Because we couldn’t manually control the ISO setting on the iPhone 5S, we can't fully test the iPhone 5S in this situation. The 5S elected to take the shot below at ISO 320, which remains free of image noise, but where smudging of fine detail can already be seen. We'll look a further look into the iPhone 5S' ISO performance in the low-light section.
While the Z1 lets you choose ISO sensitivities from ISO 100, 200, 400 and 800 in Manual mode, we discovered that the smartphone either reports the setting wrongly in the EXIF data or it actually overrides the manual setting altogether. For example, in our indoor lab test, we shot at ISO 50, 100, 200, 400 and 800, but shooting at ISO 50 the camera records it as ISO 64, at ISO 800 the camera records it as ISO 1250 (which isn’t even selectable). This odd behavior happened again later when we went out to shoot in the real world.
In the 20MP captures we see again the strong appearance of image artifacts. They’re minimal at ISO 100, but come on strongly from ISO 200 onwards - they’re especially visible in the black areas of the image, as artificial looking checkered patterns, and we've posted some 100% crops to show you what we mean.
In the 8MP Superior Auto capture, the Z1 has opted to shoot at ISO 1250 (remember that in Superior Auto mode you can't change ISO settings), the appearance of image noise and the checkered pattern has been reduced but still remains visible.