensy bit smaller than the smallest sensor on that image. You can see the dramatic size difference.