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Apple support document addresses iPhone 5 'purple haze'

Purple flare around sun. | Source: weaksauce12 via Twitter

Apple has publicly explained an issue that can result in a purple "haze" or flare that users have discovered can show up in pictures taken with the new iPhone 5.

The official support document posted on Apple's site is entitled "iPhone: Camera image effects." It notes that users may sometimes see "a purplish or other colored flare, haze, or spot" in an image with an "out-of-scene bright light."

"Most small cameras, including those in every generation of iPhone, may exhibit some form of flare at the edge of the frame when capturing an image with out-of-scene light sources," the offered resolution states. "This can happen when a light source is positioned at an angle (usually just outside the field of view) so that it causes a reflection off the surfaces inside the camera module and onto the camera sensor.

"Moving the camera slightly to change the position at which the bright light is entering the lens, or shielding the lens with your hand, should minimize or eliminate the effect."

Days after the iPhone 5 was released, the so-called "purple haze" issue was noted by users online. While some speculated it could be related to a defect with the phone, further investigation revealed the problem is common with many modern digital cameras, especially miniaturized devices.

At issue is a lens array's refractive index which numerically represents the manner in which light, or more specifically wavelengths of light, moves through the optics system. Ideally, a lens will focus all colors, or wavelengths, at a single point on the focal plane, thus creating a near-perfect replication of an image. In practice, however, lenses don't allow for wavelengths to meet at a convergence point, creating what is called chromatic aberration.

Due to a number of factors, including reference tuning, architecture of digital sensors and relatively short focal lengths in smaller camera systems, chromatic aberration usually presents itself in shorter wavelengths like violet.

High-end lenses can be adjusted to deal with axial chromatic aberrations, those that cause color fringing, and are called apochromatic lenses, though these types of systems are costly and bulky as additional glass elements are added to the array. Another form of compensating for the distortion are aspherical lenses that are specially designed to reform light to achieve more accurate focus. These elements are also costly, however, as a multitude of steps are needed to manufacture the glass.