A single-lens reflex (SLR) camera is camera that uses a semi-automatic moving mirror system which permits the photographer to sometimes see exactly what will be captured by the film or digital imaging system, as opposed to pre-SLR cameras where the view through the viewfinder could be significantly different from what was captured on film.
Prior to the development of SLR, all cameras with viewfinders had two optical light paths: one path through the lens to the film, and another path positioned above (TLR or twin-lens reflex) or to the side (rangefinder). Because the viewfinder and the film lens cannot share the same optical path, the viewing lens is aimed to intersect with the film lens at a fixed point somewhere in front of the camera. This is not problematic for pictures taken at a middle or longer distance but parallax causes framing errors in close-up shots. Moreover, focusing the lens of a non-reflex camera when it is opened to wider apertures (such as in low light or while using low-speed film) is not easy.
Most SLR cameras permit upright and laterally correct viewing through use of a pentaprism situated in the optical path between the reflex mirror and viewfinder. Light is reflected by a movable mirror upwards into the pentaprism where it is reflected several times until it aligns with the viewfinder. When the shutter is released, the mirror moves out of the light path and the light shines directly onto the film, or in the case of a DSLR, the CCD or CMOS imaging sensor.
Focus can be adjusted manually by the photographer or automatically by an autofocus system. The viewfinder can include a matte focusing screen located just above the mirror system to diffuse the light. This system permits accurate viewing, composing and focusing, especially useful with interchangeable lenses.
Up until the 1990s, SLR was the most advanced photographic preview system available, but the recent development and refinement of digital imaging technology with an on-camera live LCD preview screen has overshadowed SLR's popularity. Nearly all inexpensive compact digital cameras now include an LCD preview screen allowing the photographer to see exactly what the CCD is capturing. However, SLR is still popular in high-end and professional cameras, because the pixel resolution, contrast ratio, refresh rate, and color gamut of an LCD preview screen cannot compete with the clarity and shadow detail of a direct-viewed optical SLR viewfinder.
mercoledì 2 dicembre 2009
War photography
War photography captures images of armed conflict and life in war-torn areas, beginning with Roger Fenton's photographs of the Crimean War of 1853-56, in which he was limited by his bulky equipment and the technology of the day, which had not yet developed a method for photographing moving objects.
The photography of war depicts the terrors of war mingled with acts of sacrifice. Different to paintings or drawings of war, photographic images are not easily altered; although in some cases, photographers manipulate the subjects and scenes depicted in a work, resulting in an image that is not completely objective in nature.
Photography, presented to the public in 1839, was believed to create images that were accurate representations of the world. Photography was used to record historical information, but not always in the optimistic way that was conceived at the advent of the medium.
It was anticipated that photographers, supposedly not acting as active participants of war but as neutral partisan, would be able to bring their cumbersome photographic equipment into the battlefield and record the rapid action of combat. This was not the case, as the technical insufficiency of the photograph in recording movement was not considered. The daguerreotype, an early form of photography that generated a single image using a silver-coated copper plate, took a very long time to produce. This prevented action photography, as images took minutes to develop and could not be processed immediately.
Valley of the Shadow of Death, with road full of cannonballs, by Roger Fenton in the Crimea, 1855
The first war photographer was an anonymous American who took a number of daguerrotypes during the Mexican–American War, in 1847[1]. The first known war photographer is the Hungarian-Romanian Carol Popp de Szathmàri who took photos of various officers in 1853 and of war scenes near Oltenita and Silistra in 1854, during the Crimean War. He created some 200 pictures albums, which he personally offered in 1855 to Napoleon III of France and Queen Victoria of the United Kingdom. About 9 of his pictures survive today[2]. The French photographer Ernest Edouard de Caranza caught his countrymans in their camp near Varna, in 1854. He was followed by Roger Fenton, in 1855, although with his bulky equipment he was limited to posed still photographs or landscapes. He took a large van and an assistant, and returned to Britain with over 350 usable large format negatives.
