While presenting a short seminar on photoinstrumentation basics at the NASA Langley Research Center I was myself educated when I came across a piece of imaging gear that begged for applications beyond the ones for which it was being used. The device is a Model 593 electronic memory unit made by Colorado Video. It has applications in motion analysis, surveillance, detection of random events, etc.

This instrument sits between a video camera and a monitor. In "live" mode the device simply allows the live video picture to be displayed on the screen. However, when switched to its active function the device "keys" in the values of the pixels displayed on the screen. As long as the image viewed by the camera does not change the image on the monitor appears very much the same as if one were viewing a live scene.

Now the fun begins. When activated the 593 will, with each frame or field, compare the value of each pixel to its previous value. If the new value is higher, or lower, than some preset value that pixel's value is changed to the new level. Assuming that the device is set to detect a rise in value and assuming also that the background is dark, then dropping a ping-pong ball across the field of view of the camera will record the position of the ball over time at 1/30 or 1/60 second intervals. The image displayed on the monitor can then be "frozen" such that any further changes will not alter the image displayed on the monitor. In this instance the image shown on the screen will very closely resemble what a stroboscope might reveal when used with a conventional still camera except that the pictures can be made in roomlight and the system has all the advantages of electronic imaging media. The images can, of course, be recorded by attaching a VCR to the monitor.

Although I first explored the potential of the 593 as a tool for teaching basic motion analysis applications, later that I realized the device could be used to demonstrate many other "photographic" techniques. This was particularly the case since it occurred to me that the 593 electronic memory actually mimics photographic film in the manner in which it stores image information although it is not a photon-accumulating memory such as film is. One of these later applications was the use of the 593 in the technique described below.

In high magnification imaging it is painfully obvious that as magnification is increased depth-of-field decreases dramatically. Typically photographers overcome this difficulty by stopping the lens down. This raises problems associated with imaging with small apertures and under extreme circumstances may not by itself yield sufficient sharpness in depth.

One solution is to employ a technique that enables great depth to be recorded at the expense of conventional perspective and instantaneous exposure. It is called light scanning photomacrography. The imaging camera is focused on a relatively wide but very thin beam of light often generated by two or three common slide projectors projecting fine slits. Sometimes the lenses are stopped down to increase the distance over which the beams have roughly the same thickness. The individual beams are carefully aligned and superimposed so that they appear to be a single thin beam.

The lens, typically located above the beam is focused on it at the desired magnification. The beam of light is generally made to be narrower than the depth of field of the lens at the chosen aperture. Finally the subject, placed on a sting, is moved towards the beam of light towards the lens.

I set-up a Xybion S9 video camera for photomacrography with an extension tube and a 75mm "C" mount lens and fed the video output of the camera to the Colorado Video 593 set in turn to detect increases in light level. Once I activated the 593 an image could not be seen on the monitor because the beam only illuminated the air below the lens. As the subject broke into the beam that part of it which was detected by the 593 was displayed on the screen. As the subject continued to move upwards, successively lower portions of it were illuminated thus memorized by the 593 and simultaneously displayed on the screen. Since the subject is only detected when its various parts were in the beam of light, in the final "composite" reproduction the image appears uniformly sharp over an extended distance. This effectively appears to increase depth-of-field.

The 593 in effect acted as film would in a conventional camera but it had the added benefit that the process of image acquisition and storage could be perceived in real time. This is invaluable for teaching purposes. The experiment worked perfectly as can be seen from the attached illustrations. Light scanning photomacrography, whether accomplished with conventional film or electronic cameras is a useful technique which yields extended depth at high magnifications.

There are other applications too numerous to mention and I would recommend that you contact the manufacturer for such information or look up a paper by Robert Cadmus, "A video technique to facilitate the visualization of physical phenomena", published in the American Journal of Physics, 58 (4), April 19990.

You can find additional information on light scanning photomacrography here:

Peter Zampol, US Patent 2,928,734, March 1960. A method of Photography.
James Gerakis, "Scanning Light Photomacrography", ITR&D, November 1984, 10-16.
John Turner, "Reasessing the photography of seeds", Functional Photography, March-April 1986, 44-48.
Nile Root, "Deep field photomacrography", Photomethods, May 1986, 16-18.

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CAPTIONS:

1. Video stroboscopic sequence of ping pong ball seen at 1/30 second intervals and a duration of 1/1000 second each time set by camera's electronic shutter.

2. Overall layout of electronic light scanning macrography set-up. Colorado Video 593 located under video monitor, Xybion camera on copy stand, standard Kodak slide projectors set up to project thin beams of light onto subject located between them on a motorized elevating mechanism.

