Houghton Camera
Introduction
In 1944, Houghton suggested a new type of full-aperture corrector for spherical mirrors as an alternative to the hard-to-make Schmidt corrector. These corrector consist of a combination of two or three positive and negative spherical lens that can be considered afocal (i.e., having no optical power) and achromatic. They are over-corrected for spherical aberration in order to compensate for that of the mirror. One special advantage of the Houghton corrector is that its spherical aberration depends on the spacing between the lenses. This means that a residual spherical aberration in the assembled system can be corrected by decreasing or increasing the spacing between the lenses. Houghton pointed out the possibility of using a single type of glass for all of the lenses.
Design and Optimization
For the Houghton camera the mirror is always spherical. The design of a Houghton camera is similar to that for the Schmidt and Wright cameras. Spherical aberration and coma can be corrected for every given position of the corrector. Astigmatism can only be corrected when the corrector is near the center of curvature of the primary.
Optimizing a systems such as the Houghton is more difficult than optimizing a Schmidt or Maksutov system because there are more degrees of freedom. MODAS start with automatically fit of the optimal bending factor, and the correspond radii of curvature of both lenses in pairs at the same rate. The distance between the lenses is another free parameter to test for its effect, but such changes should be made systematically (only when color aberration cannot be suppressed sufficiently with lenses made of the same glass, should the designer resort latter in surface editor, to two different glasses with the same design index but different dispersion). Spherical aberration must be eliminated. Unless the axial spot diagram is smaller than the Airy disk, the system will never have value as an astronomical telescope.
In 1944, Houghton suggested a new type of full-aperture corrector for spherical mirrors as an alternative to the hard-to-make Schmidt corrector. These corrector consist of a combination of two or three positive and negative spherical lens that can be considered afocal (i.e., having no optical power) and achromatic. They are over-corrected for spherical aberration in order to compensate for that of the mirror. One special advantage of the Houghton corrector is that its spherical aberration depends on the spacing between the lenses. This means that a residual spherical aberration in the assembled system can be corrected by decreasing or increasing the spacing between the lenses. Houghton pointed out the possibility of using a single type of glass for all of the lenses.
Design and Optimization
For the Houghton camera the mirror is always spherical. The design of a Houghton camera is similar to that for the Schmidt and Wright cameras. Spherical aberration and coma can be corrected for every given position of the corrector. Astigmatism can only be corrected when the corrector is near the center of curvature of the primary.
Optimizing a systems such as the Houghton is more difficult than optimizing a Schmidt or Maksutov system because there are more degrees of freedom. MODAS start with automatically fit of the optimal bending factor, and the correspond radii of curvature of both lenses in pairs at the same rate. The distance between the lenses is another free parameter to test for its effect, but such changes should be made systematically (only when color aberration cannot be suppressed sufficiently with lenses made of the same glass, should the designer resort latter in surface editor, to two different glasses with the same design index but different dispersion). Spherical aberration must be eliminated. Unless the axial spot diagram is smaller than the Airy disk, the system will never have value as an astronomical telescope.
Applet Tag:
- param name = "Title" value = "One Mirrror Catadioptric: Houghton Camera"
- param name = "Corrector Diameter" value = "200.0"
- param name = "Edge Thickness Lens A" value = "10.0"
- param name = "Center Thickness Lens B" value = "10.0"
- param name = "Corrector Location" value = "1000.0"
- param name = "Lens Glass" value = "BK7"
- param name = "Primary 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 = "0.025"
- 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 = "Lens Catalog Index" value = "2"
- 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"