The inability of the early photograph to record a moving object lead to the practice of recreating scenes of battle, such as in the work of both Haley Sims and Alexander Gardner. They admittedly reconfigured scenes that took place during the American Civil War (1861-1865) in order to intensify the visual and emotional effects of battle.[3] Alexander Gardner and Matthew Brady rearranged bodies of dead soldiers during the Civil War in order to create a clear picture of the atrocities associated with battle. In Soldiers on the Battlefield, 1862, Brady produced a controversial tableau of the dead within a desolate landscape. This work, along with Alexander Gardner’s 1863 work Home of a Rebel Sharpshooter[4] were images, which, when shown to the public, brought home the horrific reality of war.[5]
A Wehrmacht combat photographer on the Eastern Front, 1941.
Since early photographers were not able to create images of moving targets, they would record more sedentary aspects of war, such as fortifications, soldiers, and land before and after battle along with the re-creation of action scenes. Similar to battle photography, portrait images of soldiers were also often staged. In order to produce a photograph, the subject had to be perfectly still for a matter of minutes, so they were posed to be comfortable and minimize movement.
Unlike paintings, which presented a single illustration of a specific event, photography offered the opportunity for an extensive amount of images to enter circulation. The proliferation of the photographic images allowed the public to be well informed in the discourses of war. The advent of mass-reproduced images of war were not only used to inform the public but they served as imprints of the time and as historical recordings.[6] Mass-produced images did have consequences. Besides informing the public, the glut of images in distribution over-saturated the market, allowing viewers to develop the ability to disregard the immediate value and historical importance of certain photographs.
The photography of war depicts the terrors of war mingled with acts of sacrifice. Different to paintings or drawings of war, photographic images are not easily altered; although in some cases, photographers manipulate the subjects and scenes depicted in a work, resulting in an image that is not completely objective in nature.
Photography, presented to the public in 1839, was believed to create images that were accurate representations of the world. Photography was used to record historical information, but not always in the optimistic way that was conceived at the advent of the medium.
It was anticipated that photographers, supposedly not acting as active participants of war but as neutral partisan, would be able to bring their cumbersome photographic equipment into the battlefield and record the rapid action of combat. This was not the case, as the technical insufficiency of the photograph in recording movement was not considered. The daguerreotype, an early form of photography that generated a single image using a silver-coated copper plate, took a very long time to produce. This prevented action photography, as images took minutes to develop and could not be processed immediately.
Valley of the Shadow of Death, with road full of cannonballs, by Roger Fenton in the Crimea, 1855
The first war photographer was an anonymous American who took a number of daguerrotypes during the Mexican–American War, in 1847[1]. The first known war photographer is the Hungarian-Romanian Carol Popp de Szathmàri who took photos of various officers in 1853 and of war scenes near Oltenita and Silistra in 1854, during the Crimean War. He created some 200 pictures albums, which he personally offered in 1855 to Napoleon III of France and Queen Victoria of the United Kingdom. About 9 of his pictures survive today[2]. The French photographer Ernest Edouard de Caranza caught his countrymans in their camp near Varna, in 1854. He was followed by Roger Fenton, in 1855, although with his bulky equipment he was limited to posed still photographs or landscapes. He took a large van and an assistant, and returned to Britain with over 350 usable large format negatives.
The inability of the early photograph to record a moving object lead to the practice of recreating scenes of battle, such as in the work of both Haley Sims and Alexander Gardner. They admittedly reconfigured scenes that took place during the American Civil War (1861-1865) in order to intensify the visual and emotional effects of battle.[3] Alexander Gardner and Matthew Brady rearranged bodies of dead soldiers during the Civil War in order to create a clear picture of the atrocities associated with battle. In Soldiers on the Battlefield, 1862, Brady produced a controversial tableau of the dead within a desolate landscape. This work, along with Alexander Gardner’s 1863 work Home of a Rebel Sharpshooter[4] were images, which, when shown to the public, brought home the horrific reality of war.[5]
A Wehrmacht combat photographer on the Eastern Front, 1941.
