Nokia N900 Service Manual

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Introduction to camera module troubleshootingBackground, tools and terminologyFaults or complaints in camera operation can be roughly categorised into three subgroups:1 Camera is not functional at all; no image can be taken.2 Images can be taken but there is nothing recognizable in them.3 Images can be taken and they are recognizable but for some reason the quality of images is seriouslydegraded, or customer complains about image quality.Image quality is very hard to measure quantitatively, and even comparative measurements are difficult(comparing two images) to do, if the difference is small. Especially if the user is not satisfied with his/herdevice's image quality, and tells, for example, that the images are not sharp, it is fairly difficult to accuratelytest the device and get an exact figure which would tell whether the device is functioning properly.Often subjective evaluation has to be used for finding out if a certain property of the camera is acceptableor not. Some training or experience of a correctly operating reference device may be needed in order todetect what actually is wrong, or is there anything wrong at all.It is easy for the user to take bad images in bad conditions. Therefore the camera operation has to be checkedalways in constant conditions (lighting, temperature) or by using a second, known-to-be good device asreference. Experience helps significantly in analysing image quality.TermsAutofocus Camera module contains lens movement mechanics for focus adjustment.Autofocus enables camera to take sharp images of objects positionedbetween 10cm to infinity. During AF the viewfinder image will bemomentarily blurred as the camera searches for the right focus setting.Digital zoom Digital zoom is done by first cropping the image by the zoom ratio andthen upscaling it to the output resolution. This will decrease the imagequality especially with high zoom ratios.Dynamic range Camera's ability to capture details in dark and bright areas of the scenesimultaneously.Exposure time Camera modules use silicon sensor to collect light and for forming animage. The imaging process roughly corresponds to traditional filmphotography, in which exposure time means the time during which thefilm is exposed to light coming through optics. Increasing the time willallow for more light hitting the film and thus results in brighter image. Theoperation principle is exactly the same with silicon sensor, but the shutterfunctionality is handled electronically i.e. there is no mechanical movingparts like in film cameras.Flicker Phenomenon, which is caused by pulsating in scene lighting, typicallyappearing as wide horizontal stripes in an image.ND-filter Neutral density filter is a filter which is used in very bright conditions toreduce the amount of light hitting the sensor. The filter is built into thecamera module and applied automatically when needed.Noise Variation of response between pixels with same level of input illumination.Resolution Usually the amount of pixels in the camera sensor. In some occasions theterm resolution is used for describing the sharpness of the images.RX-51Camera Module TroubleshootingIssue 1 COMPANY CONFIDENTIAL Page 5 –5Copyright © 2009 Nokia. All rights reserved.