Testing Camera Image Sharpness - Nokia N72 Service Manual

RM-180
Camera Module Troubleshooting
Black spots in an image are caused by dirt particles trapped inside the optical system. Clearly visible and
sharp edged black dots in an image are typically dust particles on the image sensor. These spots are searched
for in the manufacturing phase, but it is possible that the camera body cavity contains a particle, which may
move onto the image sensor active surface, for example, when the phone is dropped. Therefore it is also
possible that the problem will disappear before the phone is brought to service. The camera should be
replaced if the problem is present when the service technician analyses the phone.
If dust particles are lying on the infrared filter surface on either side, they are hard to locate because they
are out of focus, and appear in the image as large, grayish and fading-edge 'blobs'. Sometimes they are
invisible to the eye, and the user probably does not notice them at all. However, it is possible that a larger
particle disturbs the user, causing need for service.
If large dust particles get trapped on top of the lens surface in the cavity between the camera window and
the lens, they will cause image blurring and poor contrast. If dust stays on the camera module surface, camera
cussion, camera bezel or window at assembling, dust may sneak into the optical system as the optical zoom
or Auto focus lens moves back and forth. The camera cussion and bezel between the window and the lens
unit or camera module should prevent any particles from getting into the cavity after the manufacturing
phase.
If dust particles are found on the sensor, this is classified as a manufacturing error of the module, and the
camera should be replaced. Any particles inside the cavity between the protection window and the lens have
most probably been trapped there in the assembly phase at a Nokia factory. Unauthorized disassembling of
the product can also be the root of the problem. However, in most cases it should be possible to remove the
particle(s) by using clean compressed air. Never wipe the lens surface before trying compressed air; the
possibility of damaging the lens is substantial. Always check the image sharpness after removing dust.

Testing camera image sharpness

Symptoms and diagnosis
If pictures taken with a device are claimed to be blurry, there are six possible sources for the problem:
1 The protection window is fingerprinted, soiled, dirty, visibly scratched or broken.
2 The photographed object is too close – the camera lens operates with distances from 64 cm to infinity.
This is no cause to replace camera module.
3 User has tried to take pictures in too dark conditions, and images are blurred due to handshake or
movement. This is no cause to replace camera module.
4 There is dirt between the protection window and camera lens.
Issue 1
Figure 75 Effects of dust on optical path
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