Image forming lens, image forming lens unit, original document reading module, apparatus and method, and image information processing apparatus

An image forming lens for forming an image of an original document, comprising:

• a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens;
• and
• a rear side lens group constituted of one negative lens and arranged at an image forming side,
• wherein an outer shape of the rear side lens group has a rotational asymmetry with respect to an optical axis of the image forming lens,
• wherein a back-focus of the image forming lens in an actual usage state thereof is equal to or smaller than 25% of an entire length of the image forming lens, and an air space between the front side lens group and the rear side lens group is equal to or greater than 50% of the entire length of the image forming lens.

An original document reading module for forming an image of an original document and converting image information of the image into electrical signals, comprising:

• an image forming lens configured to form the image of the original document, the image forming lens including a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens,
• a rear side lens group constituted of one negative lens and arranged at an image forming side, and
• a supporting device configured to support each lens of the front side lens group and the rear side lens group and to integrate the front side lens group and the rear side lens group with each other, the supporting device including a front side lens group supporting device configured to support the front side lens group, the front side lens group supporting device being rotatable relative to the rear side lens group supporting device around an optical axis of the image forming lens, a rear side lens group supporting device configured to support the rear side lens group, and a connecting device configured to connect the front side lens group supporting device and the rear side lens group supporting device with each other so as to be integrated with each other,
• a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens, and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens;
• and
• a light receiving element array configured to photo-electrically convert image information of the image of the original document formed thereupon by the image forming lens into the electrical signals.

An original document reading apparatus, comprising:

• a scanning device configured to scan an original document;
• a light receiving element array configured to photo-electrically convert image information of an image formed thereupon into electrical signals;
• an image forming lens configured to image a light flux from the original document being scanned by the scanning device so as to form an image of the original document on the light receiving element array, the image forming lens including a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens, and a rear side lens group constituted of one negative lens and arranged at an image forming side, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens;
• a signal processing device configured to process the electrical signals of the light receiving element array;
• and
• an image processing device configured to apply image processing to the electrical signals processed by the signal processing device.

An original document reading apparatus, comprising:

• a scanning device configured to scan an original document;
• a light receiving element array configured to photo-electrically convert image information of an image formed thereupon into electrical signals;
• an image forming lens configured to image a light flux from the original document being scanned by the scanning device so as to form an image of the original document on the light receiving element array, the image forming lens including a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens, and a rear side lens group constituted of one negative lens and arranged at an image forming side, an outer shape of the rear side lens group of the image forming lens having a rotational asymmetry with respect to an optical axis of the image forming lens, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens;
• a signal processing device configured to process the electrical signals of the light receiving element array;
• and
• an image processing device configured to apply image processing to the electrical signals processed by the signal processing device.

An original document reading apparatus, comprising:

• a scanning device configured to scan an original document;
• a light receiving element array configured to photo-electrically convert image information of an image formed thereupon into electrical signals;
• an image forming lens unit, the image forming lens unit comprising an image forming lens configured to image a light flux from the original document being scanned by the scanning device so as to form an image of the original document on the light receiving element array, the image forming lens including a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens, and a rear side lens group constituted of one negative lens and arranged at an image forming side, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens, and
• a supporting device including a front side lens group supporting device configured to support the front side lens group, a rear side lens group supporting device configured to support the rear side lens group, and a connecting device configured to connect the front side lens group supporting device and the rear side lens group supporting device with each other so as to be integrated with each other, the front side lens group supporting device being rotatable relative to the rear side lens group supporting device around an optical axis of the image forming lens;
• a signal processing device configured to process the electrical signals of the light receiving element array;
• and
• an image processing device configured to apply image processing to the electrical signals processed by the signal processing device.

An original document reading apparatus, comprising:

• a scanning device configured to scan an original document;
• a light receiving element array configured to photo-electrically convert image information of an image formed thereupon into electrical signals;
• an image forming lens configured to image a light flux from the original document being scanned by the scanning device so as to form an image of the original document on the light receiving element array, the image forming lens including a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens, a rear side lens group constituted of one negative lens and arranged at an image forming side, and a shading device, which is configured to correct brightness of an image at an image surface of the image forming lens with respect to a main scanning direction, between the front side lens group and the rear side lens group, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens;
• a signal processing device configured to process the electrical signals of the light receiving element array;
• and
• an image processing device configured to apply image processing to the electrical signals processed by the signal processing device.

