Optics
Each LBC contains a total of six lenses, including the cryostat windows. The LBC-Blue lenses are made of fused silica for high transmission in the UBV wavelengths. The LBC-Red lenses are BK7 borosilicate for better performance in the V-Z wavelengths. The figure below shows the structure of the LBCs, with the diameter (in mm) of the optical elements for each side. The final focal ratio of the corrector is F/1.47.
Two filter wheels are located between the final two elements, the last of which being the almost-zero-power cryostat window.
LBC-Blue was installed first, and vignetting was discovered at the corners of the array. The optics were redesigned to reduce this in LBC-Red (see Focal Plane Layout). The total throughput is 84% for LBC-Blue, and 82% for LBC-Red, not including filters.
LBC optical elements. The diameters are shown in mm.
Optical distortion maps for LBC-Blue. For LBC-Blue, the circles mark the 1%, 1.5% and 2% distortion limits.
Optical distortion maps for LBC-Red. For LBC-Red, the circles mark the 2% and 3% distortion limits.
