Image Details
Caption: Figure 15.
Each as-built petal was robotically surveyed and aligned such that fiber tips, fiducials, and cameras, when installed, would land in focus on DESI's nominal aspheric focal surface. The upper-left and lower-right photos show the FPR and petals being surveyed in a CMM at LBNL. The two photos at the lower left show the GFA camera mount plate on a petal, which is adjusted by shimming at its three mount screws. At the upper right, a stack of two gauge blocks and an aluminum retention/contact pad are seen at the corner of a petal. Each petal has two of these, which contact the FPR, and give us both stiff mounting and fine tilt adjustment. Not shown in these photos are two additional adjustment features of the petals: these are captive shim stacks at (1) the outer radius, to set the focal position, and (2) at the inner radius Figure 11, to equalize the petals with respect to each other at their tips. Over the set of all 12 petals (10 installed plus two spares), we achieved 12 μm rms, 33 μm max error in our alignment.
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