Patent ID: 7154669

Claim:
An optical system corrected for intrinsic birefringence, comprising: a first pair of optical elements disposed along an optical axis, said first pair including: a first optical element made up of a first material having a first intrinsic birefringence sign and a first crystal axis; and a second optical element made up of said first material having a second intrinsic birefringence sign and a second crystal axis; a second pair of optical elements disposed along said optical axis, said second pair including: a third optical element made up of a second material having a third intrinsic birefringence sign and a third crystal axis; and a fourth optical element made up of said second material having a fourth intrinsic birefringence sign and a fourth crystal axis; wherein said first material is different from said second material; wherein said first pair of optical elements has a first type of refractive power, and said second pair of optical elements has a second type of refractive power; and wherein the first type of refractive power, the second type of refractive power and the first to fourth intrinsic birefringence signs tend to correct for intrinsic birefringence, and wherein said first and second optical elements are rotated with respect to one another such that the first crystal axis and the second crystal axis form a first angle which tends to correct for intrinsic birefringence; and wherein said third and fourth optical elements are rotated with respect to one another such that the third crystal axis and the fourth crystal axis form a second angle which tends to correct for intrinsic birefringence.