Since early photographers were not able to create images of moving targets, they would record more sedentary aspects of war, such as fortifications, soldiers, and land before and after battle along with the re-creation of action scenes. Similar to battle photography, portrait images of soldiers were also often staged. In order to produce a photograph, the subject had to be perfectly still for a matter of minutes, so they were posed to be comfortable and minimize movement.
Unlike paintings, which presented a single illustration of a specific event, photography offered the opportunity for an extensive amount of images to enter circulation. The proliferation of the photographic images allowed the public to be well informed in the discourses of war. The advent of mass-reproduced images of war were not only used to inform the public but they served as imprints of the time and as historical recordings.[6] Mass-produced images did have consequences. Besides informing the public, the glut of images in distribution over-saturated the market, allowing viewers to develop the ability to disregard the immediate value and historical importance of certain photographs.
Street photography
Street photography is a type of documentary photography that features subjects in candid situations within public places such as streets, parks, beaches, malls, political conventions, and other settings.
Street photography uses the techniques of straight photography in that it shows a pure vision of something, like holding up a mirror to society. Street photography often tends to be ironic and can be distanced from its subject matter, and often concentrates on a single human moment, caught at a decisive or poignant moment. On the other hand, much street photography takes the opposite approach and provides a very literal and extremely personal rendering of the subject matter, giving the audience a more visceral experience of walks of life they might only be passingly familiar with. In the 20th century, street photographers have provided an exemplary and detailed record of street culture in Europe and North America, and elsewhere to a somewhat lesser extent.
Many classic works of street photography were created in the period between roughly 1890 and 1975 and coincided with the introduction of portable cameras, especially small 35mm, rangefinder cameras. Classic practitioners of street photography include Henri Cartier-Bresson, Robert Frank, Alfred Eisenstaedt, W. Eugene Smith, William Eggleston, Brassa?, Willy Ronis, Robert Doisneau and Garry Winogrand.
Street photography uses the techniques of straight photography in that it shows a pure vision of something, like holding up a mirror to society. Street photography often tends to be ironic and can be distanced from its subject matter, and often concentrates on a single human moment, caught at a decisive or poignant moment. On the other hand, much street photography takes the opposite approach and provides a very literal and extremely personal rendering of the subject matter, giving the audience a more visceral experience of walks of life they might only be passingly familiar with. In the 20th century, street photographers have provided an exemplary and detailed record of street culture in Europe and North America, and elsewhere to a somewhat lesser extent.
Many classic works of street photography were created in the period between roughly 1890 and 1975 and coincided with the introduction of portable cameras, especially small 35mm, rangefinder cameras. Classic practitioners of street photography include Henri Cartier-Bresson, Robert Frank, Alfred Eisenstaedt, W. Eugene Smith, William Eggleston, Brassa?, Willy Ronis, Robert Doisneau and Garry Winogrand.
Bokeh
In photography, bokeh is the blur,[1][2] or the æsthetic quality of the blur,[3][4][5] in out-of-focus areas of an image, or "the way the lens renders out-of-focus points of light."[6] Differences in lens aberrations and aperture shape cause some lens designs to blur the image in a way that is pleasing to the eye, while others produce blurring that is unpleasant or distracting— "good" or "bad" bokeh, respectively.[1] Bokeh occurs for parts of the scene that lie outside the depth of field. Photographers sometimes deliberately use a shallow focus technique to create images with prominent out-of-focus regions.
Bokeh is often most visible around small background highlights, such as specular reflections and light sources, which is why it often associated with such areas.[1] However, bokeh is not limited to highlights, as blur occurs in all out-of-focus regions of the image.
