The MCCD will be undergoing a complete upgrade, including control systems, software, a new data camera, and a new slit and shutter mechanism. To improve image quality throughout the day, a simple, low-order adaptive optics system will also be installed. The adaptive optics system will run with a curvature sensor and bimorph mirror, and use dark, round sunspots as reference objects.
The entire optics bench beyond the image rotator will be redesigned to accomodate the adaptive optics system. After prime focus, an off-center parabolic mirror will be used to image the pupil at the bimorph mirror. The same mirror will then produce a second image plane. The beam will be divided before the image plane to produce a data camera beam and a wavefront sensor beam. The wavefront sensor will consist of a membrane mirror and photodiode array, used to measure the intensity pattern on either side of focus.
The coude focus occurs approximately 600 mm after the image rotator. The first fold mirror, M1, will swing the beam 90 degrees, moving the image plane to the far corner of the bench (as it is presently). A field lens (L1) will be placed here to move the pupil to infinity. A field stop may be placed here to minimize scattered light. Two more fold mirrors (M2 and M3) will wrap the beam back around, in the direction of the off-centered parabolic mirror (M4). This mirror has a diameter of 6 inches and a focal length of 762 mm. Half of the mirror forms a pupil image on the bimorph mirror (M5), 762 mm away and centered on M4. The beam is reflected back to the other half of M4, which forms an image at blah.
Note that the parabolic mirror will introduce a focal plane shift (compare spot diagrams at coude' focus and parabolic mirror focus).
Before the focus of the parabolic mirror, a beamsplitter (BS) will pick off light for the wavefront sensor optics.
The beamsplitter's reflected beam forms the slit relay optical path. Before focus another fold mirror (M6) will direct the beam back along the bench, where a collimating lens (L2), consisting of a Melles Griot 140 mm achromatic doublet will form a pupil image on the scan mirror (SM). From there, another 140 mm achomatic doublet (L3) forms an image on the slit jaws, completing the slit relay optics.
At the image plane of parabolic mirror is a field lens (L4), forming a pupil image on a steering mirror (M7). The field lens is a blah mm achromatic doublet from Spindler and Hoyer. Beyond the steering mirror, another S\&H achromatic doublet (L5) forms an image on the membrane mirror, with a magnification of 1.56. This produces an f/\# on the membrane mirror of 50. Beyond the membrane, another lens produces a pupil image on a 36 element photodiode array.