مزيد من التجارب .. داجوير .. التعرف على تاريخ التصوير .. التصوير الفوتوغرافي الحديث

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  • مزيد من التجارب .. داجوير .. التعرف على تاريخ التصوير .. التصوير الفوتوغرافي الحديث

    التصوير الفوتوغرافي الحديث
    التعرف على تاريخ التصوير ..
    تجارب أخرى .. داجوير

    FURTHER EXPERIMENTS

    In the meantime , Thomas Wedgwood and Sir Humphrey Davy were experi menting along the same lines as Professor Charles . They coated paper and white leather with a solution of silver nitrate and , after placing an opaque object on the top of this prepared paper , exposed it to sunlight . The unprotected portion darkened , while the protected part remained white .

    These two experimenters then tried using this coated paper under paintings on glass . The rays of light passing through the transparent and semi - transparent portions of the painting , darkened the paper and gave them a negative picture . They also found that the blue rays of light were much more effective than red and yellow rays .

    These two men made some progress but they , too , like Professor Charles , were stopped by the fact that they could not make their pictures permanent .

    Thomas Wedgwood and Sir Humphrey Davy experimented with the camera obscura by allowing the image to fall on a sheet of sensitized paper , but the coating was too insensitive for the light to make much of an impression on it .

    About 1814 , Joseph Nicephore Niepce , a French chemist , began his photographic experiments . During the years from 1823 to 1825 he worked to produce asphaltum photographs on glass and metal . He coated large sheets with a thin layer of bitumen ( natural asphalt ) dissolved in oil of lavender . He exposed this to light under a drawing on paper that had been varnished to make it more transparent . After an exposure of about an hour to strong sunlight , the bitumen on the metal that had been protected from the light by the opaque parts of the drawing was washed away with oil of lavender , leaving a negative image of the drawing . After washing off the soluble bitumen that was not affected by the exposure to light , he applied an acid to eat away the metal . This process is still used in a modified form for making some types of printing plates .

    DAGUERRE

    Perhaps the best known of these early experimenters is Louis Jacques Mande Daguerre , the inventor of the Daguerreotype process . Daguerre was born near Paris in 1787 and about 1824 he began experimenting to find a way of fixing the image produced in the camera . He was a scenic painter and used the camera as a help in reproducing natural scenes .

    Daguerre was quite unsuccessful in these experiments , but he did not give up . He neglected his scenic painting business and devoted himself to these unsuccessful experiments so assiduously that his wife became alarmed as to his sanity . In 1829 Daguerre and Niepce entered into partnership under which each agreed to share with the other any discoveries either might make .

    In 1837 , Daguerre quite accidentally discovered what is now known as the Daguerreotype process . He was using metal plates coated with a combination of silver and iodine and after two or three hours exposure in the camera he would get a faint image on the metal plate . One day , as Daguerre was making an exposure , the sun went behind some clouds so that there was not enough light to give him a good picture . He , therefore , discontinued the exposure and put away the lightly exposed plate in his chemical cabinet , intending to use it again when the sun was shining . The next morning , to his pleasure and surprise , upon picking up this plate , he found it to have a distinct and perfect picture . He coated another
    plate , underexposed it , and placed it in the " magic - cabinet " overnight . The next morning he found another beautiful picture .

    Daguerre did not know what caused this strange development of the picture . Using the process of elimination , he exposed plate after plate and with each exposure certain chemicals were removed from the cabinet . Finally he found that the vapor from a bowl of mercury was the developing agent .

    Daguerre kept the process he had discovered a secret until June 1839 when he published the details at the request of the French government . He was awarded an annual life pension of six thousand francs .

    These Daguerreotypes were beautiful and have never been surpassed for delicacy of tone . Actually they are very thin negatives backed with silver or other metal . Being negatives , they are reversed as to right and left .

    In Daguerre's time the plates used , coated with iodine , required an exposure of from five to thirty minutes . The process was modified later so that the exposure was reduced to about thirty seconds . In those days having a portrait taken was quite an ordeal .

    A few months before the publication of Daguerre's process , Henry Fox Talbot , who had been experimenting with coated paper and leather , showed the results of these experiments at the Royal Society . These he called " photogenic drawings . " Talbot produced an image on paper , whereas Daguerre's was an image on a polished silver surface .

    The calotype or talbotype process was patented by Talbot in 1841. This was the third British patent for photography , the two previous ones having been granted to Daguerre . This patent was granted for a process for obtaining a negative on paper . It was very popular for several years but was later superseded by the collodion process .

    In 1843 , Talbot patented the use of sodium thiosulfate ( hypo ) for making pictures permanent . This process had been suggested in 1819 by Sir John Herschel . In 1854 , Talbot coated paper with albumen to produce a glossy surface .

    Other experimenters , Le Gray , Hunt and Pollock , worked on this idea in 1851 , 1852 and 1853 , and for many years albumen paper was one of the most popular of printing processes . It was supreme until the introduction of gelatino - chloride paper commonly called P.O.P. - printing - out paper , as distinguished from developing paper .


    اضغط على الصورة لعرض أكبر.   الإسم:	مستند جديد ٠٧-٠٨-٢٠٢٣ ١٥.١٧ (1).jpg  مشاهدات:	0  الحجم:	40.1 كيلوبايت  الهوية:	143909 اضغط على الصورة لعرض أكبر.   الإسم:	مستند جديد ٠٧-٠٨-٢٠٢٣ ١٥.٢٣_1.jpg  مشاهدات:	0  الحجم:	133.7 كيلوبايت  الهوية:	143910 اضغط على الصورة لعرض أكبر.   الإسم:	مستند جديد ٠٧-٠٨-٢٠٢٣ ١٥.٢١.jpg  مشاهدات:	0  الحجم:	133.6 كيلوبايت  الهوية:	143911

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