Depth of field deutsch

depth of field deutsch

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In some cases, rotating the POF can better fit the DOF to the scene, and achieve the required sharpness at a smaller f -number.

Alternatively, rotating the POF, in combination with a small f -number, can minimize the part of an image that is within the DOF. For a given subject framing and camera position, the DOF is controlled by the lens aperture diameter, which is usually specified as the f-number , the ratio of lens focal length to aperture diameter.

Reducing the aperture diameter increasing the f -number increases the DOF because the circle of confusion is shrunk directly and indirectly by reducing the light hitting the outside of the lens which is focused to a different point than light hitting the inside of the lens due to spherical aberration caused by the construction of the lens; [7] however, it also reduces the amount of light transmitted, and increases diffraction , placing a practical limit on the extent to which DOF can be increased by reducing the aperture diameter.

Motion pictures make only limited use of this control; to produce a consistent image quality from shot to shot, cinematographers usually choose a single aperture setting for interiors and another for exteriors, and adjust exposure through the use of camera filters or light levels.

Aperture settings are adjusted more frequently in still photography, where variations in depth of field are used to produce a variety of special effects.

The advent of digital technology in photography has provided additional means of controlling the extent of image sharpness; some methods allow extended DOF that would be impossible with traditional techniques, and some allow the DOF to be determined after the image is made.

Focus stacking is a digital image processing technique which combines multiple images taken at different focal distances to give a resulting image with a greater depth of field than any of the individual source images.

Getting sufficient depth of field can be particularly challenging in macro photography. The images to the right illustrate the extended DOF that can be achieved by combining multiple images.

Wavefront coding is a method that convolves rays in such a way that it provides an image where fields are in focus simultaneously with all planes out of focus by a constant amount.

A plenoptic camera uses a microlens array to capture 4D light field information about a scene. Colour apodization is a technique combining a modified lens design with image processing to achieve an increased depth of field.

The lens is modified such that each colour channel has a different lens aperture. Therefore, the blue channel will have a greater depth of field than the other colours.

The image processing identifies blurred regions in the red and green channels and in these regions copies the sharper edge data from the blue channel.

The result is an image that combines the best features from the different f -numbers, Kay In , Nokia implemented DOF control in some of its high-end smartphones , called Refocus, which can change a picture's depth of field after the picture is taken.

It works best when there are close-up and distant objects in the frame. If the camera position and image framing i.

Because of diffraction, however, this isn't really true. Once a lens is stopped down to where most aberrations are well corrected, stopping down further will decrease sharpness in the plane of focus.

At the DOF limits, however, further stopping down decreases the size of the defocus blur spot, and the overall sharpness may still increase.

Eventually, the defocus blur spot becomes negligibly small, and further stopping down serves only to decrease sharpness even at DOF limits Gibson , For general photography, diffraction at DOF limits typically becomes significant only at fairly large f -numbers; because large f -numbers typically require long exposure times, motion blur may cause greater loss of sharpness than the loss from diffraction.

That lens includes distance scales in feet and meters; when a marked distance is set opposite the large white index mark, the focus is set to that distance.

The DOF scale below the distance scales includes markings on either side of the index that correspond to f -numbers. When the lens is set to a given f -number, the DOF extends between the distances that align with the f -number markings.

Conversely, the required focus and f -number can be determined from the desired DOF limits by locating the near and far DOF limits on the lens distance scale and setting focus so that the index mark is centered between the near and far distance marks.

The required f -number is determined by finding the markings on the DOF scale that are closest to the near and far distance marks Ray , The focus so determined would be about 1.

The DOF limits can be determined visually, by focusing on the farthest object to be within the DOF and noting the distance mark on the lens distance scale, and repeating the process for the nearest object to be within the DOF.

Using other distances for DOF limits requires visual interpolation between marked distances. Since the distance scale is nonlinear, accurate interpolation can be difficult.

In most cases, English and metric distance markings are not coincident, so using both scales to note focused distances can sometimes lessen the need for interpolation.

