The Nokia 808 PureView is a Symbian-powered smartphone first unveiled on 27 February 2012 at the Mobile World Congress. It is the first smartphone to feature Nokia's PureView Pro technology, a pixel oversampling technique that reduces an image taken at full resolution into a lower resolution picture, thus achieving higher definition and light sensitivity, and enables lossless zoom. It was one of the most advanced camera phones at the time of its release in May 2012.
The Nokia 808 features a 41 megapixel 1/1.2 in (10.67 × 8 mm) sensor and a high-resolution f/2.4 Zeiss all-aspherical 1-group lens. The 808's sensor was the largest (over 4 times larger than typical compact cameras) sensor ever to be used in a cameraphone at the time of its launch, a record previously held by Nokia's N8 and, as of September 2014, by the Panasonic Lumix CM1. The 808's sensor remains the highest resolution sensor ever to be used in a cameraphone.
The 808 won the award for "Best New Mobile Handset, Device or Tablet" at Mobile World Congress 2012, and the award for Best Imaging Innovation for 2012 from the Technical Image Press Association. It was also given a Gold Award by Digital Photography Review.
On 24 January 2013, Nokia officially confirmed the 808 Pureview to be the last Symbian smartphone. In July 2013, Nokia released the Lumia 1020, a successor running the Windows Phone operating system common to Nokia's newer products.
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PureView Pro camera
PureView Pro is an imaging technology used in the Nokia 808 PureView device. It is the combination of a large 1/1.2 in, very high-resolution 41 MP image sensor with high-performance Carl Zeiss optics. The large sensor enables pixel oversampling, which means the combination of many sensor pixels into one image pixel. PureView imaging technology delivers high image quality, lossless zoom and improved low light performance (see below). It dispenses with the usual scaling/interpolation model of digital zoom commonly used in other smartphones, as well as optical zoom used in most digital cameras, where a series of lens elements moves back and forth to vary the magnification and field of view. In both video and stills, this technique provides greater zoom levels as the output picture size reduces.
Image sensor
The Nokia 808 has a 41.3 megapixel 1/1.2 in CMOS FSI image sensor with 7728x5368 pixels. Pixel size is 1.4 µm; sensor size is 10.67 × 8.00 mm.
Depending on the aspect ratio chosen by the user, the sensor will use either 7728x4354 pixels (33.6 MP) for 16:9 images, or 7152x5368 pixels (38.4 MP) for 4:3 images when using the default camera software, although third-party apps exist that can capture the full resolution of the sensor. The output from the sensor is processed using the on-chip image processor, resulting in a lower-resolution image with pixel oversampling, lossless digital zoom, or a combination of both. The image processor highly reduces external processing needs and data rates as well as image noise (see noise shaping). At default settings, maximum zoom is 3x for stills (5 MP in a 16:9 aspect ratio) and 4x for video (1080p).
Zoom
Zoom is digital but retains a high resolution due to the 41 MP sensor. The limit of the zoom is reached when the selected output resolution becomes the same as the input resolution. That means once the area of the sensor reaches 3072x1728, the zoom limit is reached. So the zoom always provides the true image resolution the user wants. The level of pixel oversampling is highest when zoom is not used. It gradually decreases until the maximum zoom is hit, where there is no oversampling. At this stage, PureView Pro optics and pixels start behaving in a more conventional way. But because only the centre of the optics is used, the best optical performance is achieved - including low distortion, no vignetting and highest levels of resolved detail. This also means that at full digital zoom, the noise reduction achieved by oversampling (pixel binning) is lost as no oversampling happens at full zoom.
Autofocus
PureView Pro features continuous autofocus in all shooting modes, close-up (Macro) focus, face detection, touch focus with easy manually selected focus point and hyperfocal distance focus for defined depth of field, for extreme focus speed or when reliably achieving focus is not possible.
Video
The on-chip oversampling image processor of the 808 enables oversampling of all 38 megapixels even at the high video data rates of 1080p with 30 fps. Maximum possible zoom is 4x for 1080p, 6x for 720p HD and 12x for nHD (640x360) video. In addition, encoding is up to 25 Mbps in 1080p H.264/MPEG-4 HD video format. The PureView Pro sensor integrates a special video processor that handles pixel scaling at up to 1 billion pixels per second before sending the required number to the main image processor.
Lens
The 808 has Carl Zeiss 5-element 1-group lens with f/2.4 aperture and 8.02 mm focal length (35 mm equivalent focal length is 26 mm in 16:9 and 28 mm in 4:3 aspect ratio). Focus range is from 15 cm to infinity (throughout the zoom range).
The optics are based on a shiftable fixed-focus lens; similar to the prime lenses in most Zeiss Planar or Tessar optics, focus is achieved by varying the distance to the image sensor (unit focusing lens). This construction has the advantage that no movable focus group is needed. Considerable movable (focus-range) lens groups need a minimum of one additional adaptive lens element in both the moved group and the stationary group, increasing the number of elements by at least two. This increases unwanted reflections as well as overall tolerances and therefore decreases sharpness.
The lens consists of only 1 group with molded elements, which gives a highly stable, precise mechanical alignment. The lenses are partly made of plastic, which provides sufficient stability at this size and as a 1-group lens and has the significant advantage of making it possible to use extreme aspheric shaped lens elements.
5 all-aspherical lens elements are used, making it possible to increase border-sharpness and lower distortion and astigmatism. The high-refractive index, low-dispersion glass additionally helps reduce chromatic aberrations. A neutral density filter with approximately ND8 (3 f-stops) is employed for shooting in high light levels where normally a smaller aperture would be set. Although the lens is named a Tessar, it has almost nothing in common with the 4 element in 3 group, non-aspherical original Tessar.
Due to the comparatively large 1/1.2 in sensor and the comparatively fast lens with f/2.4 aperture, the camera has a quite shallow depth of field, equivalent to approximately f/7.8 at 26 mm on 35 mm full-frame.
Shutter
The 808 has a mechanical shutter with short shutter lag and ND8 (3 f-stops) neutral density filter.
Audio
The 808 PureView employs Dolby Headphone software to transform stereo content to surround via a 3.5 mm A/V jack. It also includes Dolby Digital Plus software to provide 5.1 surround sound via HDMI or DLNA. The dual software elements from Dolby are embedded into the Nokia Belle feature pack 1 OS.
The 808 PureView is the first device to include the Nokia Rich Recording technology and has a frequency range between 25 Hz to around 19 kHz. The 808 PureView can capture sounds at the loudness level of up to 145 decibels without distortion. The two microphones, located at the top and the bottom enable ambient stereo recording. The audio encoding is done in AAC high profile, 256 kbit/s, 48000 Hz.
Source of the article : Wikipedia
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