Prism unit and projector

A projector comprising:

• an illumination unit that generates incident illumination light;
• a prism unit that guides the illumination light to a reflective image display device to illuminate the reflective image display device, guides projection light, which is reflected by the reflective image display device, to an externally provided projection lens, and allows the projection light to exit the prism unit, wherein the prism unit comprises:
• a first prism comprising:
• a first optical surface that allows the illumination light to enter the first prism,
• a second optical surface that reflects the illumination light—that entered through the first optical surface, and
• a third optical surface that allows the illumination light reflected by the second optical surface to exit the first prism;
• a reflecting means that reflects the illumination light that has exited the third optical surface with an angular difference so that the illumination light enters the third optical surface and is transmitted through the second optical surface to exit the first prism;
• a second prism comprising:
• a fourth optical surface that:
• forms a first air gap with the second optical surface, and
• allows the illumination light that exited through the second optical surface to enter the second prism, and
• a fifth optical surface that allows the illumination light that entered through the fourth optical surface to exit the second prism;
• and
• a third prism comprising:
• a sixth optical surface that:
• forms a second air gap with the fifth optical surface, and
• allows the illumination light that exited through the fifth optical surface to enter the third prism,
• a seventh optical surface that allows the illumination light that entered through the sixth optical surface to exit the third prism, and
• an eighth optical surface that allows projection light to exit the third prism;
• and
• the reflective image display device disposed outside of and opposite to the seventh optical surface of the third prism unit, wherein
• the projection light is the illumination light that exits through the seventh optical surface, incident on and reflected by the reflective image display device, enters the third prism through the seventh optical surface, and is reflected by the sixth optical surface, and
• a relationship of |P6−L1|≤|P6−L6| is satisfied, where:
• L1 is a distance between an intersection of a principal ray of the illumination light and the first optical surface and a surface of the reflective image display device,
• L6 is a distance between an intersection of the principal ray of the illumination light and the sixth optical surface and the surface of the reflective image display device, and
• P6 is a distance between an intersection of a principal ray of the projection light reflected by the reflective image display device and the sixth optical surface and the surface of the reflective image display device.

A prism unit that guides incident illumination light to a reflective image display device to illuminate the reflective image display device, guides projection light, which is reflected by the reflective image display device, to an externally provided projection lens, and allows the projection light to exit the prism unit, the prism unit comprising:

• a first prism comprising:
• a first optical surface that allows the illumination light to enter the first prism,
• a second optical surface that reflects the illumination light—that entered through the first optical surface, and
• a third optical surface that allows the illumination light reflected by the second optical surface to exit the first prism;
• a reflecting means that reflects the illumination light that has exited the third optical surface with an angular difference so that the illumination light enters the third optical surface and is transmitted through the second optical surface to exit the first prism;
• a second prism comprising:
• a fourth optical surface that:
• forms a first air gap with the second optical surface, and
• allows the illumination light that exited through the second optical surface to enter the second prism, and
• a fifth optical surface that allows the illumination light that entered through the fourth optical surface to exit the second prism;
• and
• a third prism comprising:
• a sixth optical surface that:
• forms a second air gap with the fifth optical surface, and
• allows the illumination light that exited through the fifth optical surface to enter the third prism,
• a seventh optical surface that connects the sixth optical surface to an eighth optical surface, and
• the eighth optical surface that allows the illumination light that entered through the sixth optical surface to exit the third prism;
• and
• a fourth prism comprising:
• a ninth optical surface that allows the illumination light that exited the eighth surface to enter the fourth prism;
• and
• a surface perpendicular to a tenth optical surface that allows the illumination light that entered through the ninth optical surface to exit the fourth prism, and
• wherein the projection light is the illumination light that exits through the surface perpendicular to the tenth optical surface, incident on and reflected by the reflective image display device, enters the fourth prism through the surface perpendicular to the tenth optical surface, and is reflected by the sixth optical surface.