An original document reading apparatus, comprising:

• a scanning device configured to scan an original document;
• a light receiving element array configured to photo-electrically convert image information of an image formed thereupon into electrical signals;
• an image forming lens configured to image a light flux from the original document being scanned by the scanning device so as to form an image of the original document on the light receiving element array, the image forming lens including a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens, a rear side lens group constituted of one negative lens and arranged at an image forming side, and a folding mirror configured to bend an optical path of the image forming lens, between the front side lens group and the rear side lens group, the folding mirror having a reflecting surface of a predetermined shape and configured to function as a shielding device to correct brightness of an image at an image surface of the image forming lens with respect to a main scanning direction, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens;
• a signal processing device configured to process the electrical signals of the light receiving element array;
• and
• an image processing device configured to apply image processing to the electrical signals processed by the signal processing device.

An original document reading apparatus, comprising:

• a scanning device configured to scan an original document;
• a light receiving element array configured to photo-electrically convert image information of an image formed thereupon into electrical signals;
• an image forming lens configured to image a light flux from the original document being scanned by the scanning device so as to form an image of the original document on the light receiving element array, the image forming lens including a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens, and a rear side lens group constituted of one negative lens and arranged at an image forming side, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens,
• the image forming lens and the light receiving element array being integrated with each other so as to form an original document reading module;
• a signal processing device configured to process the electrical signals of the light receiving element array;
• and
• an image processing device configured to apply image processing to the electrical signals processed by the signal processing device.

An image information processing apparatus, comprising:

• an original document reading device for forming an image of an original document and converting image information of the image into electrical signals, the original document reading device including;
• a scanning device configured to scan the original document,
• a light receiving element array configured to photo-electrically convert image information of an image formed thereupon into electrical signals;
• an image forming lens configured to image a light flux from the original document being scanned by the scanning device so as to form the image of the original document on the light receiving element array, the image forming lens including a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens, and a rear side lens group constituted of one negative lens and arranged at an image forming side, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens, and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens,
• a signal processing device configured to process an output signal of the light receiving element array, and
• an image processing device configured to apply image processing to the signal processed by the signal processing device;
• and
• an outputting device configured to output the electrical signals of the original document reading device.

An image information processing apparatus, comprising:

• an original document reading device for forming an image of an original document and converting image information of the image into electrical signals, the original document reading device including;
• a scanning device configured to scan the original document,
• a light receiving element array configured to photo-electrically convert image information of an image formed thereupon into electrical signals;
• an image forming lens configured to image a light flux from the original document being scanned by the scanning device so as to form the image of the original document on the light receiving element array, the image forming lens including a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens, and a rear side lens group constituted of one negative lens and arranged at an image forming side, an outer shape of the rear side lens group of the image forming lens having a rotational asymmetry with respect to an optical axis of the image forming lens, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens, and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens,
• a signal processing device configured to process an output signal of the light receiving element array, and
• an image processing device configured to apply image processing to the signal processed by the signal processing device;
• and
• an outputting device configured to output the electrical signals of the original document reading device.

An image information processing apparatus, comprising:

• an original document reading device for forming an image of an original document and converting image information of the image into electrical signals, the original document reading device including;
• a scanning device configured to scan the original document,
• a light receiving element array configured to photo-electrically convert image information of an image formed thereupon into electrical signals;
• an image forming lens unit comprising an image forming lens configured to image a light flux from the original document being scanned by the scanning device so as to form the image of the original document on the light receiving element array, the image forming lens including a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens, a rear side lens group constituted of one negative lens and arranged at an image forming side, and a supporting device including a front side lens group supporting device configured to support the front side lens group, a rear side lens group supporting device configured to support the rear side lens group, and a connecting device configured to connect the front side lens group supporting device, the front side lens group supporting device being rotatable relative to the rear side lens group supporting device around an optical axis of the image forming lens, and the rear side lens group supporting device with each other so as to be integrated with each other, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens, and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens,
• a signal processing device configured to process an output signal of the light receiving element array, and
• an image processing device configured to apply image processing to the signal processed by the signal processing device;
• and
• an outputting device configured to output the electrical signals of the original document reading device.

