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GETTING ACQUAINTED THE HISTORY OF PHOTOGRAPHY
The early history of photography is rather poorly documented . Important discoveries were made by people who were not at all well known and who left very little , if any , records of what they did and why they did it . Most of the early . discoveries were considered to be scientific curiosities rather than important contributions to a basic field of knowledge . For example , as far back as 350 B.C. Aristotle knew that a tiny hole in a thin sheet of metal could produce an image , but that about as far as it went . Centuries had to pass before someone discovered that a lens could also produce an image but one which was very many times brighter and sharper . It was from this later discovery that the camera obscura developed and from that to the camera itself was not too great a step . However , many scientists and experimenters were involved in this process of discovery and only the names of a relatively small number are now known .
Although we do not know who invented the camera obscura , we do know that in 1553 a man by the name of Giambattista Della Porta wrote about it with the result that for some time he was given credit for its invention . Figure 1 shows such a camera obscura , used primarily as an entertaining toy . However , it didn't take for somebody with a fertile imagination to hit on the idea of making the camera obscura large enough to hold several people , putting the lens overhead and using a mirror to reflect the image onto a sheet of paper on a table or platform where it could be seen more satisfactorily by a number of people . Some landscape artists made use of a camera obscura to help them in their painting , by placing a sheet of paper on the table and tracing the outlines of the image on it . This outline or drawing was subsequently used as many a modern artist uses his preliminary pencil sketches as a basis for his paintings . A camera obscura of this type is shown in Figure 2 .
The next logical step in the history of photography was to find a means of making a permanent record of such a picture on paper or on some other material , and this led to the investigation of the action of light on various materials .
Figure 1 Camera obscura of the type used as an entertaining toy .
Figure 2 Camera obscura used by artist before the days of photography .
As far back as the eighth century , Gerber discovered that silver nitrate became dark on exposure to light , and in 1565 , Fabricus , while in search of gold in the mines of Germany , discovered " horn silver " ore , a crude form of silver chloride . Later it was found that the substance was sensitive to light , and that it could be formed by adding common salt ( sodium chloride ) to a solution of silver nitrate . When freshly made , this silver compound was white but it turned black on exposure to the sun .
In 1727 , J. H. Schulze made a mixture of chalk and silver nitrate solution with which he coated a level surface . He then placed a transparent piece of paper , on which there were some opaque letters in contact with the coated surface and exposed it to the sunlight . The coated surface under the opaque letters remained white , while the surrounding parts turned dark .
In 1777 , Charles William Scheele investigated the behavior of silver chloride under the influence of light . He found that the silver salt was quickly darkened by violet or blue light , while red or yellow light had very little effect upon it . In 1782 , these experiments were confirmed by Senebier who found that blue light would darken the silver chloride in fifteen seconds while it took twenty minutes for red light to have the same effect upon it .
It is reported that in Paris , about the year 1800 , the physicist and lecturer , Jacques Alexandre Cesar Charles , made silhouettes by placing the head of his subjects in a beam of direct sunlight and allowing the shadow of the head to fall upon a piece of paper coated with silver chloride . The result was a white silhouette on a black background .
Silhouettes were very popular in the eighteenth century , and were made then , as now , by cutting profiles out of black paper and pasting them on a white card . Professor Charles obtained a white silhouette on black , but there was no way known at that time of " fixing " this image so that it would not turn black on further exposure to light .
It was not until the beginning of the nineteenth century that the discovery was made that sodium thiosulphate , commonly known as " hypo , " would dissolve the silver salts that had not been affected by light and so " fix " the image ( make it permanent ) by making it no longer sensitive to light .
The discovery of hypo as a fixing agent was made by Sir John Herschel , an English scientist , who also invented the blueprint process . Herschel was also the first to suggest the use of glass as a support for the sensitive emulsion . Hypo was at once adopted by all the experimenters of that time and it is still in use today .
