This part mounts the camera onto the body of the microscope, and is the counterpart to the lens spacer. If you are using the lens that came with your webcam, you should probably use this option for the optics module - the one-piece optics module casing replaces this part if you are building a high resolution microscope.
The STL file for this part is called
<camera> is currently either
picamera_2. This allows it to be used with either the $3 6-LED webcams favoured by various low-cost instruments, or the Raspberry Pi camera module.