DoF Reference Manual (Windows and Android)

DoF Reference Manual (Windows and Android)
DoF 4.0 – A Depth of Field Calculator
Last updated: 23-Jan-2015
Introduction
When you focus a camera lens at some distance and take a photograph, the further subjects are from the focus point,
the blurrier they look.
Depth of field is the range of subject distances that are acceptably sharp. It varies with aperture and focal length,
distance at which the lens is focused, and the circle of confusion – a measure of how much blurring is acceptable in a
sharp image. The tricky part is defining what acceptable means. Sharpness is not an inherent quality as it depends
heavily on the magnification at which an image is viewed. When viewed from the same distance, a smaller version of the
same image will look sharper than a larger one. Similarly, an image that looks sharp as a 4x6" print may look decidedly
less so at 16x20".
All other things being equal, the range of in-focus distances increases with shorter lens focal lengths, smaller apertures,
the farther away you focus, and the larger the circle of confusion. Conversely, longer lenses, wider apertures, closer
focus, and a smaller circle of confusion make for a narrower depth of field.
Sometimes focus blur is undesirable, and sometimes it’s an intentional creative choice. Either way, you need to
understand depth of field to achieve predictable results.
What is DoF?
DoF is an advanced depth of field calculator available for both Windows and Android.
What DoF Does
Even if your camera has a depth of field preview button, the viewfinder image is just too small to judge critical sharpness.
Only when you open images on your computer and zoom in (or when you examine a film negative or positive with a
powerful magnifier) can you see what is really sharp and what isn’t, and by then it’s usually too late to do anything about
it. This is the kind of problem DoF is designed to help you avoid.
DoF's camera-like interface helps you develop an intuitive understanding of depth of field.
Here are some of the many questions DoF can answer about depth of field:

What range of subject distances are in focus for a given camera, lens, f stop and focus distance?
This is the classical question addressed by most depth of field calculators. DoF computes the near and far focus
limits as well as the hyperfocal distance – the closest distance you can focus at while keeping distant subjects sharp,
taking both focus and diffraction blur into account.

What f stop makes subjects in a given distance range as sharp as possible? How sharp?
Suppose you want to photograph a scene that includes a known range of camera-to-subject distances. If the
distance range is narrow enough, you can use a large aperture to reduce diffraction and still get a sharp image. For
wider ranges, you can reduce focus blur by stopping down to increase depth of field, but this increases diffraction
blur, so what is the best f stop to use? It turns out that when focus blur and diffraction blur are equal, the two effects
balance out and you get the sharpest possible image. DoF can calculate this ideal f stop and show you how much the
image is blurred both inside and outside the range.

How does blur vary with subject distance for a given f stop?
DoF displays a visual representation of blur as a function of distance. This helps you previsualize how sharp in-focus
areas are and how blurry out-of-focus areas are. It can determine how much the background will be blurred when
you focus on a foreground subject and vice versa.

Where should I focus to make a range of distances as sharp as possible?
Suppose you have two subjects at different distances from the camera that define a range you want to be as sharp
as possible. The best distance at which to focus is the one that blurs both the near and far subjects equally. DoF can
calculate this distance exactly. The rule of thumb of focusing 1/3 of the way into the range is almost always
inaccurate.

Using focus stacking, how many images, focused at what distances do I need to produce a sharp image?
Focus stacking is a software post-processing technique that combines multiple images of the same scene shot with
different focus points to create a composite with a wider depth of field than any of the individual images. DoF can
calculate the number of images you need to shoot, the best f stop to use, and the distances at which to focus each
image to produce a sharp focus stacking result.

What is the depth of field for macro photography?
Normal depth of field equations work for subjects far from the camera but become unworkable when the subject is
too close. When this happens, a different calculation based on image magnification is more useful. DoF can
calculate magnification from the width of the field of view (easily measured by photographing a ruler placed at the
subject distance) and in turn compute the depth of field for macro photography.
Quantifying Sharpness - The Circle of Confusion
To compute depth of field, DoF needs a value for the diameter of the circle of confusion (sometimes abbreviated CoC)
which is in turn a measure of the maximum acceptable blur in a sharp image. Since the transition from sharp to blurry is
gradual, the size of the circle of confusion is inherently imprecise. More importantly, percieved sharpness varies
according to how much the image is magnified when you view it and other viewing conditions. For example, an image
that looks sharp printed at postcard size may not be sharp at all when printed as a 16x20 and viewed up close. DoF lets
you choose between two basic methods to calculate CoC size based on two methods for judging whether an image is
sharp or not:
The Sharp Image method
Viewing the image on-screen at a magnification of 100% or greater (or examining a film positive or negative with a
high-power loupe) – this makes even the most minor blurring apparent. Using Sharp Image calculates the circle of
confusion as the size of the smallest resolvable detail measured at the camera sensor (or film plane). Calculating
depth of field using this method helps you produce images as sharp as your camera can capture. Reducing the circle
of confusion beyond this point does not make images significantly sharper, but it does unnecessarily reduce the
calculated depth of field.
The Sharp Print method
Viewing a standard size print at a standard distance – this method is based on making sure a print of the image looks
sharp to a standard observer under specific conditions. Of course the print size matters, as well as how closely you
examine it, and how good your eyesight is. The standard definition of this method is based on an 8x12 inch print
viewed from about 18 inches by an observer with normal eyesight, the assumption being that larger prints are viewed
from a proportionally greater difference. If you want to use a different print size or viewing distance, DoF lets you
adjust the circle of confusion accordingly.
By international convention, the Sharp Print method (or a minor variant of it) is used by camera manufacturers when
they engrave depth of field marks on lens barrels, but the choice of circle of confusion (roughly 0.03mm for 35mm
film format) dates back to a time when film emulsions had much less resolution than present day film or digital
sensors. While this method remains somewhat valid for making 8x10 or 8x12 prints, it generally falls far short of
producing truly sharp film or digital images using today's cameras or films.
