A high definition light-scanning optical apparatus uses an oblique incidence
optical
system and has a simple configuration that does not exert any adverse effect on
the quality of the image formed by it as the elements of the apparatus are appropriately
arranged. The light-scanning optical apparatus comprises an incidence optical system
adapted to cause the light beam emitted from an incident light emitting light source
including a fold mirror to strike a deflection plane of an optical deflector with
a predetermined angle in the sub-scanning section and a focussing optical system
for focussing the light beam reflected by the deflection plane of the optical deflector
on a surface to be scanned. The focussing optical system includes an f lens
system having a spherical lens and a first cylindrical lens showing power in the
main-scanning direction and a second cylindrical lens showing power in the sub-scanning direction.
