An optical system including a first optical element having a curved first major surface and an optical stack bonded and conforming to the curved first major surface of the first optical element is described. The optical stack includes a reflective polarizer substantially transmitting light having a first polarization state and substantially reflecting light having an orthogonal second polarization state and a non-adhesive flexible optical layer bonded to the reflective polarizer and comprising substantially parallel opposing first and second major surfaces. At least one location on the non-adhesive flexible optical layer has an optical retardance of less than about 100 nm or greater than about 200 nm at a wavelength of about 550 nm.