التعرف على تاريخ التصوير ..
GETTING ACQUAINTED THE HISTORY OF PHOTOGRAPHY
The early history of photography is rather poorly documented . Important discoveries were made by people who were not at all well known and who left very little , if any , records of what they did and why they did it . Most of the early . discoveries were considered to be scientific curiosities rather than important contributions to a basic field of knowledge . For example , as far back as 350 B.C. Aristotle knew that a tiny hole in a thin sheet of metal could produce an image , but that about as far as it went . Centuries had to pass before someone discovered that a lens could also produce an image but one which was very many times brighter and sharper . It was from this later discovery that the camera obscura developed and from that to the camera itself was not too great a step . However , many scientists and experimenters were involved in this process of discovery and only the names of a relatively small number are now known .
Although we do not know who invented the camera obscura , we do know that in 1553 a man by the name of Giambattista Della Porta wrote about it with the result that for some time he was given credit for its invention . Figure 1 shows such a camera obscura , used primarily as an entertaining toy . However , it didn't take for somebody with a fertile imagination to hit on the idea of making the camera obscura large enough to hold several people , putting the lens overhead and using a mirror to reflect the image onto a sheet of paper on a table or platform where it could be seen more satisfactorily by a number of people . Some landscape artists made use of a camera obscura to help them in their painting , by placing a sheet of paper on the table and tracing the outlines of the image on it . This outline or drawing was subsequently used as many a modern artist uses his preliminary pencil sketches as a basis for his paintings . A camera obscura of this type is shown in Figure 2 .
The next logical step in the history of photography was to find a means of making a permanent record of such a picture on paper or on some other material , and this led to the investigation of the action of light on various materials .
Figure 1 Camera obscura of the type used as an entertaining toy .
Figure 2 Camera obscura used by artist before the days of photography .
As far back as the eighth century , Gerber discovered that silver nitrate became dark on exposure to light , and in 1565 , Fabricus , while in search of gold in the mines of Germany , discovered " horn silver " ore , a crude form of silver chloride . Later it was found that the substance was sensitive to light , and that it could be formed by adding common salt ( sodium chloride ) to a solution of silver nitrate . When freshly made , this silver compound was white but it turned black on exposure to the sun .
In 1727 , J. H. Schulze made a mixture of chalk and silver nitrate solution with which he coated a level surface . He then placed a transparent piece of paper , on which there were some opaque letters in contact with the coated surface and exposed it to the sunlight . The coated surface under the opaque letters remained white , while the surrounding parts turned dark .
In 1777 , Charles William Scheele investigated the behavior of silver chloride under the influence of light . He found that the silver salt was quickly darkened by violet or blue light , while red or yellow light had very little effect upon it . In 1782 , these experiments were confirmed by Senebier who found that blue light would darken the silver chloride in fifteen seconds while it took twenty minutes for red light to have the same effect upon it .
It is reported that in Paris , about the year 1800 , the physicist and lecturer , Jacques Alexandre Cesar Charles , made silhouettes by placing the head of his subjects in a beam of direct sunlight and allowing the shadow of the head to fall upon a piece of paper coated with silver chloride . The result was a white silhouette on a black background .
Silhouettes were very popular in the eighteenth century , and were made then , as now , by cutting profiles out of black paper and pasting them on a white card . Professor Charles obtained a white silhouette on black , but there was no way known at that time of " fixing " this image so that it would not turn black on further exposure to light .
It was not until the beginning of the nineteenth century that the discovery was made that sodium thiosulphate , commonly known as " hypo , " would dissolve the silver salts that had not been affected by light and so " fix " the image ( make it permanent ) by making it no longer sensitive to light .
The discovery of hypo as a fixing agent was made by Sir John Herschel , an English scientist , who also invented the blueprint process . Herschel was also the first to suggest the use of glass as a support for the sensitive emulsion . Hypo was at once adopted by all the experimenters of that time and it is still in use today .
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