A liquid immersion optical system includes a first optically transparent
member and a second optically transparent member, arranged in an optical
path between the first optically transparent member and an object. A
first space between the first optically transparent member and the second
optically transparent member is fillable with a first liquid. A second
space between the second optically transparent member and the object is
fillable with a second liquid. The second optically transparent member is
detachably arranged in the optical path between the first optically
transparent member and the object.