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An aspheric reduction objective has a catadioptric partial objective (L1), an intermediate image (IMI) and a refractive partial objective (L2). The catadioptric partial objective has an assembly centered to the optical axis and this assembly includes two mutually facing concave mirrors (M1, M2). The

An aspheric reduction objective has a catadioptric partial objective (L1), an intermediate image (IMI) and a refractive partial objective (L2). The catadioptric partial objective has an assembly centered to the optical axis and this assembly includes two mutually facing concave mirrors (M1, M2). The cutouts in the mirrors (B1, B2) lead to an aperture obscuration which can be held to be very small by utilizing lenses close to the mirrors and having a high negative refractive power and aspheric lens surfaces (27, 33). The position of the entry and exit pupils can be corrected with aspherical lens surfaces (12, 48, 53) in the field lens groups. The number of spherical lenses in the refractive partial objective can be reduced with aspherical lens surfaces (66, 78) arranged symmetrically to the diaphragm plane. Neighboring aspheric lens surfaces (172, 173) form additional correction possibilities.

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An aspheric reduction objective has a catadioptric partial objective (L1), an intermediate image (IMI) and a refractive partial objective (L2). The catadioptric partial objective has an assembly centered to the optical axis and this assembly includes two mutually facing concave mirrors (M1, M2). The

