Patent ID: 7706074

Claim:
A projection optical system provided with at least one of optical members made of a calcium fluoride single crystal, wherein each of the optical members satisfies at least any one of the following conditions of (i) to (iii): (i) an RMS value of a spatial frequency component having a number of periods f PD in partial diameter in a range from 10 periods to 50 periods inclusive, out of fluctuation of a transmission wavefront relative to light having a wavelength of 633 nm, is equal to or below 0.35 nm/cm; (ii) an RMS value of a spatial frequency component having a number of periods f PD in partial diameter in a range from 10 periods to 100 periods inclusive, out of fluctuation of a transmission wavefront relative to light having a wavelength of 633 nm, is equal to or below 0.45 nm/cm; and (iii) an RMS value of a spatial frequency component having a number of periods f PD in partial diameter in a range from 10 periods to 150 periods inclusive, out of fluctuation of a transmission wavefront relative to light having a wavelength of 633 nm, is equal to or below 0.50 nm/cm.