Optical scanning apparatus and image forming apparatus employing this apparatus

An optical scanning apparatus comprising:

• a light source;
• a deflection unit configured to deflect a light flux emitted by the light source;
• a first optical system configured to condense, at the deflection unit, a divergent light flux emitted by the light source;
• a second optical system configured to focus, on a target scanning face, the light flux deflected by the deflection unit,
• wherein the wavelength of the light flux emitted by the light source is 450 nm or shorter, and
• a first refractive optical element made of plastic is arranged in the second optical system, and a first diffractive optical element having a diffraction surface is arranged in the first optical system, and
• power for the first refractive optical element in a main scanning direction and power for the diffraction surface of the first diffractive optical element in the main scanning direction have the same sign, and
• a second diffractive optical element having a diffraction surface is located in the second optical system;
• and wherein the same sign is employed for the power at the diffraction surface of the second diffractive optical element in the main scanning direction and the power at the first refractive optical element in the main scanning direction.

An optical scanning apparatus comprising:

• a light source;
• a deflection unit configured to deflect a light flux emitted by the light source;
• a first optical system configured to condense, at the deflection unit, a divergent light flux emitted by the light source;
• a second optical system configured to focus, on a target scanning face, the light flux deflected by the deflection unit,
• wherein the wavelength of the light flux emitted by the light source is 450 nm or shorter and
• a first refractive optical element made of plastic is arranged in the second optical system, and a first diffractive optical element having a diffraction surface is arranged in the first optical system, and
• power for the first refractive optical element in a main scanning direction and power for the diffraction surface of the first diffractive optical element in the main scanning direction have the same sign, and
• a temperature characteristic of the wavelength of the light flux emitted by the light source is 0.03 (nm/° C.)<dλ/dt<0.10 (nm/° C.).

An optical scanning apparatus comprising:

• a light source;
• a deflection unit, configured to deflect a light flux emitted by the light source;
• a first optical system, which includes a second refractive optical element that includes at the least one lens that condenses, toward the deflection unit, divergent light flux emitted by the light source;
• and
• a second optical system, which includes a first refractive optical element made of plastic configured to focus, on a target scanning face, a light flux deflected by the deflection unit,
• wherein a wavelength of a light flux emitted by the light source is equal to or shorter than 450 nm,
• wherein a first diffractive optical element having a diffraction surface is located in the first optical system,
• wherein power for the first refractive optical element in a main scanning direction and power for the diffraction surface of the first diffractive optical element in the main scanning direction have the same sign,
• wherein, when synthesis power in a main scanning direction for the first optical system is denoted by φ, and power in a main scanning direction for an i-th lens that constitutes the second refractive optical element is denoted by φi, the refractive index of the i-th lens that constitutes the second refractive optical element is denoted by ni, a refractive index wavelength change rate for the i-th lens that constitutes the second refractive optical element is denoted by dni/dλ, the power for the diffraction surface of the first diffractive optical element in the main scanning direction is denoted by φdo, an imaging magnification of the optical scanning apparatus in the main scanning direction is denoted by β and an emission F number for the second optical system in the main scanning direction is denoted by FNo. satisfies,
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