The term comes from the Japanese word boke (?? or ??), which means "blur" or "haze", or boke-aji (???), the "blur quality". The Japanese term boke is also used in the sense of a mental haze or senility.[7]
The English spelling bokeh was popularized in 1997 in Photo Techniques magazine, when Mike Johnston, the editor at the time, commissioned three papers on the topic for the March/April 1997 issue; he altered the spelling to suggest the correct pronunciation to English speakers, saying "it is properly pronounced with bo as in bone and ke as in Kenneth, with equal stress on either syllable".[2] Bokeh replaced the previous spelling boke that had been in use at least since 1996, when Merklinger had also suggested "or Bokeh if you prefer."[8]
The term bokeh has appeared in photography books at least since 1998.[9] It is sometimes pronounced /'bo?k?/ (boke-uh[10]).
[edit] Description
An extremely shallow depth of field, a common effect of macro lenses, emphasizes bokeh
The depth of field is the region where the size of the circle of confusion is less than the resolution of the human eye. Circles with a diameter less than the circle of confusion will appear to be in focus.
Although difficult to quantify, some lenses enhance overall image quality by producing more subjectively pleasing out-of-focus areas. Good bokeh is especially important for large-aperture lenses, macro lenses, and long telephoto lenses because they are typically used with a shallow depth of field. Bokeh is also important for medium telephoto "portrait lenses" (typically 85–150 mm on 35-mm format) because in portraiture photography, the photographer typically seeks to obtain a shallow depth of field to achieve an out-of-focus background and make the subject stand out.
The bokeh produced by a Catadioptric lens (also called a mirror lens).
Bokeh characteristics may be quantified by examining the image's circle of confusion. In out-of-focus areas, each point of light becomes an image of the aperture, generally a more or less round disc. Depending how a lens is corrected for spherical aberration, the disc may be uniformly illuminated, brighter near the edge, or brighter near the center. Lenses that are poorly corrected for spherical aberration will show one kind of disc for out-of-focus points in front of the plane of focus, and a different kind for points behind. This may actually be desirable, as blur circles that are dimmer near the edges produce less-defined shapes which blend smoothly with the surrounding image. Lens manufacturers including Nikon, Canon, and Minolta make lenses designed with specific controls to change the rendering of the out-of-focus areas.
Catadioptric lens bokeh seen in more detail.
The shape of the aperture has a great influence on the subjective quality of bokeh. When a lens is stopped down to something other than its maximum aperture size (minimum f-number), out-of-focus points are blurred into the polygonal shape of the aperture rather than perfect circles. This is most apparent when a lens produces undesirable, hard-edged bokeh, therefore some lenses have aperture blades with curved edges to make the aperture more closely approximate a circle rather than a polygon. Lens designers can also increase the number of blades to achieve the same effect. Traditional "Portrait" lenses, such as the "fast" 85mm focal length models for 35mm cameras often feature almost circular aperture diaphragms, as is the case with Canon's EF 85mm f/1.2L II lens and Nikon's 85mm f/1.4D, and are generally considered exceptional performers. A catadioptric telephoto lens displays bokehs resembling doughnuts, because its secondary mirror blocks the central part of the aperture opening. Recently, photographers have found how to exploit the shape of the bokehs by creating a simple mask out of card with the shape that the photographer wishes the bokeh to be, and placing it over the lens. Common shapes are stars and hearts, but it is possible to create it with almost any shape imagined.[11]
Leica lenses, especially vintage ones, are often claimed to excel in bokeh quality, although Leica photographers have tended to make more use of maximum aperture due to the lenses' ability to maintain good sharpness at wide openings and the suitability of the Leica camera system for available-light theatre work and reportage. Consequently, more evidence is needed to determine whether Leica's lens designers deliberately set out to produce pleasing bokeh.
Minolta/Sony STF 135mm f/2.8 [T4.5]* (STF standing for Smooth Transition Focus) is a lens which is specifically designed to produce pleasing bokeh. An apodization filter is used to soften the aperture edges which results in a smooth defocused area with gradually fading circles. Those qualities make it the only lens of this kind currently on the market.
