This is an adapter to mount a Canon EF mount camera to a Nikon research microscope.
The adapter was designed for a TE2000E microscope but might well fit other Eclipse series microscopes. It fits the side ports but not the dedicated camera front port.
The image circle should cover an APS-C sensor fine, for a FF sensor it might be too small. We use a an EOS 550D (EOS Rebel T2i). The focus point between nosepiece and the camera is close, although not perfect. After all it is not a precision piece.
The author marked this model as their own original creation.