Optical system and image display apparatus

An optical system configured to guide light from a display element to an observation side, the optical system comprising:

• a first lens having a first half-transmissive reflective surface;
• and
• a second lens having a second half-transmissive reflective surface,
• wherein the light from the display element transmits through the second half-transmissive reflective surface, is reflected on the first half-transmissive reflective surface, is reflected on the second half-transmissive reflective surface, transmits through the first half-transmissive reflective surface, and is guided to the observation side,
• wherein one of the first lens, the second lens, and another lens has negative refractive power, and
• wherein the light from the display element transmits through the one having the negative refractive power only once and is guided to the observation side.

A display apparatus comprising:

• an optical system configured to guide light from a display element to an observation side;
• and
• the display element,
• wherein the optical system includes:
• a first lens having a first half-transmissive reflective surface provided to a surface on a display element side of the first lens;
• and
• a second lens having a second half-transmissive reflective surface,
• wherein the light from the display element transmits through the second half-transmissive reflective surface, is reflected on the first half-transmissive reflective surface, is reflected on the second half-transmissive reflective surface, transmits through the first half-transmissive reflective surface, and is guided to the observation side,
• wherein one of the first lens, the second lens, and another lens has negative refractive power,
• wherein the first lens has a concave surface facing the observation side, and
• wherein the following inequality is satisfied:
• 1.
• ≤
• ❘
• "\[LeftBracketingBar]"
• fn
• /
• f
• ❘
• "\[RightBracketingBar]"
• ≤
• 20.
• where fn is a focal length of the one having the negative refractive power, and f is a focal length of the optical system.

A display apparatus comprising:

• an optical system configured to guide light from a display element to an observation side;
• and
• the display element,
• wherein the optical system includes:
• a first lens having a first half-transmissive reflective surface;
• and
• a second lens having a second half-transmissive reflective surface,
• wherein the light from the display element transmits through the second half-transmissive reflective surface, is reflected on the first half-transmissive reflective surface, is reflected on the second half-transmissive reflective surface, transmits through the first half-transmissive reflective surface, and is guided to the observation side,
• wherein one of the first lens, the second lens, and another lens has negative refractive power, and
• wherein the light from the display element transmits through the one having the negative refractive power only once and is guided to the observation side.

An optical system configured to guide light from a display element to an observation side, the optical system comprising:

• a first lens having a first half-transmissive reflective surface provided to a surface on a display element side of the first lens;
• and
• a second lens having a second half-transmissive reflective surface,
• wherein the light from the display element transmits through the second half-transmissive reflective surface, is reflected on the first half-transmissive reflective surface, is reflected on the second half-transmissive reflective surface, transmits through the first half-transmissive reflective surface, and is guided to the observation side,
• wherein one of the first lens, the second lens, and another lens has negative refractive power,
• wherein the first half-transmissive reflective surface has a curved shape, and
• wherein the following inequality is satisfied:
• 1.
• ≤
• ❘
• "\[LeftBracketingBar]"
• fn
• /
• f
• ❘
• "\[RightBracketingBar]"
• ≤
• 20.
• where fn is a focal length of the one having the negative refractive power, and f is a focal length of the optical system.