Step 7 of 8: Find the material to next surface

This is easy.

The tricky part is that the material for each surface comes after the surface. Thus, in our case, the material for the OBJ surface is just air.

The material for the next surface (the AST surface) is the glass that the lens is made from

The material for the next surface is air again!

Once again, you don't have to worry about the last surface and can leave it as air.

So, the table describing your optical system is

Surface	Curvature	Distance	Height	Material
OBJ	0	Dobj	hobj	air
AST	Rast	Dast	hast	glass
2	R2	D2	h2	air
IMS	0	(calc)	(calc)	air