An image information processing apparatus, comprising:

• an original document reading device for forming an image of an original document and converting image information of the image into electrical signals, the original document reading device including;
• a scanning device configured to scan the original document,
• a light receiving element array configured to photo-electrically convert image information of an image formed thereupon into electrical signals;
• an image forming lens configured to image a light flux from the original document being scanned by the scanning device so as to form the image of the original document on the light receiving element array, the image forming lens including a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens, a rear side lens group constituted of one negative lens and arranged at an image forming side, and a shading device, which is configured to correct brightness of an image at an image surface of the image forming lens with respect to a main scanning direction, between the front side lens group and the rear side lens group, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens, and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens,
• a signal processing device configured to process an output signal of the light receiving element array, and
• an image processing device configured to apply image processing to the signal processed by the signal processing device;
• and
• an outputting device configured to output the electrical signals of the original document reading device.

An image information processing apparatus, comprising:

• an original document reading device for forming an image of an original document and converting image information of the image into electrical signals, the original document reading device including;
• a scanning device configured to scan the original document,
• a light receiving element array configured to photo-electrically convert image information of an image formed thereupon into electrical signals;
• an image forming lens configured to image a light flux from the original document being scanned by the scanning device so as to form the image of the original document on the light receiving element array, the image forming lens including a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens, a rear side lens group constituted of one negative lens and arranged at an image forming side, and a folding mirror configured to bend an optical path of the image forming lens, between the front side lens group and the rear side lens group, the folding mirror having a reflecting surface of a predetermined shape and is configured to function as a shielding device to correct brightness of an image at an image surface of the image forming lens with respect to a main scanning direction, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens, and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens,
• a signal processing device configured to process an output signal of the light receiving element array, and
• an image processing device configured to apply image processing to the signal processed by the signal processing device;
• and
• an outputting device configured to output the electrical signals of the original document reading device.

An image information processing apparatus, comprising:

• an original document reading device for forming an image of an original document and converting image information of the image into electrical signals, the original document reading device including;
• a scanning device configured to scan the original document,
• a light receiving element array configured to photo-electrically convert image information of an image formed thereupon into electrical signals;
• an image forming lens configured to image a light flux from the original document being scanned by the scanning device so as to form the image of the original document on the light receiving element array, the image forming lens including a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens, and a rear side lens group constituted of one negative lens and arranged at an image forming side, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens, and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens,
• the image forming lens and the light receiving element array being integrated with each other so as to form an original document reading module,
• a signal processing device configured to process an output signal of the light receiving element array, and
• an image processing device configured to apply image processing to the signal processed by the signal processing device;
• and
• an outputting device configured to output the electrical signals of the original document reading device.

An image information processing apparatus, comprising:

• an original document reading device for forming an image of an original document and converting image information of the image into electrical signals, the original document reading device including;
• a scanning device configured to scan the original document,
• a light receiving element array configured to photo-electrically convert image information of an image formed thereupon into electrical signals;
• an image forming lens configured to image a light flux from the original document being scanned by the scanning device so as to form the image of the original document on the light receiving element array, the image forming lens including a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens, a rear side lens group constituted of one negative lens and arranged at an image forming side, and a supporting device including a front side lens group supporting device configured to support the front side lens group, the front side lens group supporting device being rotatable relative to the rear side lens group supporting device around an optical axis of the image forming lens, a rear side lens group supporting device configured to support the rear side lens group, and a connecting device configured to connect the front side lens group supporting device and the rear side lens group supporting device with each other so as to be integrated with each other, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens, and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens,
• a signal processing device configured to process an output signal of the light receiving element array, and
• an image processing device configured to apply image processing to the signal processed by the signal processing device;
• and
• an outputting device configured to output the electrical signals of the original document reading device.

An image information processing apparatus, comprising:

• an original document reading device for forming an image of an original document and converting image information of the image into electrical signals, the original document reading device including;
• a scanning device configured to scan the original document,
• a light receiving element array configured to photo-electrically convert image information of an image formed thereupon into electrical signals;
• an image forming lens configured to image a light flux from the original document being scanned by the scanning device so as to form the image of the original document on the light receiving element array, the image forming lens including a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens, a rear side lens group constituted of one negative lens and arranged at an image forming side, and a shading device, which is configured to correct brightness of an image at an image surface of the image forming lens with respect to a main scanning direction, between the front side lens group and the rear side lens group, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens, and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens,
• a signal processing device configured to process an output signal of the light receiving element array, and
• an image processing device configured to apply image processing to the signal processed by the signal processing device;
• and
• an outputting device configured to output the electrical signals of the original document reading device.