While DoF can compute the circle of confusion using either the Sharp Image or the Sharp Print methods, they often
produce very different results for depth of field. For example, a Nikon D810 has a 35mm wide sensor that resolves 7360
pixels across its larger dimension. This computes out to a circle of confusion of about 0.01mm for the Sharp Image
method and a value for Sharp Print of about 0.03mm which is roughly 3 times larger! Photographs taken based on the
larger circle of confusion can look like mush when viewing individual pixels and still produce acceptably sharp 8x12 inch
prints viewed from 18 inches away. Thus, if all you want is prints that look sharp from a distance, you don't need nearly
the resolution the camera can deliver. In other words, it is OK if the digital image is blurry as long as it is reproduced at a
size where that blur is invisible.
On the other hand, having invested in a camera with high resolution and quality optics, if you want to get the sharpest
images you can, you should use the Sharp Image method and accept the fact that your depth of field is actually much
narrower than you may have thought. If you ever plan to crop your images before printing or make large prints of your
images and want them to look good up close, you will need extra sharpness anyway. Sometimes you need more depth of
field than this method allows and you need to make a deliberate trade-off.
DoF represents blur as a number: a blur of 1.0 or less means combined diffraction and focus blur is less than or equal to
the circle of confusion for the current camera and thus that the image should be sharp according to the criteria you
specified when you created the camera setting. The larger the blur value, the softer the image.
Just to make things even more complicated, it turns out the eye is much more sensitive to blur in high contrast subjects
with sharp edges like black text on a white background or a photo of a skyscraper with lots of dark windows against light
concrete. This is why such subjects are often used for resolution test charts. When photographing high contrast scenes
depth of field should be calculated with a smaller circle of confusion (a smaller blur value). Conversely, low contrast
subjects can tolerate a little blur and depth of field may be calculated with a larger circle of confusion (a larger blur value).
If you have been using the Sharp Print method to calculate depth of field and are getting images that are not critically
sharp when you examine them closely, try using Sharp Image before blaming your equipment or technique. Personally, I
mostly use the Sharp Image method and then decide on a case-by-case basis whether to accept blur values higher than
1.0 if I need extra depth of field. At blur level 2.0 images are still quite sharp – only above 3.0 or so do images start to
deteriorate seriously. To get a sense of what different levels of blur look like, see Appendix B3 which illustrates test target
images intentionally defocused so as to introduce calibrated amounts of blur.
Depth of Field and Magnification
Magnification is defined as the ratio of the size of the image of a subject the camera is focused on to the size of the
actual subject. Photographs taken at the same magnification (i.e. where images of the same subject are the same size at
the sensor or film plane) have the same depth of field, regardless of the lens focal length. To get the same magnification
with a longer lens you of course need to move further away from the subject so the perspective is altered. For example,
shooting a subject 10 feet away with a 50mm lens gives almost exactly the same depth of field as shooting the same
subject 20 feet away with a 100mm lens.
Diffraction
Diffraction is a quantum effect resulting from the wave nature of light as it passes through a small aperture. While
diffraction does not affect depth of field directly, it does limit the sharpness you can achieve at a given f stop. Since
diffraction blur increases for smaller apertures, and focus blur increases for larger apertures, there is an optimal f stop
that produces the smallest combined blur and thus the sharpest image for any given range of distances. Unlike focus
blur, diffraction blur does not depend of subject distance and thus affects the entire image uniformly.
The amount of diffraction blur is proportional to the wavelength of light entering the lens. By convention, 550nm green
light is used to calculate diffraction blur since the eye is most sensitive to this color and because green is in the middle of
the range of visible wavelengths as shown below:
Red light causes about 20% more diffraction than green light and blue/violet light about 20% less. This can be significant
for IR or UV photography. DoF lets you customize the wavelength used to calculate diffraction if you need to adjust the
value for special situations.
Why Other Depth of Field Calculators Are Misleading
There are two reasons depth of field calculated the standard way may not lead to critically sharp images.
Ignoring diffraction
Diffraction effects can be important, especially for newer digital cameras with small, high resolution sensors. Even at
larger apertures, diffraction blur adds to out-of-focus blur and narrows depth of field to some extent. At smaller
apertures, diffraction blur can easily exceed the circle of confusion and the image won't be acceptably sharp
anywhere.
Ignoring image resolution
The standard method for deciding if an image is sharp is based on viewing a print of the image, not by examining the
digital image (or film) itself. Modern digital cameras can resolve a lot more detail than you can see in an 8x12 print
seen from a normal viewing distance.
Both of these factors can lead you to overestimate depth of field and consequently your images will not be as sharp as
possible, especially near the endpoints of the depth of field range. While you can configure DoF to calculate depth of field
in the conventional manner, it can also calculate depth of field using more precise methods that account for both
diffraction and sensor resolution.
The Problem with High Resolution Digital Cameras
To make the most of the high resolution sensor in your digital camera and get really sharp images, you should use the
Sharp Image method and reconcile yourself to the fact that small apertures cause diffraction blur so the sharpest images
require larger apertures which then lead to a relatively narrow depth of field.
For example, using a Nikon D810 with a 50mm lens, diffraction reaches sensor resolution at around f/8 using the Sharp
Image method. At f/8, the hyperfocal distance is about 100 ft. with a corresponding near focus of about 50 ft. Stopping
down to get more depth of field blurs the entire image from diffraction. By contrast, using the Sharp Print method,
diffraction is not a limiting factor even at f/22 which corresponds to a hyperfocal distance of about 12 ft. and a near focus
of 6 ft. While you can make prints that look good from a distance when shooting at f/22, images shot at f/8 will be
significantly sharper when examined closely.
Focusing Strategies for Sharp Images
There are several strategies for focusing a camera on a scene containing visual elements at a wide range of distances,
such as a mountain in the background with flowers or foliage in the foreground.
