Here are two inscrutable numbers: f/2.2 and f/1.7.
The first represents the iPhone 6s Plus camera's aperture. The second is the Galaxy S7's. A difference of 0.5 gives the Galaxy S7 all the advantage it needs to blow the iPhone out of the water.
Here's what it means, and why it's so important.
Aperture is a measure of how wide a portal a lens opens to allow light onto the sensor. The wider it opens, the more light hits the camera's sensor, and the more light hits the sensor, the better the camera performs in low light. A low f-stop means a wider aperture than a high f-stop, which is why the Galaxy S7's f/1.7 is better than the iPhone's f/2.2.
A difference of 0.5 might sound small, but it's huge. Check out these images taken on an iPhone 6s Plus and a Galaxy S7:
You'd think a whole new bank of streetlights got turned on for the Samsung shot. But I took it just moments after the iPhone's. The S7 software tends to brighten images a little more than the iPhone's, but the aperture is doing most of the heavy lifting. And it's an astonishing difference.
Samsung isn't the first company to stick a super-wide-aperture camera on its premium smartphone, but it's the first to do it well.
The LG V10 and LG G4 shipped with f/1.8 lenses, nearly as wide-ope as the S7's. LG marketed the devices as smartphones for serious photographers. But when I took the V10 for a spin it disappointed:
The V10 is reasonably good in low light and shoots crazy sharp over long distances. But LG allowed a fatal flaw of wide-aperture lenses to creep into the device: vignetting.
Due to some complex physics problems we won't explore here, wide-aperture lenses tend to make images that are shadowy around the edges. I don't mind the effect in small doses, and some photographers love it. But the V10's went way too far. My shots came out looking like I'd made them on a pinhole camera, or passed them through a tacky Instagram filter. Whether through feats of engineering or software correction (and probably a bit of both), Samsung's managed to avoid vignetting entirely on the Galaxy S7.
The final advantage of wide aperture is an optical effect known as "bokeh."
Take a look at these pictures:
See how the same bottle cap is in focus in both shots, but the backgrounds look way different? On a wide-aperture camera, everything not in focus appears way more out of focus. That out-of-focusness is called bokeh. And you can see how much more bokeh shows up in the Galaxy S7's shot than the iPhone's.
Shoot a jet of water through a long, narrow opening — say, a hole drilled in a dam — and all the molecules should move in a fairly straight line after coming out the other side. In the iPhone, all the photons end up pretty much in order after zipping through a longer, narrower aperture. So even those not focused by the lens end up somewhere close to where they "should" be.
But take some dynamite and bust that dam open and the water is going to crash all over the place. There are just more routes for water molecules to pass through an opening that broad. The same thing happens with photons in the Galaxy S7. Except for a narrow focused band, the photons scatter creating a blur.
Don't worry about it messing up mis-focused pictures though. The phone is so small that bokeh only shows up on super-close up shots.
Also, one risk of wide-aperture lenses is that they loose control of that photon torrent and create ugly, angular, distracting bokeh. But the S7's has a nice, soft look that you don't see on cheap wide-aperture lenses.