Testing Camera Image Sharpness - Nokia RM-779 Service Manual

RM-779
Camera Module Troubleshooting
If large dust particles get trapped on top of the lens surface in the cavity between camera window and lens,
they will cause image blurring and poor contrast. The dust gasket between the window and lens 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 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 four possible sources for the problem:
1 The protection window is fingerprinted, soiled, dirty, visibly scratched or broken.
2 The user has tried to take pictures in too dark conditions and the images are blurred due to handshake
or movement. This is not a cause to replace the camera module.
3 There is dirt between the protection window and the camera lens.
4 The protection window is defective. This can be either a manufacturing failure or caused by the user. The
window should be changed.
5 The target is closer than 50 cm, the camera sharp area starts from 50 cm.
A quantitative analysis of sharpness is very difficult to conduct in any other environment than optics
laboratory. Therefore, subjective analysis should be used.
If no visible defects (items 1-4) are found, a couple of test images should be taken. Generally, a well-
illuminated typical indoor scene, such as the one in Figure "Good image taken indoors", can be used as a
target. The main considerations are:
• The protection window has to be clean.
• The amount of light (300 – 600 lux (bright office lighting)) is sufficient.
• The scene should contain, for example, small objects for checking sharpness. Their distance should be 1
– 2 meters.
• If possible, compare the image to another image of the same scene, taken with a different device. Note
that the reference device has to be a similar Nokia phone.
Issue 1
Figure 37 Effects of dust on optical path
COMPANY CONFIDENTIAL
Copyright © 2011 Nokia. All rights reserved.
Page 5 – 11