Performance and Image Quality:

Despite its name, the iPhone 5 is the sixth iPhone, and in the five or so years since the original model has launched Apple has had ample opportunity to polish things up pretty nicely. As such, the iPhone 5 doesn't really present any nasty surprises as regards its performance. Running iOS6, the iPhone 5 operates very quickly, very reliably, and in favorable conditions it is capable of great results. 

The touch-to-focus interface is all-but-ubiquitous these days, and very intuitive. Autofocus acquisition is nice and quick in daylight, and not bad in low light either. In most situations, under a mixture of lightting, AF is completely accurate. Face Detection works well when there are faces in the scene, but we've found that it has a tendency to detect faces that aren't there. Architectural details, the wheels of cars, clock faces... normally this isn't a big issue (sometimes it's hilarious) but if you're getting consistently odd exposures of a particular scene, it's worth checking that the iPhone isn't metering from a face that isn't there. 

Daylight. Low ISO

As we'd expect, the iPhone 5 is at its best in bright, sunny conditions. Although some luminance noise is visible in areas of plain tone (especially blue sky) detail capture is high, and exposure is almost always completely accurate. On the rare occasions when an image is completely 'off', exposure locking via touch and/or switching to HDR mode usually does the trick. 

Excellent detail in this ISO 50 shot - look at the diamond mesh of the fencing visible in the 100% crop to the right. 
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Even at base ISO sensitivity though, noise is obvious in areas of plain tone, like the blue sky in this shot. 
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At its best, detail capture from the 8MP iPhone 5 is hard to tell apart from dedicated cameras. Exposure is nice in this scene, too. 
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A tricky scene, taken under mixed artificial and natural light, but the resulting exposure is neutral, well-exposed and very detailed. 
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'Purple Haze'

Only a few days after the iPhone 5 became available, people began reporting an issue with a mysterious 'purple haze' appearing in photos taken with a bright light source just outside of the frame. There has been a lot of speculation to what may be causing this phenomenon. Some theories revolve around sensor blooming and chromatic abberation, some speculation centers on the new sapphire glass element in front of the lens.

The so-called 'purple haze' issue is most obvious when the adjacent area to the flare is quite dark, which is a scenario that is actually quite common in low light situations where you may have a single bright lamp in an otherwise dark room. It can also be triggered by shooting towords the sun, or with any particularly bright light source at or just beyond the edge of the frame. 

iPhone 5 - studio
iPhone 5 - outdoor (afternoon sun)

The most likely cause of the iPhone 5's purple haze is probably lens flare and internal reflections in the camera lens assembly. All lenses are succeptable to lens flare to some degree, and as you can see from the images at the top of this page, the iPhone 4S isn't immune either (ditto the iPhone 4 and competitive smartphones from other manufacturers).

For a detailed look at the so-called purple haze issue, take a look at our quick review of the iPhone 5's camera, published at dpreview.com.

Low Light, High ISO

Apple claims that the iPhone 5 offers improved low-light performance compared to the 4S. It certainly offers a more twilight-friendly ISO span, up to a nominal ISO 3200, compared to a maximum of ISO 1000 in the 4S. 

This shot was taken under artificial light, at ISO 800 with some daylight bleeding in from the window. As you can see, detail capture isn't as high as it is at ISO 80, in daylight, but it's not bad.
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This is an HDR shot, taken several hours after sunset, of the moon. At small sizes (web and social sharing) image quality is perfectly acceptable, but viewed close up it is obvious that at ISO 3200, resolution is relatively low. 
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This ISO 2500 shot is well-exposed, and white balance under street lighting is impressively neutral, but like the ISO 3200 image, above, pixel-binning is reducing critical resolution, as you can see form the 100% crop to the right.
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An ISO 800 shot taken under very challenging low-intensity halogen light. The color balance is unpleasantly magenta and low-contrast detail is somewhat smudgy, but resolution is noticably better than the pixel-binned output of ISO 1000 and above. 
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Compared to iPhone 4/4S

The camera modules of the 4S and 5 are different, but it seems likely that they're based on similar underlying hardware. From our testing we can see that the iPhone 5 is certainly applying more noise-reduction to areas of plain tone than the 4S, but up to ISO 1000, there's very little difference between the iPhone 5 and its predecessor.

This scene was lit with a single tungsten bulb. Focus was set manually (by touch) from the bauble in the center of the image. All three phones selected an ISO sensitivity of 800. 

Click on the thumbnails below for the full-sized original images.
iPhone 5 (100% crop - high contrast )
iPhone 5 (100% crop - midtone)
iPhone 4S (100% crop - high contrast )
iPhone 4S (100% crop - midtone)
iPhone 4 (100% crop - high contrast )
iPhone 4 (100% crop - midtone)

The iPhone 5's trump card in poor light, compared to the 4S, is its additional ISO sensitivity span, which goes up to ISO 3200. To get the iPhone 5 to shoot at its very highest ISO sensitivity settings, the light has to be extremely low. For the examples below, we moved our single tungsten light progressively further away from our still life, gradually decreasing the amount of light falling on the scene.

ISO 800
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ISO 2000
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Based on what we've seen here, and in our real-world shooting, it does look like the iPhone 5 employs pixel-binning at ISO settings higher than ISO 1000, and subsequently upsizes the resulting images to 3264x2448 pixels (8MP). Notice how sharpness drops signifncantly between ISO 800 and ISO 2000. This appears to be more than just increased noise and more aggressive noise-reduction.

Try as we might, we couldn't get the iPhone 5 to select ISO 1600 when capturing this scene, but in supplemental shooting we've established that the switch occurs between ISO 1000 and ISO 1250. Images captured at ISO 1000 are noisy but relatively sharp, and images at ISO 1250 and above are smoother, brighter, but much less detailed, suggesting a loss of true resolution (rather than just a masking, caused by noise and NR). Image quality remains extremely similar between ISO 2000-ISO 3200. 

This isn't a bad thing though - arguably in fact in a camera of this type it's quite the contrary. Although we'd love DSLR-level high ISO performance in a cameraphone, it's an unrealistic expectation. By combining the signals of neighboring photosites in this way, the iPhone can capture images in light much lower than its predecessor the iPhone 4S, and the drop in pixel-level image quality will probably be unnoticeable when the images are used for social and web use.