| 摘要 |
PROBLEM TO BE SOLVED: To obtain an fθlens whose shape is appropriately set so that it may be compact and suitable for high-definition printing, and a scanning optical device having the fθlens. SOLUTION: The fθlens for forming an image in a spot state on a surface to be scanned with luminous flux emitted from a light source means is constituted of at least two lens surfaces. By consecutively changing the curvature of two lens surfaces in a subscanning direction from an axial state to an off-axis state, an axial principal plane position in the subscanning direction and an off-axis principal plane position in the subscanning direction are made different in an optical axis direction so as to restrain the change of an f-number in the subscanning direction caused by the image height of the luminous flux made incident on the surface to be scanned. COPYRIGHT: (C)2004,JPO
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