Existing variable axis lens (VAL) concepts are based upon the power series expansion of the lens field, which theoretically limits them to situations where the focusing and in-lens deflection fields are of the same type, usually magnetic. In this article, a general VAL condition is derived from the paraxial trajectory equation that is applicable to any combined focusing and in-lens deflection system with mixed magnetic and electrostatic fields. Two basic configurations of mixed-field VALs are predicated. The feasibility of a magnetic VAL using in-lens electrostatic deflectors for e-beam lithography applications is analyzed. Deflection aberration simulations show that this mixed-field VAL is comparable to its pure-field counterpart.