Many autofocus lenses have smaller distance and DOF scales and fewer markings than do comparable manual-focus lenses, so that determining focus and f -number from the scales on an autofocus lens may be more difficult than with a comparable manual-focus lens.

In most cases, determining these settings using the lens DOF scales on an autofocus lens requires that the lens or camera body be set to manual focus.

On a view camera, the focus and f -number can be obtained by measuring the focus spread and performing simple calculations.

The procedure is described in more detail in the section Focus and f -number from DOF limits. Some view cameras include DOF calculators that indicate focus and f -number without the need for any calculations by the photographer Tillmanns , 67—68; Ray , — The hyperfocal distance is the nearest focal distance at which the DOF extends to infinity; focusing the camera at the hyperfocal distance results in the largest possible depth of field for a given f -number Ray , Focusing beyond the hyperfocal distance does not increase the far DOF which already extends to infinity , but it does decrease the DOF in front of the subject, decreasing the total DOF.

Some photographers consider this wasting DOF; however, see Object field methods above for a rationale for doing so.

Focusing on the hyperfocal distance is a special case of zone focusing in which the far limit of DOF is at infinity.

If the lens includes a DOF scale, the hyperfocal distance can be set by aligning the infinity mark on the distance scale with the mark on the DOF scale corresponding to the f -number to which the lens is set.

Some cameras have their hyperfocal distance marked on the focus dial. For example, on the Minox LX focusing dial there is a red dot between 2 m and infinity; when the lens is set at the red dot, that is, focused at the hyperfocal distance, the depth of field stretches from 2 m to infinity.

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 , 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.

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.

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. When the subject is at the hyperfocal distance or beyond, the far DOF is infinite, so the ratio is 1: For large apertures at typical portrait distances, the ratio is still close to 1: As a lens is stopped down, the defocus blur at the DOF limits decreases but diffraction blur increases.

The presence of these two opposing factors implies a point at which the combined blur spot is minimized Gibson , 64 ; at that point, the f -number is optimal for image sharpness.

If the final image is viewed under normal conditions e. But this may not be true if the final image is viewed under more demanding conditions, e.

Hansma also suggests that the final-image size may not be known when a photograph is taken, and obtaining the maximum practicable sharpness allows the decision to make a large final image to be made at a later time.

Hansma and Peterson have discussed determining the combined effects of defocus and diffraction using a root-square combination of the individual blur spots.

Hansma's approach determines the f -number that will give the maximum possible sharpness; Peterson's approach determines the minimum f -number that will give the desired sharpness in the final image, and yields a maximum focus spread for which the desired sharpness can be achieved.

Gibson , 64 gives a similar discussion, additionally considering blurring effects of camera lens aberrations, enlarging lens diffraction and aberrations, the negative emulsion, and the printing paper.

Hopkins , Stokseth , and Williams and Becklund have discussed the combined effects using the modulation transfer function.

In semiconductor photolithography applications, depth of field is extremely important as integrated circuit layout features must be printed with high accuracy at extremely small size.

The difficulty is that the wafer surface is not perfectly flat, but may vary by several micrometres. Even this small variation causes some distortion in the projected image, and results in unwanted variations in the resulting pattern.

Thus photolithography engineers take extreme measures to maximize the optical depth of field of the photolithography equipment.

To minimize this distortion further, semiconductor manufacturers may use chemical mechanical polishing to make the wafer surface even flatter before lithographic patterning.

A person may sometimes experience better vision in daylight than at night because of an increased depth of field due to constriction of the pupil i.

The basis of these formulas is given in the section Derivation of the DOF formulae ; [17] refer to the diagram in that section for illustration of the quantities discussed below.

Thus, for a given image format, depth of field is determined by three factors: For close-up work, the hyperfocal distance has little applicability, and it usually is more convenient to express DOF in terms of image magnification.

In other words, for the same subject magnification, at the same f -number, all focal lengths used on a given image format give approximately the same DOF.

