Smartphone cameras have improved by leaps and bounds over the years, to the point where many folks are forgoing low-end compact digital cameras and using their phone as their main digital camera. Two of the most talked-about phones, the Apple iPhone 5s and Nokia Lumia 1020, take very different approaches to the camera design. The Lumia 1020 packs a marketing-friendly 41-megapixel image sensor that's physically larger than those found in typical compact cameras. The iPhone 5s uses an 8-megapixel image sensor that's larger than those found in most phones, but a bit smaller in terms of surface area when compared to a good compact camera like the Canon PowerShot Elph 330 HS.
Nokia's approach has some advantages, notably in digital zoom. And all those megapixels? The actual full-resolution images are closer to 38 megapixels, but most shooters will opt to use the downsized 5-megapixel photos the camera saves by default. That's more than enough resolution for sharing on the Web, though if you're a frequent printer it's not a bad idea to save the full-sized photos as well—you can always offload them to your computer if you run low on space.
Alas, neither camera is perfect. We've compared each one in a few key categories to help you decide which one is the best always-on-you camera to carry.
Sharpness
We look at two factors when evaluating image quality—sharpness and performance at the higher ISOs that are required to get a sharp shot in low light. Both cameras use a lens that covers a 28mm (35mm equivalent) field of view, and both feature a fixed f/2.2 aperture—that's on par with a decent prime lens in terms of light-gathering capability.
Despite its lower resolution, the iPhone 5s is actually sharper when you take the entire image into account. Imatest tells us that it scores 2,033 lines per picture height using a center-weighted score; we require 1,800 lines to call a photo sharp. What impressed us is its edge sharpness; that clocks in at 1,654 lines. That's not tack sharp, but it's perfectly fine for the Web, and it won't detract too much from prints. Note that the iPhone 5s resolution test was performed at ISO 200; there's no way to manually adjust the ISO to its lowest setting (ISO 32).
At 38 megapixels the Nokia 1020 scores 2,218 lines using the center weighted test, but the corners are noticeably blurry thanks to a poor showing of 692 lines. It holds up a bit better at 5-megapixels; the average score across the frame is 2,121 lines, and but the edges lag behind at 899 lines. The downsampling technology is working, improving the effective sharpness by reducing the pixel count, but if you're shooting wide-angle images, the corners are going to look better on an iPhone 5s shot.
Where the Nokia trumps Apple is in the digital zoom capability. The center sharpness of the 1020's lens is really good—3,068 lines at the full resolution. When you start to zoom and cut off those soft corners, you're left with photos that are impressively sharp from edge to edge. Of course, you can't zoom with the iPhone 5s; the trick to getting closer to you subject is just that—you need to physically move closer to your subject.
Left: Nokia Lumia 1020. Right: Apple iPhone 5s
Low Light
The iPhone 5s doesn't allow for manual control over ISO, and as such it's not possible to properly light our ColorChecker test chart and crank up the sensitivity to see just how well the camera does at the higher ISO settings it will default to in dim lighting. We do know that it's a backside-illuminated (BSI) CMOS design with a base ISO of 32. The sensor is of the 1/3.2-inch class; it measures 4.5 by 3.4mm. It shows very little image noise there, only 0.6 percent. We were able to evenly light our chart and back up our studio lights to the point where the 5s defaulted to ISO 400; that's a setting that is appropriate for moderately-lit interiors. It scored a very respectable 0.8 percent on our noise test at that setting. We consider a photo to be a bit too noisy when it crosses the 1.5-percent threshold. Image detail does suffer at ISO 400; which indicates that there's some noise reduction going on behind the scenes.
The 1020's image sensor is bigger; it's a 2/3-inch design, which measures 8.8 by 6.6mm. That's 3.8 times the surface area as the iPhone 5s, but the sensor packs in close to 5 times as many pixels. It shows a bit more noise than the 5s; about 1.8 percent at ISO 400. But the 1020 shows better detail at that setting, and images at ISO 800 are also quite impressive. By the time you hit ISO 1600 details start to noticeably smudge. Despite the iPhone's low scores, we're going to give the edge to the 1020 based on side-by-side comparison of ISO 400 samples on our calibrated NEC MultiSync PA271W display.