No bokeh
Faux (synthetic) bokeh
Recently, a research group at MIT Media Lab showed that the bokeh effect can be used to make imperceptibly small barcodes, or bokodes. By using markers as small as 2.5 microns, if the marker is viewed out of focus through an ordinary camera, the resulting bokeh is large enough to scan the information in the barcode.[12]
Bokeh is often most visible around small background highlights, such as specular reflections and light sources, which is why it often associated with such areas.[1] However, bokeh is not limited to highlights, as blur occurs in all out-of-focus regions of the image.
The term comes from the Japanese word boke (?? or ??), which means "blur" or "haze", or boke-aji (???), the "blur quality". The Japanese term boke is also used in the sense of a mental haze or senility.[7]
The English spelling bokeh was popularized in 1997 in Photo Techniques magazine, when Mike Johnston, the editor at the time, commissioned three papers on the topic for the March/April 1997 issue; he altered the spelling to suggest the correct pronunciation to English speakers, saying "it is properly pronounced with bo as in bone and ke as in Kenneth, with equal stress on either syllable".[2] Bokeh replaced the previous spelling boke that had been in use at least since 1996, when Merklinger had also suggested "or Bokeh if you prefer."[8]
The term bokeh has appeared in photography books at least since 1998.[9] It is sometimes pronounced /'bo?k?/ (boke-uh[10]).
[edit] Description
An extremely shallow depth of field, a common effect of macro lenses, emphasizes bokeh
The depth of field is the region where the size of the circle of confusion is less than the resolution of the human eye. Circles with a diameter less than the circle of confusion will appear to be in focus.
Although difficult to quantify, some lenses enhance overall image quality by producing more subjectively pleasing out-of-focus areas. Good bokeh is especially important for large-aperture lenses, macro lenses, and long telephoto lenses because they are typically used with a shallow depth of field. Bokeh is also important for medium telephoto "portrait lenses" (typically 85–150 mm on 35-mm format) because in portraiture photography, the photographer typically seeks to obtain a shallow depth of field to achieve an out-of-focus background and make the subject stand out.
The bokeh produced by a Catadioptric lens (also called a mirror lens).
Bokeh characteristics may be quantified by examining the image's circle of confusion. In out-of-focus areas, each point of light becomes an image of the aperture, generally a more or less round disc. Depending how a lens is corrected for spherical aberration, the disc may be uniformly illuminated, brighter near the edge, or brighter near the center. Lenses that are poorly corrected for spherical aberration will show one kind of disc for out-of-focus points in front of the plane of focus, and a different kind for points behind. This may actually be desirable, as blur circles that are dimmer near the edges produce less-defined shapes which blend smoothly with the surrounding image. Lens manufacturers including Nikon, Canon, and Minolta make lenses designed with specific controls to change the rendering of the out-of-focus areas.
Catadioptric lens bokeh seen in more detail.
The shape of the aperture has a great influence on the subjective quality of bokeh. When a lens is stopped down to something other than its maximum aperture size (minimum f-number), out-of-focus points are blurred into the polygonal shape of the aperture rather than perfect circles. This is most apparent when a lens produces undesirable, hard-edged bokeh, therefore some lenses have aperture blades with curved edges to make the aperture more closely approximate a circle rather than a polygon. Lens designers can also increase the number of blades to achieve the same effect. Traditional "Portrait" lenses, such as the "fast" 85mm focal length models for 35mm cameras often feature almost circular aperture diaphragms, as is the case with Canon's EF 85mm f/1.2L II lens and Nikon's 85mm f/1.4D, and are generally considered exceptional performers. A catadioptric telephoto lens displays bokehs resembling doughnuts, because its secondary mirror blocks the central part of the aperture opening. Recently, photographers have found how to exploit the shape of the bokehs by creating a simple mask out of card with the shape that the photographer wishes the bokeh to be, and placing it over the lens. Common shapes are stars and hearts, but it is possible to create it with almost any shape imagined.[11]
Leica lenses, especially vintage ones, are often claimed to excel in bokeh quality, although Leica photographers have tended to make more use of maximum aperture due to the lenses' ability to maintain good sharpness at wide openings and the suitability of the Leica camera system for available-light theatre work and reportage. Consequently, more evidence is needed to determine whether Leica's lens designers deliberately set out to produce pleasing bokeh.
