An observation apparatus is provided. An apex angle of a contact prism is
inputted by operating an apex angle setting knob of a control panel. A
fining angle of the contact prism is inputted by operating a fitting
angle setting knob. A control unit determines the amount of correction
for astigmatism of a left observation optical system and the amount of
correction for astigmatism of a right observation optical system based on
a recognized observation magnification and the inputted apex angle. An
axial angle for the astigmatism of the left observation optical system
and an axial angle for the astigmatism of the right observation optical
system are determined based on the inputted fitting angle. Variable cross
cylinder lens rotating drive units are controlled to rotate cylinder
lenses of each of the right and left observation optical systems, thereby
obtaining the determined axial angle and the determined amount of
correction.