Focus between the near and far distance
Assuming the near subject distance is Dn and the far subject distance is Df, if you focus at a distance of
2DfDn/(Df+Dn), subjects at both distances are equally blurred. If Df is ∞, focus at the hyperfocal distance. This is the
standard method – it produces images in which subjects at the intermediate distance are optimally sharp while there
is an acceptable loss of detail (as defined by the circle of confusion) at the near and far limits.
Focus at the far distance
This method, advocated by Harold Merklinger and others, suggests you are better off focusing at or near the far
distance limit so distant objects appear sharper at the expense of a softer foreground. The rationale is that subjects
in the distance appear smaller and will look blurrier if they are not critically sharp, and that viewers tolerate blurring in
the foreground more than in the background.
Using a tilt and shift lens (or a view camera that allows tilt and shift adjustments)
This can extend depth of field in some situations by more closely aligning the image plane with the subject, but DoF
does not calculate depth of field for this special type of lens.
Focus Stacking
Another way to get really sharp images with a very wide depth of field – and this usually only works well for more or
less stationary subjects – is focus stacking, a technique in which you take multiple photographs of a scene while
varying the focus incrementally. The images are then combined afterwards using software that combines the
sharpest parts of each one to create a composite image with a depth of field much wider than any of the individual
images. Two popular examples of commercial focus stacking programs are Helicon Focus and Zerene Stacker,
although there are many others. While focus stacking has long been used by macro and micro photographers,
increasingly it is becoming an important tool for high quality landscape photography.
Unfortunately, focus stacking has limitations – for example, if the subject moves while you are taking the series of
photos, the stacking software may have trouble merging the images cleanly and they will either require a lot of
manual touch-up or may ultimately be unusable. When it works however, the results can be spectacular. If focus
stacking is not an option, you have no choice but to stop down to the best f stop and accept some blur.
Distance Scale and Lens Markings
The distance scale DoF displays is graduated like the markings on a lens barrel, being much more compressed for
distant subjects than for closer ones. The scale is created in such a way that the depth of field limit markers stay the
same distance apart as you vary subject distance, and are equally spaced on either side of the focus distance. Equal
distances along this harmonic distance scale correspond to equal rotations of the lens barrel when you use manual
focus.
Useful Tips:
You can always find the best focus point bewteen a near and a far subject by rotating the focus ring half way between the
focus points for the two subjects.
For focus stacking, intermediate focus points correspond to equal rotations of the lens barrel. Similarly for a view camera,
the best location for the front standard is halfway between the locations that produce sharp focus for the near and far
ends of the range.
How Blur Varies with Distance
If you use a certain lens and f stop and focus at a given distance, how blurry are subjects at other distances? DoF
displays blur as a function of distance, but the following graph illustrates how this works. It represents blur at different
distances for a 45mm lens on an Olympus OM-D EM-1 set to f/8 and focused at a point 5 feet from the camera.
The graph shows the amount of blur in millimeters at the image plane. The red line represents focus blur, the blue line
diffraction blur and the black line combined diffraction and focus blur. The gray line indicates the circle of confusion.
The points where the red line crosses the gray line represent depth of field, ignoring diffraction. Since the black line does
not cross the gray line (because the f stop is above the diffraction limit of f/5.6 for this camera), there is no distance at
which the image is critically sharp. Nonetheless, the image stays fairly sharp from about 4.5 to 5.5 feet.
The graph shows that blur increases much faster on the near side of the focus point than for distant subjects. We
understand this intuitively when we move closer to a window screen to blur out its effect and let us see distant objects
more clearly. Blur becomes infinite at subject distances less than or equal to the lens focal length.
Best F Stop for a Given Depth of Field
If you want to capture a specific range of distances, what f stop produces the sharpest image? DoF can find the f stop
that produces the least combined diffraction and focus blur at the endpoints of the range.
To see how this works, consider a 45mm lens on an Olympus OM-D EM-1 (Sharp Image method), focused at a distance
of 5 feet. The following graph illustrates how blurry a subject at 4.5 feet appears as you vary the f stop.
This graph measures the amount of blur in millimeters at the image plane. The blue line is diffraction blur which
increases with f stop. The red line is focus blur which decreases with f stop. The black line is combined blur (computed
as the geometric mean of diffraction and focus blur) which reaches its lowest point when diffraction blur and focus blur
are equal. The gray line represents the circle of confusion for the camera, so in this case even at the best possible f stop,
the image is not as sharp as the camera can capture, but it is the best compromise. Generally the image stays about as
sharp for about one f stop on either side of the optimal value so it doesn't matter much if you are a little off, but beyond
that point it starts to get less sharp fairly quickly.
Strategies for Selective Focus
Selective focus refers to blurring parts of an image intentionally, usually to remove a distracting background, create a
sense of depth, or bring attention to the sharper parts of the image. This can be achieved by using a shallow depth of
field or by digital post-processing.
To reduce depth of field, use a larger lens aperture.
You also have the option of selectively blurring an image with your computer, although this is likely to involve a
painstaking masking process.
Selective Focus Achieved by Digital Posprocessing
Range Finders
Knowing the range of in-focus distances is not particularly useful unless you have a way to measure how far subjects are
from the camera. Since it is difficult to estimate distances accurately by eye, a range finder can be a useful aid in the
field. Laser range finders work by projecting a laser beam onto the subject and observing the reflected light coming back.
Some use visible red lasers while others use invisible IR lasers.
Laser range finders designed for building construction are small, safe, very accurate and not terribly expensive. They use
visible lasers that project a red dot on the subject, but you need to be able to see the dot to know what you are
measuring. This works indoors or at short distances, but outdoors in bright sunlight it can be nearly impossible to see the
red dot. The Leica DISTO E7500i works better for outdoor photography as it is both very accurate and has a feature they
call "point finder" that displays a zoomable image on its screen with a crosshair at the spot it is measuring so you don't
have to be able to see the red dot to get a reading.
