Irisl diaphragm in mount

For demonstrating the different focal lengths of lenses for off-axis and near-axis rays (spherical lens errors);
Ring diaphragm (pinhole diaphragm) in mount, attachable to lens holder and diaphragm holder
Material: Polyamide glass fiber reinforced, black
Hole diameter of the aperture: 20 mm
Dimensions: D=53 mm, H=26 mm
Mass: approx. 14 g