Optical lens device of image scanner

An image scanner having optical lens device comprising:

• a scanning area, which may be available for supporting a document to be scanned;
• a light source, which may emit light to the scanning area for generating optical image of the document;
• a light-guiding device, which includes at least one piece of reflective mirror for making the optical image proceed at least once reflection and guides the reflected optical image toward a predetermined direction;
• an optical lens device, which receives the optical image transferred from the light-guiding device and focuses it into image;
• an image induction element, which is just located at the position corresponding to the place where the optical image is focused into an image;
• wherein, the optical lens device at least includes:
• a diaphragm and plural lenses, which are arranged linearly with the diaphragm and the image induction element for defining an optical path between the document and the image induction element wherein, among the plural lenses, the one that is most close to the document is called the first lens, while the other one that is most close to the image induction element is called the last lens, and the distance that is between the last lens and the image induction element is abbreviated as BFL, and the length, of the induced image, provided by the image induction element is called the image height, and the distance between the document and the image induction element is abbreviated as TT, and the effective focus length of the optical lens device is abbreviated as EFL;
• wherein, the ratio between the diameter of the last lens of the optical lens device and the diameter of the first lens is greater than one;
• that is, the diameter of the last lens/the diameter of the first lens>1.