IR laser rangefinders designed for forestry, hunting or golf are usually integrated into a monocular and work very well
outside. While they can measure out to great distances, they are usually only accurate to about a yard and cannot
measure short distances at all. One exception is the new Laser Technology TruPulse 200X which measures both short
and long distances to within a few inches – unfortunately it is a little bulky and rather expensive.
Leica 7500i
TruPulse 200X
Accuracy
Many factors other than lack of focus and diffraction contribute to image blur, including lens aberrations, camera or
subject motion during the exposure, sensor noise, antialiasing filters, sensor dithering patterns, lack of film flatness and
so on. DoF ignores all of these. Furthermore, sharpness is ultimately subjective and the depth of field equations are
approximate, so DoF results should not be considered precise. Also, subject distances are measured from the front
nodal point of the lens which is difficult to locate accurately. This error is more significant for subjects close to the lens, in
which case you should switch to the macro depth of field mode.
Using DoF
Windows
Android
The Top of the Window
The Window caption displays the name of the currently selected camera.
Camera Menu Button
Click this button to edit camera properties, configure a new camera, or select a different camera.
Mode Tool Bar
Click this button to select Depth of Field mode – you enter a lens focal length, f stop, and subject distance and
DoF computes the depth of field.
Click this button to select Best f Stop mode – you enter a lens focal length and range of subject distances and
DoF computes the f stop that produces the least blur over that range.
Click this button to select Focus Stacking mode – you enter a lens focal length, a number of images, and a range
of subject distances and DoF computes the f stop that produces the least blur over that range and the best
distances at which to focus each image.
Click this button to select Blur mode – you enter a lens focal length, f stop, focus distance and subject distance
and DoF computes the amount of blur at the subject distance.
Click this button to select Macro mode – you enter a field of view and an f stop and DoF computes the depth of
field.
Command Bar
Click this button to select distance units (mm/cm/in/ft/yd/m) – there is a separate setting
for macro mode.
Click this button to display additional details for the current mode. Click the button again or click elsewhere on the
screen to restore the normal display.
Click this button for help commands.
About DoF
Quick Start
Reference Manual
Display About box
Display Quick Start Manual
Display Reference Manual (this document)
Reset Scales
Use this command to reset the focal length, aperture, distance and blur scales to default
values in case you manage to accidentally scroll or zoom them out of range.
Snap Toggle
Click this button to toggle Snap on or off. When Snap is on, focal length, f stop and distance values are adjusted
to round numbers which makes it easier to select exact values such as 15.0. When Snap is off, no rounding is
performed.
Windows - The DoF window is resizable – scales are automatically lengthened or shortened to fill the height of the
window, and the text size is increased or decreased to fill the window width.
Android - The text size is automatically scaled according to the device resolution.
Focal Length Scale
Use the focal length scale to set the lens focal length in millimeters. Select the actual focal length
and not the 35mm equivalent (unless you have specified Enter 35mm equivalent in the Camera
Dialog).
The red triangle marks the current setting whose value is also displayed at the top of the scale.
Drag the scale to change the focal length – the red marker stays fixed in the center.
Windows - Dragging the scale up or down with the right mouse button down zooms the scale so it
becomes more or less compressed.
Android - Pinch to zoom the scale so it becomes more or less compressed.
If you are using a teleconverter, click the teleconverter button above the focal length scale and
select the desired teleconverter magnification factor (1.4X or 2X). The teleconverter setting
automatically adjusts the f stop so there is no need to do so yourself – just enter the aperture
value indicated on the lens dial. For example, a 300mm lens at f/16 with a 2X teleconverter is
automatically treated as a 600mm lens at f/32.
Aperture Scale
Use the aperture scale to set the f stop in Depth of Field, Blur or Macro mode. In the other modes,
the f stop is calculated for you. If the triangle is white, this means the value is set by the program
and cannot be modified. If the triangle is red, you can drag the marker to set the f stop manually.
Select the f stop as marked on the lens – do not attempt to correct for extension due to macro
focusing as this is already taken into account by the formulas used to compute the depth of field.
The color of the f stop label indicates how much diffraction blur occurs at the corresponding
aperture. White means 1.0 or less.
F stop values on cameras are approximate. For f stops that are not a power of 2, the displayed
number may look a little off, but it is actually the precise f stop value.
Select whether you want to subdivide the scale in half or third stop increments by clicking the
button at the top the aperture scale and selecting half or third stop increments from the menu.
Distance Scale
The numbers down the right side are subject distances in the current units.
The numbers down the left side are blur amounts. A blur of 1.0 means
combined diffraction and focus blur is equal to the circle of confusion for the
current camera and thus the image should be sharp according to the criteria
you set up when you created the current camera setting. The larger the blur
value, the softer the image. To see examples of how soft an image looks at
different blur levels, see Appendix B3.
The middle part of the distance scale consists of an image that shows
combined focus and diffraction blur, color coded to indicate what distances are
blurred the most. The width of the line is proportional to the amount of blur –
you can think of it as the blurred image of a very narrow vertical line.
A green line marks the focus distance. The blur number next to the green line
is the amount of diffraction blur since focus blur is zero at this distance.
Red lines mark the near and far focus limits, taking both diffraction and focus
blur into account, so they indicate the distances at which the combined blur is
equal to the blur level as set on the blur scale. The red lines may not be visible
if the f stop is too large.
A blue-green line marks the hyperfocal distance – the closest distance at
which subjects at infinity are acceptably sharp. The blue line may not be visible
if the hyperfocal distance is off-scale.
In this example, diffraction blur is 0.71. Subjects at distances between the two
blur values of 1 (as indicated by the two red lines) will be critically sharp, taking
both focus and diffraction blur into account. If the selected f stop is large
enough to push diffraction blur above the blur level, then there are no
distances at which subjects are critically sharp and the red lines disappear.