The discussion thus far has assumed a symmetrical lens for which the entrance and exit pupils coincide with the front and rear nodal planes , and for which the pupil magnification the ratio of exit pupil diameter to that of the entrance pupil [18] is unity.

Although this assumption usually is reasonable for large-format lenses, it often is invalid for medium- and small-format lenses.

When the pupil magnification is unity, this equation reduces to that for a symmetrical lens. Except for close-up and macro photography, the effect of lens asymmetry is minimal.

At unity magnification, however, the errors from neglecting the pupil magnification can be significant. If only working f -number is directly available, the following formula can be used instead:.

When the subject distance is large in comparison with the lens focal length, the required f -number is.

In practice, these settings usually are determined on the image side of the lens, using measurements on the bed or rail with a view camera, or using lens DOF scales on manual-focus lenses for small- and medium-format cameras.

In practical terms, focus is set to halfway between the near and far image distances. The required f -number is. The image distances are measured from the camera's image plane to the lens's image nodal plane, which is not always easy to locate.

Most lens DOF scales are based on the same concept. The focus spread is related to the depth of focus. Ray , 56 gives two definitions of the latter.

The first is the tolerance of the position of the image plane for which an object remains acceptably sharp; the second is that the limits of depth of focus are the image-side conjugates of the near and far limits of DOF.

With the first definition, focus spread and depth of focus are usually close in value though conceptually different. With the second definition, focus spread and depth of focus are the same.

If the detail is only slightly outside the DOF, the blur may be only barely perceptible. For a given subject magnification, f -number, and distance from the subject of the foreground or background detail, the degree of detail blur varies with the lens focal length.

For a background detail, the blur increases with focal length; for a foreground detail, the blur decreases with focal length. For a given scene, the positions of the subject, foreground, and background usually are fixed, and the distance between subject and the foreground or background remains constant regardless of the camera position; however, to maintain constant magnification, the subject distance must vary if the focal length is changed.

For small distance between the foreground or background detail, the effect of focal length is small; for large distance, the effect can be significant.

For a reasonably distant background detail, the blur disk diameter is. The magnification of the detail also varies with focal length; for a given detail, the ratio of the blur disk diameter to imaged size of the detail is independent of focal length, depending only on the detail size and its distance from the subject.

This ratio can be useful when it is important that the background be recognizable as usually is the case in evidence or surveillance photography , or unrecognizable as might be the case for a pictorial photographer using selective focus to isolate the subject from a distracting background.

As a general rule, an object is recognizable if the blur disk diameter is one-tenth to one-fifth the size of the object or smaller Williams , , [19] and unrecognizable when the blur disk diameter is the object size or greater.

The effect of focal length on background blur is illustrated in van Walree's article on Depth of field. The distance scales on most medium- and small-format lenses indicate distance from the camera's image plane.

Moreover, for many zoom lenses and internal-focusing non-zoom lenses, the location of the front nodal plane, as well as focal length, changes with subject distance.

When the subject distance is large in comparison with the lens focal length, the exact location of the front nodal plane is not critical; the distance is essentially the same whether measured from the front of the lens, the image plane, or the actual nodal plane.

The same is not true for close-up photography; at unity magnification, a slight error in the location of the front nodal plane can result in a DOF error greater than the errors from any approximations in the DOF equations.

The asymmetrical lens formulas require knowledge of the pupil magnification, which usually is not specified for medium- and small-format lenses.

The pupil magnification can be estimated by looking into the front and rear of the lens and measuring the diameters of the apparent apertures, and computing the ratio of rear diameter to front diameter Shipman , However, for many zoom lenses and internal-focusing non-zoom lenses, the pupil magnification changes with subject distance, and several measurements may be required.

The lens designer cannot restrict analysis to Gaussian optics and cannot ignore lens aberrations. However, the requirements of practical photography are less demanding than those of lens design, and despite the simplifications employed in development of most DOF formulas, these formulas have proven useful in determining camera settings that result in acceptably sharp pictures.

