Any ideas what this might be? There is a rectangular lens with "crosshairs" set in a metal frame. The lens frame is hinged to lay flat or rotate at 90 degrees. The lens is about 7/8" x 1-1/8" with an overall size of 1-1/4" x 1-1/4". No markings of any kind. I THINK it may be some type of focus finder but any ideas you may have would be helpful. Thank you!
