Observation optical system using volume hologram

An image observation optical system comprising:

• an image display element;
• and
• an eyepiece optical system which introduces an image displayed on said image display element to an observer side without forming an intermediate image, so as to allow an observer to observe said image as a virtual image,
• wherein said eyepiece optical system is constructed and arranged to bend an optical axis using reflecting surfaces so as to be compact, said optical axis lying in a plane,
• wherein said eyepiece optical system is symmetrically formed with respect to said plane and includes an optical element having an entrance surface, a plurality of curved reflecting surfaces and an exit surface, at least one of said reflecting surfaces being provided with a volume hologram (HOE), and
• wherein said eyepiece optical system comprises a prism with a positive refracting power, and, upon an image position F0 at a midpoint, an image position Fb at one end point showing a larger chromatic aberration of magnification, and an image position Fa at another end point showing a smaller chromatic aberration of magnification being defined on a segment that is an intersection formed by said plane of symmetry of said eyepiece optical system and an image display surface, said image observation optical system satisfies the following conditions simultaneously:
• −1<φy(HOE, Fa)/φy(Total)<2
• −1<φy(HOE, Fb)/φy(Total)<1
• where φy (HOE, Fa) is a y-direction power of said HOE at the image position Fa, φy (HOE, Fb) is a y-direction power of said HOE at the image position Fb, and φy (Total) is a y-direction power of an entire system.