To see the distance range for a different blur level, set the Blur scale (see
below) to the desired value. The red lines will then move either closer together
or farther apart to indicate the change in depth of field range.
If there is a red or green triangle, you can drag it to adjust its distance value. If
there is only a line and no triangle, the value is computed automatically and
cannot be dragged.
In Depth of Field or Macro mode, click anywhere on the distance scale to set
the focus distance.
In Best f Stop or Focus Stacking mode, drag either red line to set the camera
to subject distance range.
In Blur mode, drag the green line to set the focus distance and drag the red
line to set the subject distance.
Windows - Dragging the right side of the distance scale up or down with the
right mouse button down zooms the scale so it becomes more or less
compressed.
Android - Pinch to zoom the right side of the distance scale so it becomes
more or less compressed.
In Focus Stacking mode, white lines mark the locations of any intermediate focus
points. Drag either red line to set the camera to subject distance range.
Increase or decrease the number of focus points by clicking
or
. The more
intermediate focus points you add, the more tightly you can limit blurring of the entire
range. The Blur scale readout shows you the worst case blur between the focus limits.
Blur Scale
The color coded blur scale shows the amount of combined diffraction and focus blur at the near
and far distance limits.
A blur of 1.0 means combined diffraction and focus blur is equal to the circle of confusion for the
current camera and thus that the image should be sharp according to the criteria you specified
when you created the camera setting. The larger the blur value, the softer the image. To see
examples of how soft an image looks at different blur levels, see Appendix B3.
If you selected the Sharp Image method of calculating the circle of confusion, setting the blur value
to 1.0 guarantees images about as sharp as your camera can capture, but the resulting depth of
field may be impractically narrow. Increasing the blur value provides more depth of field at the
expense of a softer image.
Making a deliberate tradeoff of a limited amount of blur for additional depth of field may be
required in some situations. In Depth of Field or Macro mode, if the current f stop exceeds the
diffraction limit, a blur level of 1.0 will result in no depth of field at all, so increasing the blur level in
this case will be necessary.
In Depth of field or Macro modes, you can drag the blur scale up or down to set the acceptable
blur level – the red marker remains centered.
Windows - Dragging the scale up or down with the right mouse button down zooms the scale so it
becomes more or less compressed.
Android - Pinch to zoom the scale so it becomes more or less compressed.
In Best f stop mode, the blur scale is automatically set to the amount of blur at the focus limits. In
this case it is a read-out only and cannot be adjusted.
In Blur mode, the blur scale is automatically set to the amount of blur at the subject distance. In
this case it is a read-out only and cannot be adjusted.
In Focus stacking mode, the blur scale is automatically set to the amount of blur at the most outor-focus point between the focus limits. In this case it is a read-out only and cannot be adjusted.
Blur Color Coding
Blur levels are color coded according to the following scheme:
Blur Level
Color
less than 1
between 1 and 2
between 2 and 10
between 10 and 20
between 20 and 40
above 40
White
Gradual transition from White to Yellow
Gradual transition from Yellow to Red
Gradual transition from Red to Magenta
Gradual transition from Magenta to Blue
Blue
Field of View Scale
In Macro mode, a field of view scale replaces the lens focal length scale.
Use the field of view scale to set the field of view in the current units, as measured by
photographing a ruler at the desired subject distance.
The red triangle marks the current setting which is also displayed at the top of the scale.
Drag the scale to set the field of view – the red marker always stays in the center
Windows - Dragging the scale up or down with the right mouse button down zooms the scale so it
becomes more or less compressed.
Android - Pinch to zoom the scale so it becomes more or less compressed.
Measuring Subject Distances
Subject distance is measured along the direction the camera is pointing. If the subject is off-center, you need to measure
the distance to the plane passing through the subject perpendicular to the direction the camera is aimed.
Camera-to-subject distance is measured from the front nodal point of the lens which is normally located somewhere near
the center of the front element or perhaps a little closer to the film plane. Since lens manufacturers rarely if ever mark this
point on the lens, in practice you can just measure from the front element which is a conservative assumption. Unless
you are doing macro photography, it does not make much difference what part of the camera you measure from since
any error will be a negligible fraction of the subject distance. Distance markings on lens barrels are measured from the
film plane and not the front of the lens so they may not correspond exactly to the numbers used by DoF.
Camera Settings
When computing depth of field, one important parameter is the size of the circle of confusion. When you select the
camera to use with DoF, what you are really selecting is what value to use for the circle of confusion, based on
characteristics of the camera and various sharpness criteria.
The diameter of the circle of confusion defines what level of blur is considered out of focus, but in truth there is no correct
value since sharpness depends on how the image will be viewed and even then it is somewhat subjective.
You can think of the circle of confusion like this. Suppose you photograph a very bright but tiny spot of light such as a star
in the night sky. In a perfect world, all the starlight entering the lens would focus at a single point. In practice, the image is
spread out to some degree and can be approximated as a circular disk. The diameter of that disk is the circle of
confusion.
For a digital camera, if the circle of confusion is the same size as or smaller than a single pixel on the sensor, the image
will be more of less perfectly sharp. In practice, this is unrealistic since many factors conspire to prevent perfectly sharp
images, including lens misalignment and distortion, antialiasing filters, sensor dithering patterns, camera vibration during
the exposure, and so on. For this reason, reducing the diameter of the circle of confusion below roughly 2 pixel widths
usually does not make the image any sharper.
The smaller the circle of confusion you require, the sharper the image, but the narrower the depth of field and the more
you need to worry about diffraction. The circle of confusion can be calculated in various ways, each of which has its own
rationale.
DoF provides three methods for deciding what circle of confusion to use.

Sharp Image: captured images are about as sharp as the camera can produce.
In most cases, this is the most conservative method as it yields the sharpest images with the narrowest depth of
field. The circle of confusion computed this way can be significantly smaller than for the Sharp Print method (see
below). For film cameras, film resolution substitutes for digital sensor resolution, but otherwise the considerations are
similar – using this method makes as sharp a film positive or negative as possible consistent with the film's
resolution.

