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 (Page )
", can be used as a target. The
main considerations are:
• The camera module has to be given time to focus correctly. Correct focusing is normally indicated with a
flashing icon or green bracket in the viewfinder. During focusing the image in the viewfinder will move
slightly back and fourth, this is normal and shows that the lens unit is moving. During the movement a faint
sound can be heard from the camera head.
• 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.
There are several conditions in which AF operation is challenging for the camera module, these include:
• Low light scenes and night mode
• Scenes with low contrast
• Fast-moving objects
Under low light and night mode the AF function is slower than under good light, it may even fail to find correct
focus position. Low contrast scenes and fast moving objects may also slow down or cause AF to fail. This is
normal operation and no cause to replace camera.
AF operation may be tested by taking images of objects at different distances. Good distances are 20 cm, 60 cm
and infinity (>3 m). Any LED or xenon flashes should not be used while taking the images.
The taken images should be analysed on PC screen at 100% scaling simultaneously with reference image. Pay
attention to the computer display settings; at least 65000 colours (16 bit) have to be used. 256 (8-bit) colour
setting is not sufficient, and true colour (24 bit, 16 million colours) or 32 bit (full colour) setting is recommended.
If there appears to be a clearly noticeable difference between the reference image and the test images, the
module might have faulty lens. In this case, the module should be changed. Always re-check the resolution after
changing the camera. If a different module produces the same result, the fault is probably in camera window.
Check the window by looking carefully through it when replacing the module. As references Figure "
Good image taken outdoors (Page )
" can be used. Another possibility is to
use 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.
RM-42
Camera Module Troubleshooting
Nokia Customer Care
9241872 (Issue 1)
Company Confidential
Page 8–13
Copyright ©2005 Nokia. All Rights Reserved.
