SM independent exposure control

If I remember well, some years ago, they was a request from IPMU to have a separate control of the two shutters of a Spectrograph Module.

I just wanted to clarify one point on the hardware configurations: the red shutters is placed just before the first dichroic, so when the Red shutter is closed, none of CUs see light (Blue, Red and NIR).

If the Blue shutter is open while Red shutter is closed, Blue CU will only scattered light due to white coating on the red shutter (done for the back illumination)

If the Blue shutter is close and Red Shutter is open, only Red and NIR CU will see light.

This has an impact on the exposure control, I don't what is the intend on that but I think it was important to point out this hardware limitation