Sharp Print: a print of a standard size looks sharp to a viewer with standard vision from a standard distance.
This is the method generally used by camera manufacturers to mark lens barrels. By somewhat arbitrary convention
they assume a 12" print viewed from around 18". Since larger prints are normally viewed from a greater distance, this
works fairly well over a range of print sizes. Note that this method does not work very well if you crop the image
significantly before printing it or if you examine your prints from a closer distance.

Custom CoC: you enter a custom value for the circle of confusion.
To add a new camera, remove an existing camera or edit camera settings, click
Properties… from the drop-down menu. This displays the Camera dialog box.
and select Edit Camera
The information you supply in this dialog is used to calculate an appropriate circle of confusion value for any camera you
want to use.
Inputs:
Name
Enter a name for the camera settings. You can create multiple settings for the same camera if
you want to use alternate methods for computing the circle of confusion – just assign each one a
different name so you can tell which is which.
Method
Select Sharp Image, Sharp Print, or Custom CoC, depending on the method you want to use to
calculate the circle of confusion.
Type
Select Digital or Film depending on the type of camera.
Focal Length
Select Enter actual or Enter 35mm equivalent.
Most camera lenses are marked with their actual focal length in millimeters and you should use
Enter actual in this case. However, a few cameras are marked with 35mm equivalent focal
length (computed by multiplying the actual focal length by the crop factor). If you select Enter
35mm equivalent, DoF will divide the focal length you enter via the focal length scale by the
camera crop factor to determine the actual focal length to use to compute depth of field. This
option is provided as a convenience so you will not have to divide by the crop factor yourself.
Note that the metadata stored in JPEG or raw files always records the actual focal length and
not the 35mm equivalent.
Frame width (mm)
Frame height (mm)
Enter the sensor width and height in mm. For example for a full frame 36x24mm sensor, enter
36.0 for the width and 24.0 for the height.
Some common frame sizes are listed below:
Name
Dimensions
1/2.5"
1/2.3"
1/2"
1/1.7"
1/1.6"
1"
4/3"
APS C
APS C
35mm
6x4.5
6x7
4x5
5x7
8x10
5.76x4.29
6.16x4.62
6.4x4.8
7.6x5.7
8x6
13.2x8.8
17.3x13
22.5x14.8
23.6x15.7
36x24
60x45
70x60
127x102
178x127
254x203
Comments
Crop Factor
Nikon/Sony
Four Thirds and Micro Four Thirds
Canon
Nikon and others
Full frame 35mm
Medium format
Medium format
Large format
Large format
Large format
6.25X
5.84X
5.63X
4.74X
4.5X
2.7X
2.0X
1.6X
1.5X
1.0X
0.6X
0.52X
0.28X
0.20X
0.14X
For your camera's exact sensor dimensions, consult www.dpreview.com (locate the camera
review and look at the Specifications page) or your camera manual.
Frame width (pixels) Enter the sensor width and height in pixels. For example if your camera has a 6000x4000
Frame height (pixels) pixel sensor, enter 6000 for the width and 4000 for the height. For the exact dimensions of your
camera's sensor in pixels, consult www.dpreview.com (locate the camera review and look at the
Specifications page) or your camera manual. Or just check the width and height of the image
files in pixels.
Film resolution
Film resolution in line pairs/mm. (for film cameras only)
Typical values for high contrast targets vary from around 100 (Ektachrome) to 150
(Provia/Velvia) to 200 (Ektar 25). Values for low contrast targets are typically about half the high
contrast values. Appendix A lists resolutions of a number of different print and slide film types.
Using an average of the high and low contrast resolution numbers gives a typical value.
Custom CoC
Custom circle of confusion in mm.
If you are using the Custom CoC method, this is where you enter the circle of confusion you
want to use.
Allowable blur
Enter the maximum allowable blur in pixels or visually resolvable details. The standard value is
about 2.0 or possibly as low as 1.5 to be very conservative. Using 1.0 is overkill since Bayer
dithering and anti-aliasing filters make resolution at the pixel level impractical, and few if any
lenses are sharp enough to actually resolve usable detail down to the size of an individual pixel.
This parameter is a more or less arbitrary scale factor so it can be used to tweak the calculated
circle of confusion size to suit personal preference.
Visual Resolution
Enter the smallest angle in arc minutes resolvable by the observer. The value for this setting is
approximately 1.0 for observers with normal eyesight. Smaller values reduce the size of the
circle of confusion proportionally when using the Sharp Print method.
Print size
Enter the larger dimension in any convenient units. For example for an 8x12 print, enter 12.0.
Viewing distance
Enter the viewing distance in the same units as the print size. Larger prints are usually viewed
from a greater distance.
Wavelength
Enter the wavelength of light in nanometers (nm) to use to compute diffraction effects. The
default value of 550 nm is commonly used as it is roughly in the middle of the range of visible
wavelengths. For ultraviolet or infrared photography, you may want to select values more
appropriate for the wavelengths of light illuminating the subject.
The following outputs are computed and displayed when you click the Apply button
Circle of Confusion
The calculated diameter of the circle of confusion in mm. This number is computed based on the
other settings.
Diffraction Limit
The f stop at which diffraction blur is equal to the circle of confusion. At f stops greater than this
value, diffraction is the limiting factor in getting the sharpest possible image.
Crop Factor
The ratio of the width of a standard 35mm film frame to the camera's frame width. This is the
factor by which images need to be enlarged to match those from a full frame sensor camera.
Megapixels
For digital cameras, this is the total number of pixels per frame in millions. For film cameras, this
is the equivalent number of megapixels based on the film resolution in line pairs per millimeter,
computed at two pixels per line pair.
Buttons:
Apply
If you change any of the settings, you can click Apply to refresh the displayed Circle of
Confusion, Diffraction Limit and Crop Factor.
