Circular disk in mount

For demonstrating the different focal lengths of lenses for off-axis and near-axis rays (spherical lens errors);
Frame made of black plastic; D=52 mm; with ring or pinhole diaphragm;
Acrylic glass plate with printed circular disk in mount, attachable to lens holder and aperture holder
Material: Polyamide glass fiber reinforced, black
Diameter of the circular disk: 35 mm
Dimensions: D=53 mm, H=26 mm
Mass: approx. 15 g