It's called a reseau grid. The crosses are used as a reference points for measuring distances between objects in the image. They can also be used to correct di

It's called a reseau grid. The crosses are used as a reference points for measuring distances between objects in the image. They can also be used to correct distortions after development or scanning.. This page talks about it in detail. http://www.clavius.org/photoret.html http://www.clavius.org/photoret.html