jrk has made much in his DAC footage posts about the use of a mirror, finding it to be suspicious for some reason or other. I decided (because that, jrk, is what inquiring minds do) to look into it a little more.
This is the 16mm mounting we're used to seeing - the famous image from inside the LM:
It's on what is obviously a mount that allows for a degree of flexibility in where the camera is pointed; the LM could land on sloping ground, it might end up with a window in the sun, or be pointed vertically downwards to film the ascent back to orbit.
It's also somewhat intrusive, liable to be knocked.
Here's a view of the camera, and you can see the important part fitted to the side of the it:
That attachment allows it to slide inside a grooved mount, where it can be gripped securely. I've circled the part doing the gripping in the Apollo 11 image.
The camera mount for the CSM was in the rendez-vous window, which was angled upwards so that they could view the rendez-vous and docking. Here's a photo of Apollo 9's, but they are all the same:
It's more important here to know that your camera is pointing in the right direction. The position of the mount means that the camera can be mounted flush with the CSM body - nicely out of the way. It's good design for a small space. How to they resolve the problem that the lens is not pointing of the window?
Answers on a postcard...