Prev
Clicking this button advances to the previous camera (if any).
Next
Clicking this button advances to the next camera (if any).
New
Clicking this button appends a new camera to the end of the list. Fill in the camera name and
other data before continuing. As a convenience, the initial values for all the settings except the
camera name are copied from the current camera. The camera list is automatically sorted
alphabetically when you close the Camera dialog.
Delete
Clicking this button deletes the current camera. You cannot delete the last camera since there
must always be at least one set of camera settings available.
When you are done making changes, simply exit the dialog box to return to DoF.
Practical Considerations
What circle of confusion should I use?
Sharp Print
Use this method if your primarily interest is creating prints that will be viewed from a normal distance. If you plan to
make large prints or prints that will be viewed from close up, adjust the camera settings accordingly so the circle of
confusion will be reduced.
Sharp Image
Use this method if you want your images to be tack sharp, right down to the pixel level. If the resulting depth of field is
too narrow to be useful, you can always allow blur values greater then 1.0 and deliberately trade off some image
sharpness for increased depth of field, or you can try focus stacking.
What mode should I use?
Depth of Field and Best f Stop Modes
Use Depth of Field mode when you know the focal length, f stop and focus distance you are going to use and you
want to determine the range of distances that will be in focus. This is often the least useful mode because the
desired depth of field is usually determined by the scene you are trying to photograph. In this case use Best f Stop
mode which lets you work backwards from the required depth of field to determine the best f stop and focus distance
for a given lens.
Focus Stacking Mode
Use this mode when you can't get enough depth of field with a single image and you plan to use focus stacking
software to merge multiple images shot with different focus distances. After a while, you will develop a feel for the
required intermediate focus points since they require turning the focus ring by equal angle increments between the
near and far focus limits.
Blur Mode
Use this mode when you want to determine how much blurring will occur at a given distance in front of or behind the
focus plane. For example, if you want to compare two lenses for taking portraits to see which one blurs the
background more. Or to determine what focal length and f stop combination to use to blur the background or
foreground by a specific amount.
Macro Mode
Use this mode for macro photography, where camera-to-subject distances are short and magnifications are high.
First photograph a ruler oriented horizontally across the entire width of the frame. Next, read off the width of the field
of view from the image and enter it into DoF. Depth of field can then be computed from the magnification which in
turn is computed from the frame width. In Macro mode, you do not need to enter the lens focal since the depth of
field depends only on magnification.
What is the best distance to focus at?
The near focus limit, the far focus limit and the focus distance are related such that the values of any two determine the
third. You can do this graphically by setting DoF to Best f Stop mode.
Case 1: given near and far focus limit, determine the focus distance
Drag the lower red line to the near focus limit and the upper red line to the far focus limit. The focus distance is
indicated by the location of the green line.
Case 2: given the near focus limit and the focus distance, determine the far focus limit
Drag the lower red line to the near focus limit and drag the upper red line until the green line is located at the focus
distance. The location of the upper red line now indicates the far focus limit.
Case 3: given the far focus limit and the focus distance, determine the near focus limit
Drag the upper red line to the far focus limit and drag the lower red line until the green line is located at the focus
distance. The location of the lower red line now indicates the near focus limit.
What lens and f stop should I use?
Set DoF to Best f Stop mode and select your camera and lens focal length. Then position the two red lines according to
the desired near and far focus limits.
DoF displays the f stop that yields the smallest combined diffraction and focus blur. The Blur scale shows you how much
blurring occurs at the near and far focus limits. If the blur is unacceptable you may need to narrow the range between the
near and far limits or use focus stacking. To explore focus stacking, switch to Focus Stacking mode and increase of
decrease the number of images until the blur value becomes acceptable.
How blurry will be background be?
Set DoF to Blur mode and select your camera, lens focal length and f stop. Position the green line to the distance at
which the lens is focused and the red line to the distance to the object whose blur you want to determine. DoF displays
the amount of blur on the blur scale.
How do I use DoF for macro focus stacking?
Suppose you are using an automated macro slide that uses a stepper motor to advance the camera between shots, and
you need to determine the required step size so the composite image will be uniformly sharp. First measure the field of
view by photographing a ruler at the subject distance. Then, set DoF to Macro mode and select your camera, field of
view, f stop and allowable blur. The required step size must be less than or equal to the total depth of field. If the step
size comes out too small, you can try using a smaller aperture or increasing the allowable blur, but be aware that you will
be giving up some sharpness to diffraction, focus blur or both.
How do I compare multiple scenarios? (Windows version only)
You can launch multiple copies of DoF in different windows, and this can be useful for comparing the results from
different sets of inputs. If you do this however, you need to be aware that the settings from the last window you close will
overwrite those from any previous windows.
Synchronizing Camera Data and Settings (Windows version only)
All settings are saved in a file called dof.txt when you exit DoF and restored when you start it up again. When dof.txt is
saved, a backup copy of the previous settings file, if any, is saved in a file called dof backup.txt.
If you have a Dropbox folder on your computer, settings are saved in a subfolder of the Dropbox folder named apps\DoF.
This means that any changes such as adding a new camera or tweaking the advanced settings are automatically
synchronized across multiple computers. If no Dropbox folder is present, settings are saved in C:\ProgramData\DoF and
you must synchronize settings between computers manually.
Please do not edit dof.txt directly using a text editor as any error you accidentally introduce could cause DoF to
become unstable or you may lose all your camera settings. Always make changes via the Camera dialog if
possible. If dof.txt becomes corrupted, you can try using dof backup.txt to recover. If all else fails, delete the
setttings file and DoF will use default settings the next time it runs.
Appendix A – Film Resolution
The best modern general purpose films resolve as many as 200 lines/mm when photographing high contrast test targets
under ideal conditions, although for normal subjects of reduced contrast resolution is considerably lower. The following
table lists the resolution of some commercially available films. The two numbers for the resolving power are for high
contrast and low contrast test targets.