Minolta/Sony STF 135mm f/2.8 [T4.5]* (STF standing for Smooth Transition Focus) is a lens which is specifically designed to produce pleasing bokeh. An apodization filter is used to soften the aperture edges which results in a smooth defocused area with gradually fading circles. Those qualities make it the only lens of this kind currently on the market.
No bokeh
Faux (synthetic) bokeh
Recently, a research group at MIT Media Lab showed that the bokeh effect can be used to make imperceptibly small barcodes, or bokodes. By using markers as small as 2.5 microns, if the marker is viewed out of focus through an ordinary camera, the resulting bokeh is large enough to scan the information in the barcode.[12]
Light painting
Light painting, also known as light drawing or light graffiti is a photographic technique in which exposures are made usually at night or in a darkened room by moving a hand-held light source or by moving the camera. In many cases the light source itself does not have to appear in the image. The term light painting also encompasses images lit from outside the frame with hand-held light sources.
The light can either be used to selectively illuminate parts of the subject or to "paint" a picture by shining it directly into the camera lens. Light painting requires a sufficiently slow shutter speed, usually a second or more. Like night photography, it has grown in popularity since the advent of digital cameras because they allow photographers to see the results of their work immediately.
Light painting can take on the characteristics of a quick pencil sketch. Pablo Picasso was photographed in 1949 doing a quick sketch in the air.[1]
Flash lights or light pens can also be used to create Full Bleed images. Different colored lights can be used to project an image on the CCD.
[edit] Moving the camera
Light painting by moving the camera, also called camera painting, is the antithesis of traditional photography. At night, or in a dark room, the camera can be taken off the tripod and used like a paintbrush. An example is using the night sky as the canvas, the camera as the brush and cityscapes (amongst other light sources) as the palette. Putting energy into moving the camera by stroking lights, making patterns and laying down backgrounds can create abstract artistic images. Also known as "Camera Toss."
Making a light painting doesn't necessarily need to be done in a dark room or at night. Sometimes using artificial light, like LEDs and mobile phones, or through the limited sunlight beaming in a curtained room creates a shadowing effect. Using a mirror creates a double image, which adds up to a more creative result.
[edit] Technique and equipment
Light photo of a glowsticking dance.
A variety of light sources can be used, ranging from simple flashlights to dedicated devices like the Hosemaster, which uses a fiber optic light pen.[2] Other sources of light including candles, matches, lighter flints, glowsticks, and Poi are also popular.
A tripod is usually necessary due to the long exposure times involved. Alternatively, the camera may be placed on or braced against a table or other solid support. A shutter release cable or self timer is generally employed in order to minimize camera shake. Color Gels can also be used to color the light sources.
Manual focus is often used since autofocus systems may not perform well in low light. In addition, photographers often use a slow film speed or low ISO setting on a digital sensor to minimize grain (or digital noise) and increase exposure tolerance, as evaluating exposure is often tricky.
The light can either be used to selectively illuminate parts of the subject or to "paint" a picture by shining it directly into the camera lens. Light painting requires a sufficiently slow shutter speed, usually a second or more. Like night photography, it has grown in popularity since the advent of digital cameras because they allow photographers to see the results of their work immediately.
Light painting can take on the characteristics of a quick pencil sketch. Pablo Picasso was photographed in 1949 doing a quick sketch in the air.[1]
Flash lights or light pens can also be used to create Full Bleed images. Different colored lights can be used to project an image on the CCD.
[edit] Moving the camera
Light painting by moving the camera, also called camera painting, is the antithesis of traditional photography. At night, or in a dark room, the camera can be taken off the tripod and used like a paintbrush. An example is using the night sky as the canvas, the camera as the brush and cityscapes (amongst other light sources) as the palette. Putting energy into moving the camera by stroking lights, making patterns and laying down backgrounds can create abstract artistic images. Also known as "Camera Toss."
