Bean discovered the hard way just how sensitive the SEC pickup tube can be. It's very sensitive, militarily so. The SEC tube in the Westinghouse cameras was one of the few items on Apollo that was classified at the time of the mission, but of course has been declassified now for a long time.
And yes, the SEC was capable of imaging stars. It was designed for night vision. Yes, the Apollo 11 crew carried a lens for it that could open to f/1 and, if pointed carefully, could have imaged the stars or photographed the lunar night side using only earthshine. The iris on that lens was preset to f/22 as it was deployed on the MESA to capture Neil Armstrong coming down the ladder. That was an appropriate iris setting for objects lit only indirectly and is stopped down too far to see stars. Armstrong replaced that lens with one that offered an f/50 setting for photographing sunlit objects with the incredibly sensitive tube. Again, too stopped down for stars also to be visible.