Maksutov Camera
Introduction
The mirror of the Maksutov camera is spherical and the meniskus corrector lies nearer the mirror than the corrector in a Schmidt camera. Spherical aberration can be corrected for every location of the corrector. Coma can only be corrected for one corrector location. This depends on the thickness and refractive index of the corrector. As the corrector thickness increases, it becomes less strongly curved, and the distance between corrector and the primary at which coma is corrected decreases. Furthermore, the residual aberrations also decrease. Often a corrector thicknes greater than 30 mm is impractical. However, the correction of astigmatism requires a thick corrector.
Designers distinguish between two kinds of meniscus camera systems; those that are concentric, and those that are non-concentric. All the radii, R1, R2 and R3, as well as the radius of the focal surface, have the same center of curvature C. The entrance pupil lies at the center of the system, in front of the meniskus. In this way every entering bundle, whether it is parallel to the mechanical axis or not, has its own optical axis of symmetry with respect to the mirror and the meniscus. Because of this symmetry coma and astigmatism do not occur. Furthermore, sperical aberration can be eliminated almost completely by a meniscus with the proper thickness, radii of curvature and position.
The concentric system has one major disadventage: because of the relatively thick meniscus, it suffers from longitudinal chromatic aberration. Bowers, while emphasizing the advantages of the concentric system, suggests achromatizing the corrector by using two kinds of glass with the same refractive index at the design wavelength but different dispersions. Maksutov found another method of achromatizingn the corrector and he showed that the minimum chromatic aberration of a meniscus for paraxial rays depends on the glass refractive index and both meniscus radii. Maksutov‘s condition means that the meniscus is no longer concentric, ands that its thickness is no longer equal at all places. Because the center of curvature is not at the same position for both optical surfaces, the system cannot be made concentric, so both coma and astigmatism occur, as well as lateral colors. Coma can be eliminated to a large extendt by moving the corrector somewhat toward the mirror.
Another possibility is the Maksutov-Newtonian. In it the Maksutov meniscus corector is placed closer to the mirror than in the original Maksutov camera so the diagonal can be easily attached to the meniscus. The Maksutov-Newtonian is not free of coma, but the aberrations are about half those of comparable Schmidt-Newtonian.
Design and Optimization
The mirror of the Maksutov camera is spherical, and the meniscus corrector lies nearer the mirror than the corrector in a Schmidt camera. Spherical aberration can be corrected for every position of the corrector. Coma can only be corrected for one corrector location. This depends on the thickness and refractive index of the corrector. As the corrector thickness increases, it becomes less strongly curved, and the distance between the corrector and primary mirror at which coma is corrected decreases. Furthermore, the residual aberrations also decrease. However, the correction of astigmatism requires a thick corrector.
The mirror of the Maksutov camera is spherical and the meniskus corrector lies nearer the mirror than the corrector in a Schmidt camera. Spherical aberration can be corrected for every location of the corrector. Coma can only be corrected for one corrector location. This depends on the thickness and refractive index of the corrector. As the corrector thickness increases, it becomes less strongly curved, and the distance between corrector and the primary at which coma is corrected decreases. Furthermore, the residual aberrations also decrease. Often a corrector thicknes greater than 30 mm is impractical. However, the correction of astigmatism requires a thick corrector.
Designers distinguish between two kinds of meniscus camera systems; those that are concentric, and those that are non-concentric. All the radii, R1, R2 and R3, as well as the radius of the focal surface, have the same center of curvature C. The entrance pupil lies at the center of the system, in front of the meniskus. In this way every entering bundle, whether it is parallel to the mechanical axis or not, has its own optical axis of symmetry with respect to the mirror and the meniscus. Because of this symmetry coma and astigmatism do not occur. Furthermore, sperical aberration can be eliminated almost completely by a meniscus with the proper thickness, radii of curvature and position.
The concentric system has one major disadventage: because of the relatively thick meniscus, it suffers from longitudinal chromatic aberration. Bowers, while emphasizing the advantages of the concentric system, suggests achromatizing the corrector by using two kinds of glass with the same refractive index at the design wavelength but different dispersions. Maksutov found another method of achromatizingn the corrector and he showed that the minimum chromatic aberration of a meniscus for paraxial rays depends on the glass refractive index and both meniscus radii. Maksutov‘s condition means that the meniscus is no longer concentric, ands that its thickness is no longer equal at all places. Because the center of curvature is not at the same position for both optical surfaces, the system cannot be made concentric, so both coma and astigmatism occur, as well as lateral colors. Coma can be eliminated to a large extendt by moving the corrector somewhat toward the mirror.
Another possibility is the Maksutov-Newtonian. In it the Maksutov meniscus corector is placed closer to the mirror than in the original Maksutov camera so the diagonal can be easily attached to the meniscus. The Maksutov-Newtonian is not free of coma, but the aberrations are about half those of comparable Schmidt-Newtonian.
Design and Optimization
The mirror of the Maksutov camera is spherical, and the meniscus corrector lies nearer the mirror than the corrector in a Schmidt camera. Spherical aberration can be corrected for every position of the corrector. Coma can only be corrected for one corrector location. This depends on the thickness and refractive index of the corrector. As the corrector thickness increases, it becomes less strongly curved, and the distance between the corrector and primary mirror at which coma is corrected decreases. Furthermore, the residual aberrations also decrease. However, the correction of astigmatism requires a thick corrector.
Applet Tag:
param name = "Title" value = "One Mirror Catadioptric: Maksutov Camera"
param name = "Corrector Diameter" value = "150.0"
param name = "Corrector Thickness" value = "20.0"
param name = "Corrector Glass" value = "BK7"
param name = "Mirror Focal Length" value = "1000.0"
param name = "Half Field Angle" value = "0.45"
param name = "Central Obstruction" value = "0.00"
param name = "Plot Scale" value = "0.020"
param name = "TF Start Angle" value = "0.00"
param name = "TF End Angle" value = "0.45"
param name = "TF Defocus" value = "0.05"
param name = "Number of Arms" value = "36"
param name = "Number of Rings" value = "10"
param name = "Ray Density" value = "10"
param name = "Scale Type Index" value = "3"
param name = "Ray Pattern Index" value = "0"
param name = "Merrit Function Index" value = "2"
param name = "Glass Catalog Index" value = "2"
param name = "Correction Index" value = "0"
param name = "Monochr. Color Index" value = "10"
param name = "WL1 Color Index" value = "1"
param name = "WL2 Color Index" value = "4"
param name = "WL3 Color Index" value = "9"
param name = "Text Color Index" value = "10"