Making a light painting doesn't necessarily need to be done in a dark room or at night. Sometimes using artificial light, like LEDs and mobile phones, or through the limited sunlight beaming in a curtained room creates a shadowing effect. Using a mirror creates a double image, which adds up to a more creative result.
[edit] Technique and equipment
Light photo of a glowsticking dance.
A variety of light sources can be used, ranging from simple flashlights to dedicated devices like the Hosemaster, which uses a fiber optic light pen.[2] Other sources of light including candles, matches, lighter flints, glowsticks, and Poi are also popular.
A tripod is usually necessary due to the long exposure times involved. Alternatively, the camera may be placed on or braced against a table or other solid support. A shutter release cable or self timer is generally employed in order to minimize camera shake. Color Gels can also be used to color the light sources.
Manual focus is often used since autofocus systems may not perform well in low light. In addition, photographers often use a slow film speed or low ISO setting on a digital sensor to minimize grain (or digital noise) and increase exposure tolerance, as evaluating exposure is often tricky.
Macro photography
Macro photography is close-up photography. The classical definition is that the image projected on the "film plane" (i.e., film or a digital sensor) is close to the same size as the subject. On 35 mm film (for example), the lens is typically optimized to focus sharply on a small area approaching the size of the film frame. Most 35mm format macro lenses achieve at least 1:2, that is to say, the image on the film is 1/2 the size of the object being photographed. Many 35mm macro lenses are 1:1, meaning the image on the film is the same size as the object being photographed. Another important distinction is that lenses designed for macro are usually at their sharpest at macro focus distances and are not quite as sharp at other focus distances.
In recent years, the term macro has been used in marketing material to mean being able to focus on a subject close enough so that when a regular 6×4 inch (15×10 cm) print is made, the image is life-size or larger. With 35mm film this requires a magnification ratio of only approximately 1:4, which demands less of lens quality than 1:1. With digital cameras the actual image size is rarely stated, so that the magnification ratio is largely irrelevant; cameras instead advertise their closest focusing distance.
Macroscopy competes with the digital microscope where a small camera tube can be attached directly to a computer, usually by a USB port. Macroscopy also competes with photomicroscopy, and it is much less expensive to achieve high quality images. However, high magnification images are more difficult using macroscopy.
The method is especially useful in forensic work, where small details at crime or accident scenes may often be significant. Trace evidence such as fingerprints and skid marks is especially important, and easily recorded using macroscopy. Fracture surfaces from broken products are very revealing using fractography, especially when photographed using glancing light to highlight surface details.
In recent years, the term macro has been used in marketing material to mean being able to focus on a subject close enough so that when a regular 6×4 inch (15×10 cm) print is made, the image is life-size or larger. With 35mm film this requires a magnification ratio of only approximately 1:4, which demands less of lens quality than 1:1. With digital cameras the actual image size is rarely stated, so that the magnification ratio is largely irrelevant; cameras instead advertise their closest focusing distance.
Macroscopy competes with the digital microscope where a small camera tube can be attached directly to a computer, usually by a USB port. Macroscopy also competes with photomicroscopy, and it is much less expensive to achieve high quality images. However, high magnification images are more difficult using macroscopy.
The method is especially useful in forensic work, where small details at crime or accident scenes may often be significant. Trace evidence such as fingerprints and skid marks is especially important, and easily recorded using macroscopy. Fracture surfaces from broken products are very revealing using fractography, especially when photographed using glancing light to highlight surface details.
