aka.anzi
High Speed Photography 40,000 fps analogue camera. E Bamber
Photo of a 32 sided glass polygon prism above used in high speed analogue photography.
(ref the geometry of triacontadigon.)
In the mid 1960s while working in the USA I was a production engineer in precision optics for a well known company specialising in military and aerospace products. One of my projects had been the design of procedures, manufacturing processes and tool design for components in high speed cameras, rated at 10,000 / 20,000 / 40,000 fps . The camera optics, excluding the objectives of each system, consisted ten or so precision prisms and lenses and one polygon prism.
I only describe here some aspects of the manufacture and function of the 32 sided optical polygon for the 40,000 fps quarter frame systems. This polygon is an extremely critical element in the 40,000 fps quarter frame system; a very precise costly optical glass element to manufacture.
A brief outline:
1, The polygon here is 26mm dia X 16mm. it is mounted/ cemented between two balanced matching metal disks very slightly larger in diameter than the polygon. The metal disks are designed with sprockets around their circumference in order to engage with the film perforations. This assembly is then optically aligned onto a shaft and bearings. Any deviation of the final assembled unit from the vertical and while rotating at high speeds will produce unacceptable images.
In these cameras the entire spool of film traverses in a matter of seconds from one spool to the other at very high speeds across the unit holding the polygon. It is the speed of the film engaging in sync with the sprockets that rotates the polygon unit at ~75,000 rpm.
The optical image from the objective lens and internal optical prisms then pass through the rotating polygon onto the moving film. The images are exposed onto the film (in a swiping fashion) at 32 frames for each revolution of the polygon, equiv.to 40,000 frames per second,.
2. To meet the specifications. The polygon faces are ground and polished flat to 1/20th wavelength, sodium D line; and to the highest surface quality. The opposite polished surfaces of the polygon have to be parallel with each other, the angular tolerances within 0.2and 0.5 seconds of arc, non accumulative. For this accuracy it was necessary at stages during manufacturing to employ interferometry and precision theodolite inspection methods.
Interestingly, filming only lasts a few seconds and ends with a loud bang caused by the speed of the exiting film tail. I had seen many example photographs from the cameras and including one of a missile entering the engine pod of an in flight jet fighter.
Optical designers n.b. There is extreme difficulty in obtaining 32 equal precision surfaces on polygon prisms of this relatively small diameter; the above photographed polygon for 40,000 fps was a reject for that reason.
E Bamber , Glasgow.
High Speed Photography 40,000 fps analogue camera. E Bamber
Photo of a 32 sided glass polygon prism above used in high speed analogue photography.
(ref the geometry of triacontadigon.)
In the mid 1960s while working in the USA I was a production engineer in precision optics for a well known company specialising in military and aerospace products. One of my projects had been the design of procedures, manufacturing processes and tool design for components in high speed cameras, rated at 10,000 / 20,000 / 40,000 fps . The camera optics, excluding the objectives of each system, consisted ten or so precision prisms and lenses and one polygon prism.
I only describe here some aspects of the manufacture and function of the 32 sided optical polygon for the 40,000 fps quarter frame systems. This polygon is an extremely critical element in the 40,000 fps quarter frame system; a very precise costly optical glass element to manufacture.
A brief outline:
1, The polygon here is 26mm dia X 16mm. it is mounted/ cemented between two balanced matching metal disks very slightly larger in diameter than the polygon. The metal disks are designed with sprockets around their circumference in order to engage with the film perforations. This assembly is then optically aligned onto a shaft and bearings. Any deviation of the final assembled unit from the vertical and while rotating at high speeds will produce unacceptable images.
In these cameras the entire spool of film traverses in a matter of seconds from one spool to the other at very high speeds across the unit holding the polygon. It is the speed of the film engaging in sync with the sprockets that rotates the polygon unit at ~75,000 rpm.
The optical image from the objective lens and internal optical prisms then pass through the rotating polygon onto the moving film. The images are exposed onto the film (in a swiping fashion) at 32 frames for each revolution of the polygon, equiv.to 40,000 frames per second,.
2. To meet the specifications. The polygon faces are ground and polished flat to 1/20th wavelength, sodium D line; and to the highest surface quality. The opposite polished surfaces of the polygon have to be parallel with each other, the angular tolerances within 0.2and 0.5 seconds of arc, non accumulative. For this accuracy it was necessary at stages during manufacturing to employ interferometry and precision theodolite inspection methods.
Interestingly, filming only lasts a few seconds and ends with a loud bang caused by the speed of the exiting film tail. I had seen many example photographs from the cameras and including one of a missile entering the engine pod of an in flight jet fighter.
Optical designers n.b. There is extreme difficulty in obtaining 32 equal precision surfaces on polygon prisms of this relatively small diameter; the above photographed polygon for 40,000 fps was a reject for that reason.
E Bamber , Glasgow.