Collimator Alignment No Title Setting up the focus

Camera Alignment

The camera was aligned to be self consistent prior to shipping to La Palma, and should not need re-aligning for some considerable time. The The camera is evacuated to approximately 10 millibars, and cryogenically cooled during use. If it is kept at its operating temperature (150 K) immediately following pump down, the outgassing rate is sufficiently low that the camera should not need repumping for three weeks or so. As the camera is kept below a few millibars at all times, and is not opened in normal service, the coating of the primary should remain in good condition for the lifetime of the instrument. The only possible reason the camera should need to be opened is either due to chip failure, or, most likely, for a chip upgrade. In this case, a minimal amount of checking of the alignment will be necessary, and the following procedure should be followed.

Assuming the camera is in the reflection position, is at room temperature, and vented to atmospheric pressure, then remove the relay mirror R-1. Set up a laser on the baseplate of R , adjusting it to get it squared on to the camera corrector. Remove the front end of the camera by removing the 16 M6 bolts around the rim. Pull carefully away from the camera body in a straight line (to avoid damaging the CCD and field lens mounting rings). Disconnect the CCD connectors, disconnect the cold finger, disconnect the CCD rotation adjuster and remove the CCD ring, complete with the CCD.

To set the components back onto the optical axis, place a perforated target in front of the laser. Assuming there is no need to adjust the camera primary, then adjust the position of the field flattening lens to centre the back reflections and interference pattern onto the laser beam. Replace and reconnect the CCD mounting ring. Note that a sheet of indium foil is required between the cold finger from the CCD ring, and the cold finger from the cryostat, to improve the thermal contact. Replace the front end of the camera, making sure the springs are bearing correctly on the the CCD and field lens mounting rings, and there is no dirt or fleck on the `O' rings sealing the front end to the main camera body. Pull the two together using the 16 M16 bolts, making sure the front rim is pulled down squarely, Check that the back reflection from the camera corrector is still squared onto the laser.

The focus of WYFFOS will need to be checked after any dismantling of the camera. Experience has shown that it is possible to dismantle and rebuild the camera without disturbing the mutual alignment of the components.

Collimator Alignment No Title Setting up the focus