Below is an extract from a Blogger blog:
The image below was created using 35mm negatives that had been taken using a Pentax SP1000 camera. All Pentax Spotmatics (SP) use the M42 screw-thread lens mount. The lenses are focused at maximum aperture to give a bright viewfinder image for focusing, then a switch at the side stops the lens down and switches on the metering to enable the exposure to be set prior to shutter release. The photographs below were taken in 1981 and 2012 and merged together in March 2013.