An image forming lens for forming an image of an original document, comprising:

• a front side lens group having 2 or more lenses and arranged at an object side, said 2 or more lenses including at least one positive lens;
• and
• a rear side lens group constituted of one negative lens and arranged at an image forming side,
• wherein a back-focus of the image forming lens in an actual usage state thereof is equal to or smaller than 25% of an entire length of the image forming lens, and an air space between the front side lens group and the rear side lens group is equal to or greater than 50% of the entire length of the image forming lens, and
• wherein the rear side lens group includes at least one anamorphic surface.

An image forming lens for forming an image of an original document, comprising:

• a front side lens group having 2 or more lenses and arranged at an object side, said 2 or more lenses including at least one positive lens;
• and
• a rear side lens group constituted of one negative lens and arranged at an image forming side,
• wherein a back-focus of the image forming lens in an actual usage state thereof is equal to or smaller than 25% of an entire length of the image forming lens, and an air space between the front side lens group and the rear side lens group is equal to or greater than 50% of the entire length of the image forming lens, and
• wherein the rear side lens group includes at least one anamorphic surface, and wherein a curved line, which is formed when the anamorphic lens surface of the rear side lens group crosses a flat plane including an optical axis of the rear side lens group, is formed in a non-arc shape.

An image forming lens for forming an image of an original document, comprising:

• a front side lens group having 2 or more lenses and arranged at an object side, said 2 or more lenses including at least one positive lens;
• and
• a rear side lens group constituted of one negative lens and arranged at an image forming side, wherein an outer shape of the rear side lens group has a rotational asymmetry with respect to an optical axis of the image forming lens,
• wherein a back-focus of the image forming lens in an actual usage state thereof is equal to or smaller than 25% of an entire length of the image forming lens, and an air space between the front side lens group and the rear side lens group is equal to or greater than 50% of the entire length of the image forming lens, and
• wherein the rear side lens group includes at least one anamorphic surface.

An original document reading module for forming an image of an original document and converting image information of the image into electrical signals, comprising:

• an image forming lens configured to form the image of the original document, the image forming lens including a front side lens group having 2 or more lenses and arranged at an object side, said 2 more lenses including at least one positive lens, and a rear side lens group constituted of one negative lens and arranged at an image forming side, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens, an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens, and the rear side lens group including at least one anamorphic surface;
• and
• a light receiving element array configured to photo-electrically convert the image information of the image of the original document formed thereupon by the image forming lens into the electrical signals,
• wherein the rear side lens group and the light receiving element array are integrated with each other.

An original document reading apparatus for forming an image of an original document and converting image information of the image into electrical signals, comprising:

• an image forming lens configured to form the image of the original document, the image forming lens including a front side lens group having 2 or more lenses and arranged at an object side, said 2 more lenses including at least one positive lens, and a rear side lens group constituted of one negative lens and arranged at an image forming side, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens, an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens, and the rear side lens group including at least one anamorphic surface;
• a light receiving element array configured to photo-electrically convert the image information of the image of the original document formed thereupon by the image forming lens into the electrical signals;
• an illumination device configured to illuminate the original document;
• a scanning device configured to scan the original document;
• a signal processing device configured to process the electrical signals obtained from the light receiving element array by scanning of the original document with the scanning device;
• and
• an image processing device configured to apply image processing to the signals processed by the signal processing device.

An image forming apparatus, comprising:

• an image forming lens configured to form an image of an original document, the image forming lens including a front side lens group having 2 or more lenses and arranged at an object side, said 2 or more lenses including at least one positive lens, and a rear side lens group constituted of one negative lens and arranged at an image forming side, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens, an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens, and the rear side lens group including at least one anamorphic surface;
• a light receiving element array configured to photo-electrically convert image information of the image of the original document formed thereupon by the image forming lens into electrical signals;
• an illumination device configured to illuminate the original document;
• a scanning device configured to scan the original document;
• a signal processing device configured to process the signals obtained from the light receiving element array by scanning of the original document with the scanning device;
• an image processing device configured to process the signals processed by the signal processing device;
• and
• an image outputting device configured to form and output the image of the original document according to the signals processed by the image processing device.

