Patent ID: 6865021

Claim:
An incident illumination unit for detachable insertion into a slot part of an incident illumination device, said illumination unit comprising: an outer frame having a slot-shape which is positioned in the slot part; a centering frame which is adjustably positioned within the outer frame in a plane perpendicular to an incident illumination axis; an insertion and withdrawal part provided inside the centering frame so as to be movable onto and off from the incident illumination axis; an optical element holding part held in the insertion and withdrawal part so as to be movable along the incident illumination axis within the insertion and withdrawal part when the insertion and withdrawal part is positioned on the incident illumination axis; and an optical element which is detachably held in the optical element holding part; wherein at least one of a field stop unit and an aperture stop unit is also detachably insertable in the slot part of the incident illumination device in place of the incident illumination device.