I don't believe in doing superimposed effects -- too complicated. My preference is to get everything to fit in the view-finder before shooting. The UFO was made by cutting a piece of paper into a lense shape, then shading the top part grey and the bottom black. (I would have done red and white, but on the train at the time, I did not have anything to do colours.) When the UFO was stuck to the window of my train compartment, the result through the movie camera's viewfinder did not look half bad. The "saucer" looked kind of fuzzy because it was so close to the camera lense, and the background looked equally fuzzy because it was being seen through the two sheets of glass of the train window.
For over a minute I took a continuous shot of a disc-shaped object over the Nullarbor. It gained altitude, lost altitude, moved closer, then ended its stint of train-following with a sudden streak to the horizon. (When you pan and zoom the right way the result can look really wild. One of the things I wanted to check when the film came back was if sharpness of focus of the UFO changed as it "receeded". It did not seem to, looking at it through the view-finder.) When I took the still photograph, part of the window frame got into shot in the upper right. Foreground blurring is caused by the train's movement.