A reference plate is situated on an optical axis of an eyepiece. The reference
plate includes a first glass plate and a second glass plate. One surface of the
first glass plate and one surface of the second glass plate are bonded. Cross hairs
are formed on the bonded surface of the first glass plate by using a chromium plating
and so on. A radius of curvature of the bonded surface accords with the field curvature
of the sagittal image surface of the eyepiece.
