Rotation Angle Detecting Apparatus And Surveying Instrument

A rotation angle detecting apparatus, comprising a bearing holder, a rotation shaft rotatably supported by said bearing holder, a shaft portion space formed in said rotation shaft, a bearing holder space formed in said bearing holder, a first condenser lens which is accommodated in said shaft portion space and has an optical axis that coincides with a center line of said rotation shaft, a second condenser lens which is provided in said bearing holder space and also provided on an extension of a center line of said rotation shaft, an angle detection pattern provided at a focal position of one of said first condenser lens and said second condenser lens, and an image sensor provided at a focal position of the other of said first condenser lens and said second condenser lens, wherein said image sensor detects a projection image of said angle detection pattern projected onto said image sensor, and a displacement of said projection image involved by the rotation of said rotation shaft is detected.