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history of the camera
electromagnetic waves
electrical resistance
energy from the sun
magic lantern
A Short History Of The Camera - The Photophone
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A Short History Of the Camera  -  The Photophone

The following Article is a suggestion, and a rather interesting one at that, so without further adieu:

Although the device I'm about to exhibit here is not related to cameras, although in this author's mind, deserves a place in the history of the camera. The photophone not only offers the interesting story in inventions, it serves as an excellent lesson in getting the human voice to ride on the electromagnetic waves... in fact, using visible (white) light to do it!

Why Not Vibrate the Reflective Surface with the Voice?

Outlandish an idea this actually is, for all the likelihood of any one of variables to be off, seems more of an accident.

However, in 1839 A. E. Becquerel noted that crystalline selenium, when used as an electrical conductor, exhibits a marked change in the material's electrical resistance. It was this discovery that marked the earliest attempts at transmitting and receiving sound "over the air."

The receiving end of the apparatus had been discovered, and it was thought that a beam of sunlight captured by a series of mirrors and optics (similar to the magic lantern) could then be directed a reflective diaphragm which would then create modulation of the light energy. The modulations would then be picked up by the receiver. This is made possible by the constant light energy from the sun.

The Parabolic Mirror Makes Transduction on the Receiving End Possible

The use of a parabolic mirror would direct the energy to a focal point at which a carrier with crystalline selenium cells were located. This is where the signal is transduced into electrical energy, which was further transduced by means of a diaphragm, which vibrated with the incoming electrical energy containing the data. The diaphragm would then convert the signal back to sound waves which are then audible.

A parabolic mirror is a cone-shaped surface designed to capture incoming light energy and project it to a focal point in the midst of the cone. A transducer was usually place at this point, such as the crystalline selenium mentioned above.

Inventors toyed around with this phenomenon in the years between Becquerel's discovery and Marconi's wireless. In the 1860s, the Scottish physicist, James Clerk Maxwell suspected that "radio" waves exist

In 1886, Heinrich Rudolph Hertz discovered that these radio waves could be used much in the same way as carrier waves, based on the earlier Becquerel experiments.

Modulating the Light Source

Not long after the discovery of the electrical properties of crystalline selenium, a dentist, Mahlon Loomis was experimenting with the radio wave concept, was able to note changes in electrical current could be represented over the air and picked up by a receiver, producing the same fluctuations. The experiment entailed the use of two kites, both of which had meters attached to them. The electrical current, intercepted by a diaphragm was fed the sound energy through the simple transducer, was picked up by the receiver and successfully restored through the receiving transducer and converted back to sound through an earpieces equipped with a diaphragm.

It would not be until Guglielmo Marconi came along in 1895 demonstrating that sound would be successfully transmitted and received in the form of wireless telegraphy ...or radio as we know it. During the period, there was widespread experimentation going on with photography as well. It was only natural that men would be attracted to the possibility of applying light energy to sound. Even today, experimentation goes on and many great breakthroughs, both in today’s cameras and audio recorders. It is very interesting to note that, at one time, visible light was used to transmit sound and light at the same time! Although this proved impractical, it is a very important step in today's latest photo technology, both in light and sound.

To Recap the Above:

  • The photophone was an early invention using carrier waves to transmit sound over the air.
  • The objective here was to send a voice signal from the source to a target a significant distance away.
  • Transduction to pick up the sound was first noted when crystalline selenium was charged with electricity. It was found that light energy affected the resistance of the medium when focused onto it with a parabolic mirror.
  • The transmitter transducer was easily figured out and implemented. It was simply a reflective material that was easily vibrated by the voice (or any other sounds the device was sensitive enough to pick up.
  • This was the forerunner of Marconi’s wireless telegraphy, which is the beginnings of radio as we know it.

Today, light and sound are easily packaged into small units we now know as digital camera technology and beyond. We often take for granted what we have and is the purpose of the History of the Camera Series of articles to give attention to the background of today’s technology for greater appreciation.


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