This is a picture of my new de Wijs stereo macro lens setup

The lens is pretty small, but has a large focus guide bolted to it. The focus guide has a white platform that begins about an inch from the focus posts. This white platform serves to reflect light up into the subject. I've found that the subject should be roughly parallel to the front of the focus posts to be at the plane of sharpest focus, although I am still trying to get the hang of it. The view in the viewfinder is very dark, and rather small. The lens assembly projects 2 images onto the sensor, one for each "eye" viewpoint for the stereo image.

You have to separate the images and process them in post. I have created a Photoshop action that cuts the right image into a separate layer, moves it on top of the left image, and then blacks out the red channel of the right eye image and the green and blue channels of the left eye image, then sets the blend mode of the top layer to "screen", which adds the light from both layers together. I then have to shift the two images manual to adjust the registration and apparent depth of the image. Interestingly, the top-to-bottom registration of the left and right eye images seems a little off. I have to shift one of the images up to adjust, in addition to shifting side to side to fine-tune the "zero crossing point" of the image (the place where the left and right eye views match up, and that appears to be on the surface of the display.)