Aperture-plate moving mechanism

An infrared microscope, comprising an aperture-plate moving mechanism including:

• a) a drive block fixed to an aperture plate;
• b) a linear motion guide for allowing the drive block to move along an axis while preventing the drive block from moving in other directions;
• c) a feed screw laid in a direction of the axis;
• d) a nut member having a threaded hole engaged with the feed screw, the nut member being prevented from rotating due to a rotation of the feed screw;
• and
• e) an urging member for pressing the drive block onto the nut member in the direction of the axis to make a contact portion of the drive block be in contact with a contact portion of the nut member,
• where:
• with respect to the direction of the axis, the contact portions of the drive block and the nut member are shaped so that one of the contact portions has a convex surface while the other contact portion is has either a flat surface or a concave surface having a larger radius of curvature than the convex surface.