An original document reading apparatus, comprising:

• means for scanning an original document;
• means for converting image information of an image of the original document formed thereupon into electrical signals;
• an image forming lens configured to image a light flux from the image of the original document being scanned by the scanning device onto the converting means, the image forming lens including a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens, and a rear side lens group constituted of one negative lens and arranged at an image forming side, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens;
• means for signal-processing the electrical signals of the converting means;
• and
• means for applying image processing to the electrical signals processed by the signal-processing means.

An image information processing apparatus, comprising:

• an original document reading device configured to form an image of an original document and to convert image information of the image of the original document into electrical signals, the original document reading device including;
• means for scanning the original document,
• means for converting the image information of the image of the original document into the electrical signals;
• an image forming lens configured to image a light flux from the image of the original document being scanned by the scanning means onto the converting means, the image forming lens including a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens, and a rear side lens group constituted of one negative lens and arranged at an image forming side, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens, and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens,
• means for signal-processing an output signal of the converting means, and
• means for applying image processing to the signal processed by the signal-processing means;
• and
• means for outputting the electrical signals of the original document reading device.

An original document reading apparatus for reading an image of an original document, comprising:

• an image forming lens configured to form the image of the original document, the image forming lens including a front side lens group having 2 or more lenses and arranged at an object side, said 2 more lenses including at least one positive lens, and a rear side lens group constituted of one negative lens and arranged at an image forming side, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens, an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens, and the rear side lens group including at least one anamorphic surface;
• means for converting image information of the image of the original document formed by the image forming lens into electrical signals;
• means for illuminating the original document;
• means for scanning the original document;
• means for signal-processing signals obtained from the converting means by scanning of the original document with the scanning means;
• and
• means for applying image processing to the signals processed by the signal-processing means.

An image forming apparatus, comprising:

• an image forming lens for forming an image of an original document, the image forming lens including a front side lens group having 2 or more lenses and arranged at an object side, said 2 or more lenses including at least one positive lens, and
• a rear side lens group constituted of one negative lens and arranged at an image forming side, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens, an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens, and the rear side lens group including at least one anamorphic surface;
• means for converting image information of the image of the original document formed by the image forming lens into electrical signals;
• means for illuminating the original document;
• means for scanning the original document;
• means for signal-processing signals obtained from the converting means by scanning of the original document;
• means for applying image processing to the signals processed by the signal processing means;
• and
• means for forming and outputting the image of the original document according to the signals processed by the image processing means.

A method of reading an image of an original document, comprising the steps of:

• providing an image forming lens comprising a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens, and a rear side lens group constituted of one negative lens and arranged at an image forming side, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens, and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens;
• scanning the original document and forming the image of the original document on a light receiving element array by the image forming lens;
• and
• converting image information of the image of the original document formed on the light receiving element array by the image forming lens to electrical signals with the light receiving element array.

A method of reading an image of an original document, comprising the steps of:

• providing an image forming lens comprising a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens, and a rear side lens group constituted of one negative lens and arranged at an image forming side, an outer shape of the rear side lens group having a rotational asymmetry with respect to an optical axis of the image forming lens, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens, and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens;
• scanning the original document and forming the image of the original document on a light receiving element array by the image forming lens;
• and
• converting image information of the image of the original document formed on the light receiving element array by the image forming lens to electrical signals with the light receiving element array.

A method of reading an image of an original document, comprising the steps of:

• providing an image forming lens comprising a front side lens group having 2 to 4 pieces of lenses and arranged at an object side, said 2 to 4 pieces of lenses including at least one positive lens, and a rear side lens group constituted of one negative lens and arranged at an image forming side, a back-focus of the image forming lens in an actual usage state thereof being equal to or smaller than 25% of an entire length of the image forming lens, and an air space between the front side lens group and the rear side lens group being equal to or greater than 50% of the entire length of the image forming lens;
• and
• scanning the original document and forming the image of the original document on a light receiving element array by the image forming lens, and
• converting image information of the image of the original document formed on the light receiving element array by the image forming lens to electrical signals with the light receiving element array, and
• integrating the rear side lens group of the image forming lens and the light receiving element array with each other so that the image forming lens and the light receiving element array forms an original document reading module.