It is therefore a " skew " plane, in other words not a meridional plane.
2.
Such a plane is called a " meridional plane "; it is a cross-section through the system.
3.
This plane is called either the " sagittal meridional plane " or, confusingly, just the " sagittal plane ".
4.
In the analysis of these systems, it is common to consider tangential rays ( as defined above ), and rays in a meridional plane ( a plane containing the optic axis ) perpendicular to the tangential plane.
मोबाइल