Nokia RM-626 Service Manual Download Page 177

Page: 177 / 244

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 five possible sources for the problem:
1 The protection window is fingerprinted, soiled, dirty, visibly scratched or broken.
2 The camera module has failed to focus correctly, producing a blurred image.
3 User has tried to take pictures in too dark conditions and images are blurred due to handshake or

movement. This is not a cause to replace camera module.

4 There is dirt between the protection window and the camera lens.
5 The protection window is defective. This can be either a manufacturing failure or caused by the user. The

window should be changed.

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.

The taken images should be analysed on PC screen at 100% scaling simultaneously with a reference image.

Pay attention to the computer display settings; at least 65000 colors (16 bit) have to be used. 256 (8-bit)

color setting is not sufficient; true color (24 bit, 16 million colors) or 32 bit (full color) setting is recommended.
If the differences are noticeable at a glance and also if the one under investigation is significantly inferior,

the module might have a faulty lens. In this case, the module should be changed. Always re-check the

resolution after changing the camera module. If a different module produces a clearly noticeable quality gap,

the fault is probably in the camera window. Check the window by looking carefully through it when replacing

the module. As references Figure "Good image taken indoors" and Figure "Good image taken outdoors" can

be used. Another possibility is to use a service point comparison phone, if available.

Effects of dirty or defective camera lens protection window

The following series of images demonstrates the effects of fingerprints on the camera protection window.

Note:

The effects of any dirt in images can vary very much; it may be difficult to judge if the window

has been dirty when some image has been taken or if something else has been wrong. That is why

the cleanness of the protection window should always be checked and the window should be wiped

clean with a suitable cloth.