Observation optical system

An observation optical system which forms an exit pupil for observation of an electronic image displayed on an image display element and which has a positive refracting power as a whole, comprising:

• a first unit having a positive refracting power;
• and
• a second unit;
• wherein said first unit comprises at least one prism member having a positive refracting power;
• and
• said second unit comprises a diffraction element having a lens function caused by diffraction,
• wherein said first unit has an action of imaging the electronic image for obtaining a relay image,
• said second unit has an action for forming the exit pupil for introducing the relay image into an observer,
• said prism member has:
• an entrance surface via which bundles of rays emergent from the image display element enter said prism member;
• at least one reflecting surface on which the bundles of rays reflect inside said prism member;
• and
• an exit surface via which the bundles of rays exit out of said prism member;
• at least one of said reflecting surface and said exit surface is shaped as a curved surface which exerts a power on the bundles of rays, said curved surface being a rotationally asymmetric surface constructed and arranged to compensate aberrations caused by decentering, and
• wherein said second unit exerts no power on bundles of rays transmitted therethrough.

An observation optical system which forms an exit pupil for observation of an electronic image displayed on an image display element and which has a positive refracting power as a whole, comprising:

• a first unit having a positive refracting power;
• and
• a second unit;
• wherein said first unit comprises at least one prism member having a positive refracting power;
• and
• said second unit comprises a diffraction element having a lens function caused by diffraction,
• wherein said first unit has an action of imaging the electronic image for obtaining a relay image,
• said second unit has an action for forming the exit pupil for introducing the relay image into an observer,
• said prism member has:
• an entrance surface via which bundles of rays emergent from the image display element enter said prism member;
• at least one reflecting surface on which the bundles of rays reflect inside said prism member;
• and
• an exit surface via which the bundles of rays exit out of said prism member;
• at least one of said reflecting surface and said exit surface is shaped as a curved surface which exerts a power on the bundles of rays, said curved surface being a rotationally asymmetric surface constructed and arranged to compensate aberrations caused by decentering, and
• wherein said first unit comprises a diffraction element.