Newton's ring apparatus

For generating Newton's rings by means of interference, a
plano-convex lens mounted together with a glass plate in a
metal frame embedded in a plastic mount on a support,
angle of wedge may be varied by means of three knurled-head
screws
Lens diameter: 55 mm
Support: L=90 mm, D=10 mm
Frame diameter: 120 mm
Distance from centre of frame to support end: 150 mm