Infrared continuous zoom telescope using diffractive optics

A color correcting lens system comprising:

• (a) a zoom afocal lens system including:
• (i) an objective lens;
• (ii) an eyepiece lens;
• (iii) a plurality of lenses disposed between said objective lens and said eyepiece lens;
• and
• (iv) a diffractive pattern disposed at a surface of said objective lens to provide color correction at a predetermined wavelength of light passing therethrough, said diffractive pattern comprising a plurality of spaced ring-shaped steps, each ring concentric with the center of said objective lens and each step having a height equal to said predetermined wavelength said plurality of ring-shaped steps being formed in accordance with the formula ##EQU2## where:
• Z is Sag value along the z-axis or optical axis
• Y is the semi-diameter height
• CC is the base curvature (i/radius) of the surface
• K is the conic coefficient of the surface
• A, B, C and D are the 4th, 6th, 8th and 10th order aspheric coefficients, respectively
• HOR is the diffraction order, generally 1 or -1
• .lambda. is the design wavelength for the surface
• N1 is the refractive index of the material preceding the diffractive surface
• N2 is the refractive index of the material following the diffractive surface
• C1, C2 and C3 are coefficients for describing aspheric phase departure
• INT is an integer function;
• (b) all of said lenses of said system being germanium lenses.

A color correcting objective lens comprising:

• (a) a germanium objective lens;
• and
• (d) a diffractive pattern disposed at a surface of said objective lens to provide color correction at a predetermined wavelength of light passing therethrough, said diffractive pattern comprising a plurality of spaced ring-shaped steps, each ring concentric with the center of said objective lens and each step having a height equal to said predetermined wavelength, said plurality of ring-shaped steps being formed in accordance with the formula ##EQU3## where:
• Z is Sag value along the z-axis or optical axis
• Y is the semi-diameter height
• CC is the base curvature (i/radius) of the surface
• K is the conic coefficient of the surface
• A, B, C and D are the 4th, 6th, 8th and 10th order aspheric coefficients, respectively
• HOR is the diffraction order, generally 1 or -1
• .lambda. is the design wavelength for the surface
• N1 is the refractive index of the material preceding the diffractive surface
• N2 is the refractive index of the material following the diffractive surface
• C1, C2 and C3 are coefficients for describing aspheric phase departure
• INT is an integer function.