It should be recognized that DOF limits are not hard boundaries between sharp and unsharp, and that there is little point in determining DOF limits to a precision of many significant figures.

A symmetrical lens is illustrated at right. Setting the subject distance to the hyperfocal distance and solving for the near limit of DOF gives.

Substituting the expression for hyperfocal distance into equations 7 and 8 for the near and far limits of DOF gives. Substituting the approximate expression for hyperfocal distance into the formulas for the near and far limits of DOF gives.

As subject distance is decreased, the subject magnification increases, and eventually becomes large in comparison with the hyperfocal magnification.

Thus the effect of focal length is greatest near the hyperfocal distance, and decreases as subject distance is decreased.

Stated otherwise, for the same subject magnification and the same f -number, all focal lengths for a given image format give approximately the same DOF.

This statement is true only when the subject distance is small in comparison with the hyperfocal distance, however.

Use formulas 9 and 10 instead. It usually is more convenient to express DOF in terms of magnification. The distance is small in comparison with the hyperfocal distance, so the simplified formula.

Depth of Field DOF is the range of distance in a photo that appears to be in sharp focus Depth of field is a creative decision and one of your most important choices when composing nature photographs.

Simply put, depth-of-field is how much of a photograph is in sharp focus from front to back. We can achieve critical focus for only one plane in front of the camera, and all objects in this plane will be sharp.

In addition, there will be an area just in front of and behind this plane that will appear reasonably sharp according to the standards of sharpness required for the particular photograph and the degree of enlargement of the negative.

This total region of adequate focus represents the depth of field. If you set the camera's focus to the hyperfocal distance, your depth of field will extend from half of the hyperfocal distance to infinity—a much deeper depth of field.

Complete Digital Photography , Ben Long, Another important control for landscape photography is depth of field, the amount of sharpness in a scene, from close to the camera into the distance away from the camera.

It's sharpness in depth.

The longer exposure time with the larger camera might result in motion blur , especially with windy conditions, a moving subject, or an unsteady camera.

Adjusting the f -number to the camera format is equivalent to maintaining the same absolute aperture diameter; when set to the same absolute aperture diameters, both formats have the same DOF.

When the lens axis is perpendicular to the image plane , as is normally the case, the plane of focus POF is parallel to the image plane, and the DOF extends between parallel planes on either side of the POF.

When the lens axis is not perpendicular to the image plane, the POF is no longer parallel to the image plane; the ability to rotate the POF is known as the Scheimpflug principle.

Rotation of the POF is accomplished with camera movements tilt, a rotation of the lens about a horizontal axis, or swing, a rotation about a vertical axis.

Tilt and swing are available on most view cameras , and are also available with specific lenses on some small- and medium-format cameras.

When the POF is rotated, the near and far limits of DOF are no longer parallel; the DOF becomes wedge-shaped, with the apex of the wedge nearest the camera Merklinger , 31—32; Tillmanns , With tilt, the height of the DOF increases with distance from the camera; with swing, the width of the DOF increases with distance.

In some cases, rotating the POF can better fit the DOF to the scene, and achieve the required sharpness at a smaller f -number.

Alternatively, rotating the POF, in combination with a small f -number, can minimize the part of an image that is within the DOF. For a given subject framing and camera position, the DOF is controlled by the lens aperture diameter, which is usually specified as the f-number , the ratio of lens focal length to aperture diameter.

Reducing the aperture diameter increasing the f -number increases the DOF because the circle of confusion is shrunk directly and indirectly by reducing the light hitting the outside of the lens which is focused to a different point than light hitting the inside of the lens due to spherical aberration caused by the construction of the lens; [7] however, it also reduces the amount of light transmitted, and increases diffraction , placing a practical limit on the extent to which DOF can be increased by reducing the aperture diameter.

Motion pictures make only limited use of this control; to produce a consistent image quality from shot to shot, cinematographers usually choose a single aperture setting for interiors and another for exteriors, and adjust exposure through the use of camera filters or light levels.

