It looks like a way to project a microfilm image onto a table top.
I followed the link and found http://www.chilton-computing.org.uk/gallery/ral/slide3.htm . The bottom-right corner is this image, with the title "Scanning Lab". It's also visible, without a projected image, in the image at the top-left. ( http://www.chilton-computing.org.uk/gallery/ral/orig/r02008.... )
The machine in the background appears to be a digitizer, given the image on the bottom row, center http://www.chilton-computing.org.uk/gallery/ral/orig/r03354.... .
Edit: oops! I pointed to an image from the same photo session, but this Linux Voice article uses the upper-left photo at http://www.chilton-computing.org.uk/gallery/ral/slide4.htm . That is, LV uses http://www.chilton-computing.org.uk/gallery/ral/orig/r03357.... and not http://www.chilton-computing.org.uk/gallery/ral/orig/r03356.... . Note that the Chilton Computing web site dates the images as 26.07.68.
