| US 7,570,444 B2 | ||
| Imaging optical system and image reading apparatus using the same | ||
| Nobuyuki Tochigi, Utsunomiya (Japan); Takeyoshi Saiga, Utsunomiya (Japan); Tadao Hayashide, Utsunomiya (Japan); and Kazuyuki Kondo, Saitama (Japan) | ||
| Assigned to Canon Kabushiki Kaisha, Tokyo (Japan) | ||
| Filed on May 30, 2008, as Appl. No. 12/129,875. | ||
| Application 12/129875 is a division of application No. 11/772457, filed on Jul. 02, 2007, granted, now 7,397,585. | ||
| Application 11/772457 is a division of application No. 11/336974, filed on Jan. 23, 2006, granted, now 7,253,928, filed on Aug. 07, 2007. | ||
| Claims priority of application No. 2005-029298 (JP), filed on Feb. 04, 2005. | ||
| Prior Publication US 2008/0239440 A1, Oct. 02, 2008 | ||
| Int. Cl. G02B 7/00 (2006.01) | ||
| U.S. Cl. 359—896 [358/483] | 6 Claims |
| 1. An imaging optical system for image reading, in which image information on a surface of an original is imaged on a line
sensor and the image information is read by the line sensor, comprising:
a first off-axial optical element and a second off-axial optical element disposed in order from an original side, each of
the first and second off-axial optical elements is a reflection type off-axial optical element having free-form surface shape
and made of a resin material,
wherein, letting a main scanning direction be a line direction of the line sensor and a sub-scanning direction be a direction
orthogonal to the main scanning direction, a length of each of the first and second off-axial optical elements in the main
scanning direction is longer than a length thereof in the sub-scanning direction and a thickness thereof is smaller than the
length thereof in the sub-scanning direction, and
wherein in a sub-scanning section in which the main scanning direction corresponds to a normal, the following condition is
satisfied,
−30 °<θa −θb<30°,
where θa represents an absolute value of a first angle formed between a surface normal to a reflective surface of the first off-axial
optical element at a reflection point of the reflective surface of the first off-axial optical element at which a reference
axis light beam is reflected and a reference axis light beam incident on the reflective surface of the first off-axial optical
element and θb represents an absolute value of a second angle formed between a surface normal to a reflective surface of the
second off-axial optical element at a reflection point of the reflective surface of the second off-axial optical element at
which the reference axis light beam is reflected and the reference axis light beam incident on the reflective surface of the
first off-axial optical element.
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