Aperture settings are adjusted more frequently in still photography, where variations in depth of field are used to produce a variety of special effects.

The advent of digital technology in photography has provided additional means of controlling the extent of image sharpness; some methods allow extended DOF that would be impossible with traditional techniques, and some allow the DOF to be determined after the image is made.

Focus stacking is a digital image processing technique which combines multiple images taken at different focal distances to give a resulting image with a greater depth of field than any of the individual source images.

Getting sufficient depth of field can be particularly challenging in macro photography. The images to the right illustrate the extended DOF that can be achieved by combining multiple images.

Wavefront coding is a method that convolves rays in such a way that it provides an image where fields are in focus simultaneously with all planes out of focus by a constant amount.

A plenoptic camera uses a microlens array to capture 4D light field information about a scene. Colour apodization is a technique combining a modified lens design with image processing to achieve an increased depth of field.

The lens is modified such that each colour channel has a different lens aperture. Therefore, the blue channel will have a greater depth of field than the other colours.

The image processing identifies blurred regions in the red and green channels and in these regions copies the sharper edge data from the blue channel.

The result is an image that combines the best features from the different f -numbers, Kay In , Nokia implemented DOF control in some of its high-end smartphones , called Refocus, which can change a picture's depth of field after the picture is taken.

It works best when there are close-up and distant objects in the frame. If the camera position and image framing i.

Because of diffraction, however, this isn't really true. Once a lens is stopped down to where most aberrations are well corrected, stopping down further will decrease sharpness in the plane of focus.

At the DOF limits, however, further stopping down decreases the size of the defocus blur spot, and the overall sharpness may still increase.

Eventually, the defocus blur spot becomes negligibly small, and further stopping down serves only to decrease sharpness even at DOF limits Gibson , For general photography, diffraction at DOF limits typically becomes significant only at fairly large f -numbers; because large f -numbers typically require long exposure times, motion blur may cause greater loss of sharpness than the loss from diffraction.

That lens includes distance scales in feet and meters; when a marked distance is set opposite the large white index mark, the focus is set to that distance.

The DOF scale below the distance scales includes markings on either side of the index that correspond to f -numbers. When the lens is set to a given f -number, the DOF extends between the distances that align with the f -number markings.

Conversely, the required focus and f -number can be determined from the desired DOF limits by locating the near and far DOF limits on the lens distance scale and setting focus so that the index mark is centered between the near and far distance marks.

The required f -number is determined by finding the markings on the DOF scale that are closest to the near and far distance marks Ray , The focus so determined would be about 1.

The DOF limits can be determined visually, by focusing on the farthest object to be within the DOF and noting the distance mark on the lens distance scale, and repeating the process for the nearest object to be within the DOF.

Using other distances for DOF limits requires visual interpolation between marked distances. Since the distance scale is nonlinear, accurate interpolation can be difficult.

In most cases, English and metric distance markings are not coincident, so using both scales to note focused distances can sometimes lessen the need for interpolation.

Many autofocus lenses have smaller distance and DOF scales and fewer markings than do comparable manual-focus lenses, so that determining focus and f -number from the scales on an autofocus lens may be more difficult than with a comparable manual-focus lens.

In most cases, determining these settings using the lens DOF scales on an autofocus lens requires that the lens or camera body be set to manual focus.

On a view camera, the focus and f -number can be obtained by measuring the focus spread and performing simple calculations. The procedure is described in more detail in the section Focus and f -number from DOF limits.

Some view cameras include DOF calculators that indicate focus and f -number without the need for any calculations by the photographer Tillmanns , 67—68; Ray , — The hyperfocal distance is the nearest focal distance at which the DOF extends to infinity; focusing the camera at the hyperfocal distance results in the largest possible depth of field for a given f -number Ray , Focusing beyond the hyperfocal distance does not increase the far DOF which already extends to infinity , but it does decrease the DOF in front of the subject, decreasing the total DOF.

