تويت
إضاءة المجال المظلم ..
الإضاءة ..
كتاب التصوير الفوتوغرافي المغلق
Dark field illumination
Dark field illumination is a special kind of trans mitted lighting that lights subjects from below so they appear to glow with a brilliant lumin osity against a black background . It is ideal for emphasizing hairy or spiny edges as well as finely branched subjects , and for revealing the internal structure of translucent subjects . Continuous tungsten lights can be used in dark field set ups , although electronic flash is essen tial for active subjects .
The simplest way to set up dark field illumi nation is to lay a black paper mask with a central hole , having a diameter slightly larger than the subject , on top of a piece of glass . The glass and mask are then raised some six inches above a black velvet background . Either lay the subject directly on the bare glass or , if it is an aquatic organism , place it in a shallow glass dish on the glass . Arrange two or more light sources so that they are directed up toward the subject , but are outside the field of view of the camera . The black mask will screen out all direct light rays passing toward the camera lens , and the subject is lit up by rays which are refracted by it .
As a slight refinement to the set - up described above , I often use a series of small tables , each with different - sized diameter holes . A pair of strip lights secured beneath the table on two opposite sides provides a continuous light source to aid focusing . I make the exposure using two , or sometimes four , small electronic flash guns . When taking photomicrographs ( see p . 142 ) , a black circular stop inserted into the back of the condenser gives a dark field illumination .
Highlighting an open weave ▷ A loosely woven cloth makes a good subject for photography by dark field illumination because the color intensity of each individual thread becomes highlighted . The pattern of the warps and wefts can also be clearly seen at this magnification . To take this picture I cut a piece of cloth and attached it with scotch tape to a square of glass so the cloth was completely parallel to the film plane in the same set - up as for the young trout . Lens Hasselblad 80mm + 77mm ( 55 + 22 ) extension Mag . on film x 1 Mag . on page x4
Revealing the blood vessels
These live young trout , each with their large yellow yolk - sac , came from a trout hatchery . I filtered the cold river water into a small petri dish which I placed on a piece of black velvet over a central hole in a small table , as shown in the set - up on the small flashes placed below the table and angled toward the fish illuminated their translucent bodies , showing the way a major red blood vessel branches across the yellow yolk - sac . Lens 55mm micro - Nikkor Mag . on film × 0.75 Mag . on page × 5
الإضاءة ..
كتاب التصوير الفوتوغرافي المغلق
Dark field illumination
Dark field illumination is a special kind of trans mitted lighting that lights subjects from below so they appear to glow with a brilliant lumin osity against a black background . It is ideal for emphasizing hairy or spiny edges as well as finely branched subjects , and for revealing the internal structure of translucent subjects . Continuous tungsten lights can be used in dark field set ups , although electronic flash is essen tial for active subjects .
The simplest way to set up dark field illumi nation is to lay a black paper mask with a central hole , having a diameter slightly larger than the subject , on top of a piece of glass . The glass and mask are then raised some six inches above a black velvet background . Either lay the subject directly on the bare glass or , if it is an aquatic organism , place it in a shallow glass dish on the glass . Arrange two or more light sources so that they are directed up toward the subject , but are outside the field of view of the camera . The black mask will screen out all direct light rays passing toward the camera lens , and the subject is lit up by rays which are refracted by it .
As a slight refinement to the set - up described above , I often use a series of small tables , each with different - sized diameter holes . A pair of strip lights secured beneath the table on two opposite sides provides a continuous light source to aid focusing . I make the exposure using two , or sometimes four , small electronic flash guns . When taking photomicrographs ( see p . 142 ) , a black circular stop inserted into the back of the condenser gives a dark field illumination .
Highlighting an open weave ▷ A loosely woven cloth makes a good subject for photography by dark field illumination because the color intensity of each individual thread becomes highlighted . The pattern of the warps and wefts can also be clearly seen at this magnification . To take this picture I cut a piece of cloth and attached it with scotch tape to a square of glass so the cloth was completely parallel to the film plane in the same set - up as for the young trout . Lens Hasselblad 80mm + 77mm ( 55 + 22 ) extension Mag . on film x 1 Mag . on page x4
Revealing the blood vessels
These live young trout , each with their large yellow yolk - sac , came from a trout hatchery . I filtered the cold river water into a small petri dish which I placed on a piece of black velvet over a central hole in a small table , as shown in the set - up on the small flashes placed below the table and angled toward the fish illuminated their translucent bodies , showing the way a major red blood vessel branches across the yellow yolk - sac . Lens 55mm micro - Nikkor Mag . on film × 0.75 Mag . on page × 5
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