An aspheric reduction objective has a catadioptric partial objective (L1), an intermediate image (IMI) and a refractive partial objective (L2). The catadioptric partial objective has an assembly centered to the optical axis and this assembly includes two mutually facing concave mirrors (M1, M2). The cutouts in the mirrors (B1, B2) lead to an aperture obscuration which can be held to be very small by utilizing lenses close to the mirrors and having a high negative refractive power and aspheric lens surfaces (27, 33). The position of the entry and exit pupils can be corrected with aspherical lens surfaces (12, 48, 53) in the field lens groups. The number of spherical lenses in the refractive partial objective can be reduced with aspherical lens surfaces (66, 78) arranged symmetrically to the diaphragm plane. Neighboring aspheric lens surfaces (172, 173) form additional correction possibilities. er. No. 10/028,418, filed Dec. 19, 2001 entitled "Renewable Liquid Reflecting Zone Plate" are incorporated herein by this reference. of channels greater than the predetermined number. 3. An apparatus as in claim 1, wherein, when the number of channels in the optical signal is less than the predetermined number, the controller controls the first pump light source to provide pump light to the optical amplification medium at a power level appropriate to amplify the optical signal based on the number of channels in the optical signal. 4. An apparatus as in claim 1, wherein, when the number of channels in the optical signal is at a first number less than the predetermined number, the controller controls the first pump light source to provide pump light power at a power level appropriate to amplify the optical signal having the first number of channels, and when the number of channels in the optical signal is increased from the first number to a higher number less than the predetermined number of channels, the controller controls the first pump light source to increase the power level of the pump light provided to the optical amplification medium to a pump power appropriate to amplify the optical signal having the higher number of channels. 5. An apparatus as in claim 3, wherein, when the first pump light source is providing pump light to the optical amplification medium to amplify an optical signal having a number of channels less than or equal to the predetermined number, and the number of channels in the optical signal is thereafter increased to a higher number than the predetermined number of channels, the controller controls the second pump light source to provide pump light at a constant power level after the number of channels is increased from the predetermined number to the higher number. 6. An apparatus as in claim 4, wherein, when the first pump light source is providing pump light to the optical amplification medium to amplify an optical signal having a number of channels less than or equal to the predetermined number, and the number of channels in the optical signal is thereafter increased to a higher number than the predetermined number of channels, the controller controls the second pump light source to provide pump light at a constant power level after the number of channels is increased from the predetermined number to the higher number. 7. An apparatus as in claim 1, wherein, when the first pump light source is providing pump light to the optical amplification medium to amplify an optical signal having a number of channels less than or equal to the predetermined number, and the number of channels in the optical signal is thereafter increased to a higher number than the predetermined number of channels, the controller controls the second pump light source to provide pump light at a constant power level after the number of channels is increased from the predetermined number to the higher number, and controls the first pump light source to provide pump light at an appropriate power level so that the total pump light provided the first and second pump lights is appropriate to amplify the optical signal having the higher number of channels. 8. An apparatus as in claim 4, wherein, when the first pump light source is providing pump light to the optical amplification medium to amplify an optical signal having a number of channels less than or equal to the predetermined number, and the number of channels in the optical signal is thereafter increased to a higher number than the predetermined number of channels, the controller controls the second pump light source to provide pump light at a constant power level after the number of channels is increased from the predetermined number to the higher number, and controls the first pump light source to provide pump light at an appropriate power level so that the total pump light provided the first and second pump lights is appropriate to amplify the optical signal having the higher number of channels. 9. An apparatus as in claim 5, wherein, when the first pump light source is providing pump lig ht to the optical amplification medium to amplify an optical signal having a number of channels less than or equal to the predetermined number, and the number of channels in the optical signal is thereafter increased to a higher number than the predetermined number of channels, the controller controls the second pump light source to provide pump light at a constant power level after the number of channels is increased from the predetermined number to the higher number, and controls the first pump light source to provide pump light at an appropriate power level so that the total pump light provided the first and second pump lights is appropriate to amplify the optical signal having the higher number of channels. 10. An apparatus as in claim 6, wherein, when the first pump light source is providing pump light to the optical amplification medium to amplify an optical signal having a number of channels less than or equal to the predetermined number, and the number of channels in the optical signal is thereafter increased to a higher number than the predetermined number of channels, the controller controls the second pump light source to provide pump light at a constant power level after the number of channels is increased from the predetermined number to the higher number, and controls the first pump light source to provide pump light at an appropriate power level so that the total pump light provided the first and second pump lights is appropriate to amplify the optical signal having the higher number of channels. 11. An apparatus as in claim 1, wherein, when the first pump light source is providing pump light to the optical amplification medium to amplify an optical signal having a number of channels less than or equal to the predetermined number, and the number of channels in the optical signal is thereafter increased to higher numbers than the predetermined number of channels, the controller controls the second pump light source to provide pump light at a constant power level after the number of channels is increased from the predetermined number to the higher numbers, and controls the first pump light source to provide pump light at an appropriate power level so that the total pump light provided the first and second pump lights is appropriate to amplify the optical signal having the higher numbers of channels. 12. An apparatus for amplifying an optical signal having a variable number of channels associated with different wavelengths, comprising: an optical amplification medium through which the optical signal travels; first and second pump light sources; and means for controlling the first and second pump light sources so that, when the number of channels in the optical signal is less than or equal to a predetermined number, the first pump light source, but not the second pump light source, provides pump light to the optical amplification medium so that the optical signal is amplified as the optical signal travels through the optical amplification medium, and when the first pump light source is providing pump light to the optical amplification medium to amplify an optical signal having a number of channels less than or equal to the predetermined number, and the number of channels in the optical signal is thereafter increased to a number greater than the predetermined number of channels, a power level of the pump light provided to the optical amplification medium by the first pump light source is reduced, and the second pump light source provides pump light to the optical amplification medium to amplify the optical signal as the optical signal travels through the optical amplification medium. 13. A method for amplifying an optical signal having a variable number of channels associated with different wavelengths, comprising: causing the optical signal to travel through an optical amplification medium; providing first and second pump light sources; and controlling the first and second pump ligh t sources so that, when the number of channels in an optical signal is less than or equal to a predetermined number, the first pump light source, but not the second pump light source, provides pump light to the optical amplification medium so that the optical signal is amplified as the optical signal travels through the optical amplification medium, and when the first pump light source is providing pump light to the optical amplification medium to amplify an optical signal having a number of channels less than or equal to the predetermined number, and the number of channels in the optical signal is thereafter increased to a number greater than the predetermined number of channels, a power level of the pump light provided to the optical amplification medium by the first pump light source is reduced, and the second pump light source provides pump light to the optical amplification medium to amplify the optical signal as the optical signal travels through the optical amplification medium. 14. An apparatus for amplifying an optical signal having a variable number of channels associated with different wavelengths, comprising: an optical amplification medium through which the optical signal travels; first and second pump light sources; and a controller controlling the first and second pump light sources so that, when the number of channels in the optical signal is less than or equal to a predetermined number, the first pump light source, but not the second pump light source, provides pump light to the optical amplification medium so that the optical signal is amplified as the optical signal travels through the optical amplification medium, and when the first pump light source is providing pump light to the optical amplification medium to amplify an optical signal having a number of channels less than or equal to the predetermined number, and the number of channels in the optical signal is thereafter increased to higher numbers than the predetermined number of channels, a transition period occurs in which the first pump light source provides pump light at a reduced power level and the second pump light source provides pump light at an increasing rate and, after the transition period, the second pump light source provides pump light at a constant power level and the first pump light source provides pump light at an appropriate power level so that the total pump light provided the first and second pump lights is appropriate to amplify the optical signal having the higher numbers of channels. 15. An apparatus for amplifying an optical signal having a variable number of channels associated with different wavelengths, comprising: an optical amplification medium through which the optical signal travels; first and second pump light sources; and means for controlling the first and second pump light sources so that, when the number of channels in the optical signal is less than or equal to a predetermined number, the first pump light source, but not the second pump light source, provides pump light to the optical amplification medium so that the optical signal is amplified as the optical signal travels through the optical amplification medium, and when the first pump light source is providing pump light to the optical amplification medium to amplify an optical signal having a number of channels less than or equal to the predetermined number, and the number of channels in the optical signal is thereafter increased to higher numbers than the predetermined number of channels, a transition period occurs in which the first pump light source provides pump light at a reduced power level and the second pump light source provides pump light at an increasing rate and, after the transition period, the second pump light source provides pump light at a constant power level and the first pump light source provides pump light at an appropriate power level so that the total pump light provided the first and second pump lights is appr