Electrically controlled optical elements and method

A method for electrically controlling the effective focal length of a light path of an optical system comprising the steps:

• polarizing light input into light path into a first polarization orientation;
• passing the light with the first polarization orientation or changing the light into polarized light of a second orientation under control of control electronics;
• passing the light with the first or second polarization orientation through a half-silvered mirror;
• in a polarization dependent mirror, passing light with a first polarization orientation and reflecting light with a second polarization orientation from the half-silvered mirror;
• in the half-silvered mirror, reflecting the light with the second polarization orientation from the polarization dependent mirror while transforming the light with the second polarization orientation into light with a first polarization orientation;
• and
• passing the light with the first polarization orientation through the polarization dependent mirror.