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 ISO 3200, compared to a maximum of ISO 1000 in the 4S. Let's take a detailed look.
The camera modules of the 4S and 5 are different, but it seems likely that they're based on similar underlying hardware. The iPhone 5 is certainly applying more noise-reduction to areas of plain tone than the 4S, but up to ISO 1600, there's very little difference between the two cameras.
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 (automatically - you can't control ISO manually). 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, decreasing the amount of light falling on the scene.
|iPhone 5, ISO 800||100% Crop|
|iPhone 5, ISO 2000||100% Crop|
|iPhone 5, ISO 3200||100% Crop|
Well, there we have it. The iPhone 5's sensor isn't magically more sensitive than its predecessor after all. There have been rumors of pixel-binning and multi-shot noise reduction at play in the iPhone 5, and based on what we've seen, it does look like the iPhone 5 employs some sort of pixel-binning at its highest ISO sensitivities, and upsizes the resulting images to 3264x2448 pixels (8MP). Notice how sharpness drops significantly 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 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 of detail, caused by noise and NR).
This isn't a bad thing though. 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.
Interestingly, right now this 'boost' mode is not available when running third-party camera applications on the iPhone 5. But according to a recent report, app developers will have the option of activating it if they desire, and it is likely that the next round of updates to popular apps like Camera+ and Instagram will be able to take advantage of the new high-sensitivity mode in the near future.
Camera phones are not well known for their flash capability. Some have real xenon flash strobes, but most are nothing more than a very bright LED. The iPhone 4, 4S and 5 all feature LED flashes, and while none can match the flashes of even cheap compact cameras for output power, they can come in handy for close-range social portraits.
Looking at the crops of our subject's eye it is easy to see the affect of the iPhone 5's more aggressive noise reduction. The eyebrows and lashes are ever so slightly less well defined. Red eye is something that plagues all 3 cameras equally and in the default Apple camera app there is no option for red eye reduction. There is however a fairly decent red eye removal function available via the Edit options dialog on the iPhone.
For both the iPhone 5 and 4s the camera chose an ISO setting of 80. However the 4 chose a much higher ISO of 250 while keeping the same shutter speed as the other 2 cameras (~1/15s) which has resulted in a brighter image for the iPhone 4. As a consequence, the iPhone 4 has given a noisier image, but the moderate grittiness is not objectionable.