Patent ID: 8422129

Claim:
An observation apparatus comprising: an observation optical system; a first member configured to support a first optical element constituting a part of the observation optical system; a second member configured to support a second optical element constituting another part of the observation optical system and to support the first member via a plurality of balls so as to be movable in an optical axis direction of the first optical element; and a biasing device configured to generate a biasing force for clamping the plurality of balls between the first member and the second member, wherein the plurality of balls include two first balls disposed at positions away from each other in the optical axis direction and a second ball disposed away from the two first balls in a direction orthogonal to the optical axis direction, wherein the first and second members include two guide portions which are configured to engage with corresponding one of the two first balls so as to permit a rolling motion of the two first balls in the optical axis direction and prevent a displacement of the first member with respect to the second member in the direction orthogonal to the optical axis direction, and a ball holding portion which is configured to hold the second ball so as to permit a rolling motion of the second ball in the optical axis direction, wherein the two guide portions are configured by grooves which are provided in the first and second members and extend in an optical axis direction, and widths of the grooves in a direction orthogonal to the optical axis direction are shorter than a diameter of the first ball, and wherein the ball holding portion includes a groove portion which is provided in one of the first and second members and extends in the optical axis direction, and a plane portion which is provided in the other and has a width greater than a diameter of the second ball in a direction orthogonal to the optical axis direction.