Grism wheel

Some problems occurred with time-out of the grism wheels which is somehow related to the balance of this wheel, though it is not clear how this can cause the problem. Later models of FOSC's have a different design in the way the wheels are driven and they do not seem to have this problem. It was checked with Niels Michaelsen in Copenhagen what the difference are, but it turns-out that modifying the current wheel to a similar design would be a major operation.