Canon BJC 50 Service Manual - Page 135

BJC-50 6.2 Scanner Cartridge Structure Slit Mirror Part 4: Technical Reference BASIS Field Lens 2 Imaging Lens BASIS Mirror Field Lens Scanning Document Platen LED Diffusion Board Illumination Lens PCB Imaging Lens Diffusion Board Illumination Lens LEDs Figure 4-34 Scanner Cartridge 1) LED Red, green and blue LEDs are used to illuminate the scanning document. To Compensate for the low intensity of the red and green LED's, two red and green LEDs have been incorporated and a total of five LEDs are mounted on the scanner. Only the green LED is used for monochrome scanning. 2) Illumination lens This "D" shaped lens converges the light from the LED light source. 3) Diffusion board The light intensity of the LED is brighter at the center than at the ends. The diffusion board allows even distribution of light onto the document. 4) Field lens This lens prevents any magnification reduction caused by paper gaps when scanning a lifted or bent document. 5) Imaging lens This lens is used for forming an image of the light rays converged by the field lens onto the BASIS. 6) Shading board The shading board with a slit at the front surface of the BASIS is used to prevent crosstalk generated in areas adjacent to high contrast areas. 7) BASIS The scanner cartridge uses a semiconductor type, one-line 128 pixel BASIS (BaseStored Image Sensor). Depending on the light amount of the image formed on the BASIS, electric voltage signals are sent to the scanner controller as image signals. 4-47