OM blue detector with filter wheel

The OM was originally designed to carry two different types of detectors, one blue and one red, named after the part of the optical spectrum where they have their maximum sensitivity, with a beam-splitting dichroic mirror in front of the two detectors. After a design change, there are now only two blue OM detectors (in cold redundancy; i.e. only one OR the other can be operated), with a reflective mirror in front. The view presented in this photo follows the way of the incoming light, which will pass through filters on the (now empty) filter wheel slots.

Photo courtesy of Mullard Space Science Laboratory, England.