Apogee CCD Shutter

The Andor/Apogee U16 camera that is in use on many of our telescopes requires almost no routine maintenance. Since the primary window is covered when the shutter is closed, it acquires very little dust and only occasional cleaning which is done with a dry air puff while the shutter is open for a long exposure.

A older camera that had become unresponsive was returned to Andor for service and as part of that work they installed an entirely new second generation F-series electronics. Upon testing after its return, we noticed that the shutter did not reliably close while the camera was on the telescope. A visual inspection showed light dewing on the CCD chamber's exterior window, and the shutter did not close on its own even with power removed.

The U16 has an internal iris shutter with a solenoid actuator to open the shutter by retracting a plunger that is attached to the iris mechanism. A view of the interior of the camera is shown below:

The shutter's return to a closed state occurs when power is taken off the solenoid and the coil spring pulls in the opposite direction of the plunger to return the iris blades back over the aperture. The tension in the spring is adjustable by the position of the small bracket held by two screws that go through slots in the bracket. In the case of this misbehaving camera, we found that the spring was not under tension at all in its returned state, and that pull of the spring on the shutter iris was weak when it was extended by the solenoid. It is possible that the bracket had slipped or was not adjusted during repair, and it is a simple adjustment to add tension to the spring so that the shutter closes after an exposure.