Selective focus
Depth of field can be anywhere from a fraction of a millimeter to virtually infinite. In some cases, such as landscapes, it may be desirable to have the entire image sharp, and a large DOF is appropriate. In other cases, artistic considerations may dictate that only a part of the image be in focus, emphasizing the subject while de-emphasizing the background, perhaps giving only a suggestion of the environment (Langford 1973, 81). For example, a common technique in melodramas and horror films is a closeup of a person's face, with someone just behind that person visible but out of focus. A portrait or close-up still photograph might use a small DOF to isolate the subject from a distracting background. The use of limited DOF to emphasize one part of an image is known as selective focus, differential focus or shallow focus.
Although a small DOF implies that other parts of the image will be unsharp, it does not, by itself, determine how unsharp those parts will be. The amount of background (or foreground) blur depends on the distance from the plane of focus, so if a background is close to the subject, it may be difficult to blur sufficiently even with a small DOF. In practice, the lens f-number is usually adjusted until the background or foreground is acceptably blurred, often without direct concern for the DOF.
Sometimes, however, it is desirable to have the entire subject sharp while ensuring that the background is sufficiently unsharp. When the distance between subject and background is fixed, as is the case with many scenes, the DOF and the amount of background blur are not independent. Although it is not always possible to achieve both the desired subject sharpness and the desired background unsharpness, several techniques can be used to increase the separation of subject and background.
For a given scene and subject magnification, the background blur increases with lens focal length. If it is not important that background objects be unrecognizable, background de-emphasis can be increased by using a lens of longer focal length and increasing the subject distance to maintain the same magnification. This technique requires that sufficient space in front of the subject be available; moreover, the perspective of the scene changes because of the different camera position, and this may or may not be acceptable.
Selective focus using tilt with a Lensbaby
The situation is not as simple if it is important that a background object, such as a sign, be unrecognizable. The magnification of background objects also increases with focal length, so with the technique just described, there is little change in the recognizability of background objects.[4] However, a lens of longer focal length may still be of some help; because of the narrower angle of view, a slight change of camera position may suffice to eliminate the distracting object from the field of view.
Although tilt and swing are normally used to maximize the part of the image that is within the DOF, they also can be used, in combination with a small f-number, to give selective focus to a plane that isn't perpendicular to the lens axis. With this technique, it is possible to have objects at greatly different distances from the camera in sharp focus and yet have a very shallow DOF. The effect can be interesting because it differs from what most viewers are accustomed to seeing.
Although a small DOF implies that other parts of the image will be unsharp, it does not, by itself, determine how unsharp those parts will be. The amount of background (or foreground) blur depends on the distance from the plane of focus, so if a background is close to the subject, it may be difficult to blur sufficiently even with a small DOF. In practice, the lens f-number is usually adjusted until the background or foreground is acceptably blurred, often without direct concern for the DOF.
Sometimes, however, it is desirable to have the entire subject sharp while ensuring that the background is sufficiently unsharp. When the distance between subject and background is fixed, as is the case with many scenes, the DOF and the amount of background blur are not independent. Although it is not always possible to achieve both the desired subject sharpness and the desired background unsharpness, several techniques can be used to increase the separation of subject and background.
For a given scene and subject magnification, the background blur increases with lens focal length. If it is not important that background objects be unrecognizable, background de-emphasis can be increased by using a lens of longer focal length and increasing the subject distance to maintain the same magnification. This technique requires that sufficient space in front of the subject be available; moreover, the perspective of the scene changes because of the different camera position, and this may or may not be acceptable.
Selective focus using tilt with a Lensbaby
The situation is not as simple if it is important that a background object, such as a sign, be unrecognizable. The magnification of background objects also increases with focal length, so with the technique just described, there is little change in the recognizability of background objects.[4] However, a lens of longer focal length may still be of some help; because of the narrower angle of view, a slight change of camera position may suffice to eliminate the distracting object from the field of view.
Although tilt and swing are normally used to maximize the part of the image that is within the DOF, they also can be used, in combination with a small f-number, to give selective focus to a plane that isn't perpendicular to the lens axis. With this technique, it is possible to have objects at greatly different distances from the camera in sharp focus and yet have a very shallow DOF. The effect can be interesting because it differs from what most viewers are accustomed to seeing.
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