Image Quality and Performance

The iPhone 5s is very fast in general use, with most apps opening nearly instantly. iOS 7’s elaborate animations are flawlessly smooth. 

That pep carries over to the camera app, which opens in a flash, around half a second. Any waiting you experience will have more to do with focus time than any start-up lag. There’s essentially no shutter lag, nor will you notice any shot-to-shot waiting: the 5s will bang out frames as fast as you can poke the button (you can manage 6 or 7 frames per second with a quick finger). If that’s not enough, there’s always the nearly bottomless 10 fps burst function. Even HDR shooting doesn’t slow things down much, and there’s no waiting for the phone to digest a long burst either.

Apple's A7 processor provides plenty of power to ensure smooth operation, fast shot-to-shot times and no waiting after shooting a burst.

Focus feels quick but not dramatically so. The vagueness of the focus lock confirmation detracts from the sense of responsiveness that the underlying speed of the AF process might otherwise provide (though you can lock focus with a long press on the screen). Focus accuracy is reliable in normal light, but falls off a bit in very low light conditions.

Daylight, Low ISO

In good light the iPhone 5s captures high quality images with solid detail for an 8-megapixel sensor. The results are typically satisfying for anything from reasonably sized prints to web sharing. 

Colors are richly saturated but stop short of going over the top, with results that “pop” but don’t look gaudy. If you want more muted colors, you’ll have to handle it in post as there’s no way to tweak color (or virtually any other parameter) at capture time.

The phone’s auto exposure algorithm is rarely fooled into making serious mistakes. It deals with challenges like high contrast scenes well. The 5s doesn’t work any miracles in the dynamic range department, but neither do any of its competitors: that’s what the HDR mode is for.

At 100 percent screen views (aka pixel peeping) the 5s’ output holds up pretty well for a phone: Apple’s conservative approach to noise reduction at low ISOs pays off with a lot of pixel-level detail that’s useful if you need to heavily crop an image. The flip side of that is that even at base ISO a fair amount of noise crops up in moderately dark areas of even tone (like deep blue skies) and darker parts of otherwise-bright scenes. This is par for the course in cameras that don’t deploy aggressive noise reduction.

The 5s’ lens is very sharp, not just in the center of the frame, but also in the corners where some of the competition falls down. Other factors can eat into details (noise, camera shake) but you don’t have to worry about the lens.  

In good light the 5s captures solid detail and rich colors with very good corner-to-corner sharpness.
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The 5s does a good job of holding detail in darker, low contrast areas.
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Light-handed noise reduction helps preserve details, but luminance noise does creep into even tones like skies and shadow areas of the image.
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The 5s has trouble holding detail in both highlights and shadows in a scene with a wide brightness range, but it’s no worse than its competition.
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White balance in sunlight is accurate, with nicely rendered skin tones.
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More impressively, the 5s manages pleasing colors in this coolly-lit shade scene, a situation that many phones will render with a bluish cast (though in mixed shade and sun, the shady parts of the scene do turn out cooler).
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Low Light, High ISO

The 5s’ low light performance is good, though it’s at most a subtle improvement on what the iPhone 5 delivers. In terms of straight “image quality at ISO X” terms, this still puts it among the best, excluding the outlier of the Nokia Lumia 1020. 

However, the 5s can’t stoop to the slowest shutter speeds available to phones with optical image stabilization, which means lower image quality in certain situations. The 5s does do some neat digital tricks to improve the odds of sharp shots at its minimum shutter speed of 1/15 sec (see Image Stabilization in the Camera Features section of this review for more details).

The 5s’ F2.2 lens is within a negligible quarter stop of the fastest phone lenses on the market, so it gets about as much light on the sensor as anything out there. With the aperture fixed, when light levels drop it’s a matter of lengthening shutter speeds and raising sensitivity (ISO) to get a usable exposure. 

The 5s’ base ISO is 32 (though for some reason it occasionally uses 40 in very bright scenes), and it maxes out at 2500. Unlike the iPhone 5, the 5s doesn’t appear to perform pixel binning at high ISOs, meaning there’s no sudden drop in resolution when that kicks in. Detail begins to erode above ISO 125 but even at ISO 320, images are good for just about any use. From there it’s a gradual decline in detail until things really hit the wall at ISO 2000 and above, when saturation drops noticeably and detail is severely compromised. That said, even ISO 2500 can produce images that look good at web resolutions.

This ISO 125 shot is two stops above the 5s’ base sensitivity, but noise isn’t a problem and there’s plenty of low-contrast detail to be seen.
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By ISO 320, pixel level detail is taking a pretty serious hit, but as long as you don’t zoom in too much the image looks good.
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The 5s picks ISO 640 for this night scene, and wisely avoids overexposing the central action. At screen and web resolutions this image works well, but a lot of detail is being sacrificed to keep noise under control (but it is under control).
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Luminance noise is visible at screen resolutions in this ISO 800 image, and there’s chroma blotching just beginning to rear its ugly head. Detail is hurting. This will still hold up very well at web resolutions.
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This dark city scene pushes the ISO to 1250. Luminance noise is plainly visible at screen resolutions, but overall the image doesn’t look too bad. This still looks good at web resolutions.
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It has to be pretty dark to hit the 5s’ ISO ceiling of 2500. Luminance noise and noise reduction have obliterated anything resembling fine detail here, and there’s chroma noise that’s visible even at web resolutions. That said, this photo is still perfectly usable for casual social media sharing.
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If the 5s’ lens has a weakness, it’s flare, the occasional distracting artifact caused by light reflecting within the lens. There was an internet kerfuffle about the iPhone 5’s tendency to produce purple flare with bright light sources just outside the frame. We observed a bit of this with the 5s as well, but wouldn’t consider it a major issue. Most phone cameras will flare under the right (that is to say, wrong) conditions. That said, we did notice more specular flare (bright dots) than we normally see in our night-time city shots. The 5s seems a bit more flare-prone than most phones, but it’s not a deal-breaking flaw.

This shot shows both purple flare from a light in the top right corner and specular flare in the form of orange dots in the sky. Purple flare can usually be avoided by a small adjustment of the camera position: specular flare is harder to work around, but less intrusive.

Flash

According to Apple, the 5s’ two LEDs (one white, one amber) match the color of the flash to the color of the ambient light in the scene, producing more natural-looking photos. Comparing the output of the 5 to 5s largely bears out this claim, as seen below.

This iPhone 5 shot is fine by LED flash standards, but the skin tones look a little greenish-yellow.
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The 5s’ flash does a better job creating more natural skin tones under artificial light.
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We observed some serious overexposure in close portraits with flash. Backing up a little helped.

The fact that the iPhone 5 used the same shutter speed but an ISO setting two stops higher suggests the 5s’ dual LEDs kick out more total light than the 5’s single LED flash. However, the 5s still can’t hold a candle (ha) to the more powerful xenon flashes that Nokia has put in its Lumia 1020 and 928 handsets. The relatively long pulse of light (and hence, slow shutter speed) that LED flash requires can also result in blur from subject movement, as seen in the 5s example above if you zoom in.

In auto flash mode, the 5s tends to crank up ISO (to 2000 and even 2500) before resorting to triggering the flash. In some of these situations, you’re better off forcing the flash on manually.