Some photographers consider this wasting DOF; however, see Object field methods above for a rationale for doing so.

Focusing on the hyperfocal distance is a special case of zone focusing in which the far limit of DOF is at infinity. If the lens includes a DOF scale, the hyperfocal distance can be set by aligning the infinity mark on the distance scale with the mark on the DOF scale corresponding to the f -number to which the lens is set.

Some cameras have their hyperfocal distance marked on the focus dial. For example, on the Minox LX focusing dial there is a red dot between 2 m and infinity; when the lens is set at the red dot, that is, focused at the hyperfocal distance, the depth of field stretches from 2 m to infinity.

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 , 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.

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.

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. When the subject is at the hyperfocal distance or beyond, the far DOF is infinite, so the ratio is 1: For large apertures at typical portrait distances, the ratio is still close to 1: As a lens is stopped down, the defocus blur at the DOF limits decreases but diffraction blur increases.

The presence of these two opposing factors implies a point at which the combined blur spot is minimized Gibson , 64 ; at that point, the f -number is optimal for image sharpness.

If the final image is viewed under normal conditions e. But this may not be true if the final image is viewed under more demanding conditions, e.

Hansma also suggests that the final-image size may not be known when a photograph is taken, and obtaining the maximum practicable sharpness allows the decision to make a large final image to be made at a later time.

Hansma and Peterson have discussed determining the combined effects of defocus and diffraction using a root-square combination of the individual blur spots.

Hansma's approach determines the f -number that will give the maximum possible sharpness; Peterson's approach determines the minimum f -number that will give the desired sharpness in the final image, and yields a maximum focus spread for which the desired sharpness can be achieved.

Gibson , 64 gives a similar discussion, additionally considering blurring effects of camera lens aberrations, enlarging lens diffraction and aberrations, the negative emulsion, and the printing paper.

Hopkins , Stokseth , and Williams and Becklund have discussed the combined effects using the modulation transfer function. In semiconductor photolithography applications, depth of field is extremely important as integrated circuit layout features must be printed with high accuracy at extremely small size.

The difficulty is that the wafer surface is not perfectly flat, but may vary by several micrometres. Even this small variation causes some distortion in the projected image, and results in unwanted variations in the resulting pattern.

Thus photolithography engineers take extreme measures to maximize the optical depth of field of the photolithography equipment.

To minimize this distortion further, semiconductor manufacturers may use chemical mechanical polishing to make the wafer surface even flatter before lithographic patterning.

A person may sometimes experience better vision in daylight than at night because of an increased depth of field due to constriction of the pupil i.

The basis of these formulas is given in the section Derivation of the DOF formulae ; [17] refer to the diagram in that section for illustration of the quantities discussed below.

Thus, for a given image format, depth of field is determined by three factors: For close-up work, the hyperfocal distance has little applicability, and it usually is more convenient to express DOF in terms of image magnification.

In other words, for the same subject magnification, at the same f -number, all focal lengths used on a given image format give approximately the same DOF.

The discussion thus far has assumed a symmetrical lens for which the entrance and exit pupils coincide with the front and rear nodal planes , and for which the pupil magnification the ratio of exit pupil diameter to that of the entrance pupil [18] is unity.

Although this assumption usually is reasonable for large-format lenses, it often is invalid for medium- and small-format lenses. When the pupil magnification is unity, this equation reduces to that for a symmetrical lens.

Except for close-up and macro photography, the effect of lens asymmetry is minimal. At unity magnification, however, the errors from neglecting the pupil magnification can be significant.

If only working f -number is directly available, the following formula can be used instead:. When the subject distance is large in comparison with the lens focal length, the required f -number is.

In practice, these settings usually are determined on the image side of the lens, using measurements on the bed or rail with a view camera, or using lens DOF scales on manual-focus lenses for small- and medium-format cameras.