3. Fly on sting attached to motorized elevating mechanism.

4. Instantaneous view of appearance of light beams projected onto fly's head. Lens is focused on the light beam plane.

5. Appearance of stored image information after head of fly passed light beam.

6. Appearance of stored image after fly's thorax had passed through beam.

7. Final image after all of fly had moved up through light beam. Sharp overall.

8. Unscanned image of fly at same aperture as that used during the light scanning process. Note that head and wingtips are unsharp.

Preliminary notes for article above that may form the basis for another, less specific article:

While presenting a short seminar on photoinstrumentation basics at the NASA Langley Research Center I was myself educated to the extent that I came across a pice of imaging gear that begged for applications beyond the opens that it was being used for.

The device in question is an electronic memory unit made by Colorado Video. It is a model 593 device. I am not sure precisely of all the applications for which it is designed but it can obviously be used for motion analysis studies, surveillance purposes, event detection. etc.

This instrument is generally placed between a video camera and a monitor. In "live" mode the device simply allows the live video picture to be displayed ion the screen. When switched to its active function the device "keys" in the values of the pixels displayed on the screen. As long as the image viewed by the camera does not change the image on the monitor appears close to the same as if the camera were viewing a live scene.

Now the fun begins. At this time the 539 device will, with each frame or field, compare the value of each pixel to its previous value and if the new value is higher, or lower, than some preset value that pixel's value is changed to the new level. Assuming that the device is set to detect a rise in value and assuming also that the background is black, then dropping a ping-pong ball across the field of view of the camera will record the position of the ball over time at 1/30 or 1/60 second intervals. The image seen on the monitor then can be "kept" such that any further changes across the camera lens will have no effect on the image shown on the monitor. In this instance the record shown on the screen will very closely resemble what a stroboscope might reveal when used with a conventional still camera except that the pictures can be made in roomlight and the system has all the advantages of electronic imaging media. The images can, of course, be recorded by attaching a VCR to the monitor.

I became involved with the device to try to determine if it could be used effectively as a teaching tool for basic motion analysis applications. It was not until later that I realized the device could be used to demonstrate many other "photographic" phenomena. One of the most amazing of these is described below.

In high magnification imaging it is painfully obvious that as magnification is increased depth-of-field decreases dramatically. Typically photographers overcome this difficulty by stopping the lens down. This raises problems associated with imaging with small aperture and under extreme circumstances may not by itself yield sufficient sharpness in depth anyway.

To overcome this problem, photographers have recently been using a technique called light scanning photomacrography. In this approach the imaging i=s focused on a relatively wide but very thin beam of light often generated by two or three projectors. The individual beams are carefully aligned and superimposed so that they appear to be as much as possible a single thin beam. The lens, typ0ically located above the beam is focused on it at the desired magnification. The beam of light is generally made to be narrower than the depth of field of the lens at the chosen aperture.

Finally the subject, placed on a sting, is moved towards the beam of light towards the lens. At this time the shutter of the camera is opened but since the beam is only illuminating air, no image is formed on the film. As the subject breaks into the beam that part of it which is illuminated is record on the film. As the subject continues to move upwards successively lower portions of it are illuminated and recorded on the film. Since the subject is always illuminated, and thereby, only exposed when its various parts are in the beam of light, in the final reproduction the image appears uniformly sharp over an extended distance. This effectively appears to increase depth-of-field.

I decided to use a Xybion video camera and the 539 unit as combination that woul d detect the passage of various parts of a subject through the beam of light and note the increase in illumination contrasted to a dark background. This 539 would in essence act as film would in a conventional camera but it had the added benefit that the process of image acquisition and storage could be perceived in real time. The experiment worked perfectly as can be seen from the attached illustrations.

In addition to this application, the 539 can also be used to illustrate how focal plane shutters record images and how focal plane shutter distortion is produced. This can be done by pointing the video camera into a black box and having on the front of the box a moving slit through which the camera "scans" the scene as the slit moves across the field of view of the lens. The demonstration is very convincing and students immediately grasp the concept. Soon they are thinking of novel ways to create distortions exploiting the principle of focal plane shutter distortion.

There are many other applications too numerous to mention and I would recommend that you contact the manufacturer for such information. The next article I am working on will describe how to use the device to teach about the operation of focal plane shutters and focal plane shutter distortion, simple peripheral photography done by placing subject on rollers, and also how matte-boxes are used to achieve startling sequential exposure effects.