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.
1. A viewing device comprising:
an eyepiece; and
a reference plate that is provided with a first clear plate including a reticle forming surface on which a reticle is formed, said reference plate being positioned on an optical axis of said eyepiece, and further provided with a second clear plate including a frame forming surface on which a frame for a field of view is formed;
wherein said reticle forming surface is curved in accordance with a field curvature of said eyepiece,
wherein said reticle forming surface and said frame forming surface are arranged so as to face each other, and
wherein the radius of curvature of said reticle forming surface and the radius of curvature of said frame forming surface are different.
2. A viewing device according to claim 1 , wherein said reticle forming surface is curved so as to approximately accord with a field curvature of a sagittal image surface of said eyepiece.
3. A viewing device according to claim 1 , wherein said first and second clear plates are bonded in such a manner that said reticle forming surface is a bonded surface.
4. A viewing device according to claim 3 , wherein, on said reference plate, both an incidence surface and an exit surface are planar.
5. A viewing device according to claim 1 , wherein said reference plate has no significant refracting power.
6. A viewing device according to claim 1 , wherein said frame forming surface is curved so as to approximately accord with a field curvature of a meridional image surface of said eyepiece.
7. A viewing device according to claim 1 , further comprising a sealing member that hermetically seals a gap which is formed between the peripheral portions of said first and second clear plates.