Optical device and single lens reflex camera

An optical device for forming an image of an object, comprising:

• a semitransparent mirror surface disposed on an optical path along which light of the image of the object proceeds;
• and
• a light projection unit configured to project light to the semitransparent mirror surface and thereby to combine, on the optical path, the light projected by the light projection unit and reflecting from the semitransparent mirror surface with the image of the object transmitting through the semitransparent mirror surface,
• wherein;
• a first wavelength region is defined in a visible light region to include a wavelength of the light projected by the light projection unit;
• the semitransparent mirror surface has a substantially flat transmissivity property within a second wavelength region which is defined in the visible light region not to include the first wavelength region;
• and
• reflectance of the semitransparent mirror surface at the wavelength of the light projected by the light projection unit is higher by 10% to 50% than reflectance in the second wavelength region;
• and
• wherein the semitransparent mirror surface has a reflectance property in the first wavelength region with a peak, such that a reflectance of the semitransparent mirror surface for the light projected by the light projection unit becomes higher locally at a wavelength corresponding to the peak.

A single lens reflex camera, comprising:

• an objective optical system;
• and
• a finder device;
• wherein the finder device comprises:
• a semitransparent mirror surface disposed on an optical path along which light of an image of an object proceeds;
• and
• a light projection unit configured to project light to the semitransparent mirror surface and thereby to combine, on the optical path, the light projected by the light projection unit and transmitting through the semitransparent mirror surface with the image of the object reflecting from the semitransparent mirror surface;
• wherein:
• a first wavelength region is defined in a visible light region to include a wavelength of the light projected by the light projection unit;
• the semitransparent mirror surface has a substantially flat reflectance property within a second wavelength region which is defined in the visible light region not to include the first wavelength region;
• and
• transmissivity of the semitransparent mirror surface at the wavelength of the light projected by the light projection unit is higher by 10% to 50% than transmissivity in the second wavelength region;
• and
• wherein the semitransparent mirror surface has a reflectance property in the first wavelength region with a valley, such that a transmissivity of the semitransparent mirror surface for the light projected by the light projection unit becomes higher locally at a wavelength corresponding to the valley.

A single lens reflex camera, comprising:

• an objective optical system;
• and
• a finder device;
• wherein the finder device comprises:
• a semitransparent mirror surface disposed on an optical path along which light of an image of an object proceeds;
• and
• a light projection unit configured to project light to the semitransparent mirror surface and thereby to combine, on the optical path, the light projected by the light projection unit and reflecting from the semitransparent mirror surface with the image of the object transmitting through the semitransparent mirror surface;
• wherein:
• a first wavelength region is defined in a visible light region to include a wavelength of the light projected by the light projection unit;
• the semitransparent mirror surface has a substantially flat transmissivity property within a second wavelength region which is defined in the visible light region not to include the first wavelength region;
• and
• reflectance of the semitransparent mirror surface at the wavelength of the light projected by the light projection unit is higher by 10% to 50% than reflectance in the second wavelength region;
• and
• wherein the semitransparent mirror surface has a reflectance property in the first wavelength region with a peak, such that a reflectance of the semitransparent mirror surface for the light projected by the light projection unit becomes higher locally at a wavelength corresponding to the peak.