In practical terms, focus is set to halfway between the near and far image distances. The required f -number is. The image distances are measured from the camera's image plane to the lens's image nodal plane, which is not always easy to locate.

Most lens DOF scales are based on the same concept. The focus spread is related to the depth of focus. Ray , 56 gives two definitions of the latter.

The first is the tolerance of the position of the image plane for which an object remains acceptably sharp; the second is that the limits of depth of focus are the image-side conjugates of the near and far limits of DOF.

With the first definition, focus spread and depth of focus are usually close in value though conceptually different. With the second definition, focus spread and depth of focus are the same.

If the detail is only slightly outside the DOF, the blur may be only barely perceptible. For a given subject magnification, f -number, and distance from the subject of the foreground or background detail, the degree of detail blur varies with the lens focal length.

For a background detail, the blur increases with focal length; for a foreground detail, the blur decreases with focal length.

For a given scene, the positions of the subject, foreground, and background usually are fixed, and the distance between subject and the foreground or background remains constant regardless of the camera position; however, to maintain constant magnification, the subject distance must vary if the focal length is changed.

For small distance between the foreground or background detail, the effect of focal length is small; for large distance, the effect can be significant.

For a reasonably distant background detail, the blur disk diameter is. The magnification of the detail also varies with focal length; for a given detail, the ratio of the blur disk diameter to imaged size of the detail is independent of focal length, depending only on the detail size and its distance from the subject.

This ratio can be useful when it is important that the background be recognizable as usually is the case in evidence or surveillance photography , or unrecognizable as might be the case for a pictorial photographer using selective focus to isolate the subject from a distracting background.

As a general rule, an object is recognizable if the blur disk diameter is one-tenth to one-fifth the size of the object or smaller Williams , , [19] and unrecognizable when the blur disk diameter is the object size or greater.

The effect of focal length on background blur is illustrated in van Walree's article on Depth of field. The distance scales on most medium- and small-format lenses indicate distance from the camera's image plane.

Moreover, for many zoom lenses and internal-focusing non-zoom lenses, the location of the front nodal plane, as well as focal length, changes with subject distance.

When the subject distance is large in comparison with the lens focal length, the exact location of the front nodal plane is not critical; the distance is essentially the same whether measured from the front of the lens, the image plane, or the actual nodal plane.

The same is not true for close-up photography; at unity magnification, a slight error in the location of the front nodal plane can result in a DOF error greater than the errors from any approximations in the DOF equations.

The asymmetrical lens formulas require knowledge of the pupil magnification, which usually is not specified for medium- and small-format lenses.

The pupil magnification can be estimated by looking into the front and rear of the lens and measuring the diameters of the apparent apertures, and computing the ratio of rear diameter to front diameter Shipman , However, for many zoom lenses and internal-focusing non-zoom lenses, the pupil magnification changes with subject distance, and several measurements may be required.

The lens designer cannot restrict analysis to Gaussian optics and cannot ignore lens aberrations. However, the requirements of practical photography are less demanding than those of lens design, and despite the simplifications employed in development of most DOF formulas, these formulas have proven useful in determining camera settings that result in acceptably sharp pictures.

It should be recognized that DOF limits are not hard boundaries between sharp and unsharp, and that there is little point in determining DOF limits to a precision of many significant figures.

A symmetrical lens is illustrated at right. Setting the subject distance to the hyperfocal distance and solving for the near limit of DOF gives.

Substituting the expression for hyperfocal distance into equations 7 and 8 for the near and far limits of DOF gives.

It's sharpness in depth. Depth of Field Definition Hyperfocal, near, and far distances are calculated using these equations. Circles of confusion for digital cameras are listed here.

Depth of Field Calculator. Camera, film format, or circle of confusion. Use the actual focal length of the lens for depth of field calculations.

The calculator will automatically adjust for any "focal length multiplier" or "field of view crop" for the selected camera. Focal lengths of digital camera lenses are listed here.

Focus at the subject distance, 10 ft. Focus at the hyperfocal distance,

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