Mirror device comprising micromirrors possessing a specific natural oscillation frequency

A projection apparatus, comprising:

• a light source;
• a light source control circuit for controlling the light source;
• an illumination optical system for condensing the light emitted from the light source into a mirror device;
• and
• a control circuit for controlling the mirror device on the basis of an input signal, wherein the mirror device comprises a plurality of deflectable mirrors, and an elastic member for deflectably supporting the mirror, wherein the mirror allows to be controlled under a first deflection control state in which incident light is reflected toward a first direction, a second deflection control state in which the incident light is reflected toward a second direction, and a third deflection control state in which the mirror oscillates between the first deflection control state and second deflection control state, wherein the mirror device reproduces gradations by combining the first through third deflection control states, and the natural oscillation cycle T of the oscillation system constituted by the mirror and elastic member satisfies:
• 110 [μsec]>T=2π*√(I/K)>2 [μsec],
• where “I” is the moment of rotation of the oscillation system and “K” is the spring constant of the elastic member.