Print Films
Royal Gold 25/Ektar 25
Agfacolor Ultra 50
Konica Impresa 50
Agfacolor HDC 100
Agfacolor HDC 100 Plus
Fujicolor Superia Reala 100
Fujicolor Superia 100
Fujicolor Super G Plus 100
Kodacolor Gold Plus 100
Konica Color Centuria 100
Agfacolor Optima 125
Kodak Royal Gold 100/Ektar 125
Agfacolor Portrait XPS 160
Fujicolor NPS 160 Professional
Vericolor III 160
Konica SR-G 160
Agfacolor Optima 200
Agfacolor HDC 200
Agfacolor HDC 200 Plus
Fujicolor Superia 200
Fujicolor Super G Plus 200
Kodacolor Gold Super 200
Konica Color Centuria 200
Agfacolor Optima 400
Agfacolor HDC 400
Agfacolor HDC 400 Plus
Fujicolor Super G Plus 400
Fujicolor 400 Pro NPH
Fujicolor NPH 400
Fujicolor Superia 400
Konica Color Centuria 400
Kodak Gold 400
Fujicolor Super NHG II Pro 800
Fujicolor Superia X-Tra (800)
Konica Color Centuria 800
Kodak Royal Gold 1000/Ektar 1000
Kodacolor Gold 1600
Fujicolor Superia (1600)
lp/mm
200/80
140/50
130/80
130/50
130/50
125/63
125/63
130/50
100/50
125/63
140/50
160/NA
150/60
125/63
100/40
100/50
130/45
130/50
130/50
125/55
100/50
100/50
100/50
100/50
100/50
130/50
100/50
100/50
100/50
125/50
100/50
100/NA
100/50
100/50
100/50
80/NA
80/NA
90/45
General Purpose Slide Films
Kodachrome 25
Agfachrome RSX 50
Fujichrome Velvia 50
Ektachrome 64
Kodachrome 64
Agfachrome CT Precisia 100
Agfachrome RSX II Pro 100
Fujichrome MS 100/1000
Fujichrome Astia 100
Fujichrome Provia 100
Fujichrome Provia 100F
Fujichrome Sensia II 100
Imation Chrome 100
Ektachrome 100
Konica Chrome R-100
Agfachrome RSX II Pro 200
Agfachrome CT Precisia 200
Fujichrome Sensia II 200
Ektachrome 200
Kodachrome 200
Fujichrome Provia 400
Fujichrome Provia 400F
Fujichrome Sensia II 400
Imation Chrome 400
Fujichrome Provia 1600
Ektachrome P1600 Pro
Tungsten Balanced Slide Films
Kodachrome 40
Fujichrome 64 T
Ektrachrome 64T
Ektachrome 160T
Black and White Films
Agfapan APX 25
Technical Pan 2415
Agfapan APX 100
Fortepan 100
T-MAX 100
Plus-X 125
Fortepan 200
Agfapan APX 400
Fortepan 400
Tri-X 400
T-MAX 400
T-MAX P3200
Special Purpose Films
High Speed Infrared
Ektachrome Slide Dup
Ektachrome SO-366
Agfa Scala 200X
Polaroid Polachrome/HC
Polaroid Polapan
lp/mm
100/63
125/55
160/80
125/50
100/63
130/50
125/50
135/55
135/55
140/60
140/60
135/55
94/NA
100/50
125/50
110/50
120/50
125/50
125/50
100/50
125/40
135/55
125/40
89/NA
100/40
80-63/NA
100/63
135/55
125/50
125/50
200/NA
320/100
150/NA
90/NA
200/63
125/50
85/NA
110/NA
80/NA
100/50
125/50
125/40
80/32
125/63
125/63
120/50
90/NA
90/NA
Some film manufacturers rate film resolution by publishing an MTF curve instead of listing lines per mm. You can infer
the resolution in lines per mm for high contrast subjects by looking at where the MTF curve drops to about 20%.
Appendix B - Real World Examples
The following examples are based on the Sharp Image method of computing circle of confusion and looking at the
effects on fine image detail. An example based on the Sharp Print method would require printing the images and looking
at them from the right distance, and this does not lend itself to presentation in an electronic document.
Appendix B1 - Depth of Field Blurring Example
To illustrate blurring caused by a subject being offset from the focus distance, I photographed a resolution test target
using an Olympus OM-D EM-1 mounted on a copy stand. I attached a 45mm macro lens, set the aperture to f/4 to
minimize diffraction, adjusted the distance from the camera to the target to 30”, and carefully focused the camera on the
target. Then I took a series of photos, lowering the camera 1/8” at a time while leaving the camera focused at 30”.
According to DoF, the image should remain sharp up to 0.316” closer than the 30” focus distance. This predicts the
images at 0.000”, 0.125”, 0.250”, and 0.375” front focus should all be sharp, with the last one perhaps being a little soft.
Beyond this point the images should get progressively softer.
I shot raw files leaving the images completely unsharpened. As long as sharpening is applied consistently to all the
images it shouldn’t make any difference to side-by-side comparisons, but I wanted to get the most accurate possible view
of the sensor data. Normal image workflow would naturally produce slightly sharper images. I cropped the images down
to just the central area (roughly 170x150 pixels) of each image as shown in red below:
Finally I assembled the cropped images taken at different distances from the target and created the following composite:
As predicted, the first four images have about the same sharpness and the image gets steadily softer as the subject
distance continues to get smaller. The red numbers indicate how far in inches the camera was moved closer to the
target.
Appendix B2 - Diffraction Blurring Example
To illustrate blurring caused by diffraction, I photographed the same resolution test target using the same camera and
lens as in the previous example. In this case I varied the f stop from f/2.8 to f/22 (compensating by increasing the
exposure time accordingly), holding the target distance fixed at 30” with the camera focused accurately on the target. As
the f stop increases, so does diffraction blur. According to DoF, the values of diffraction blur are roughly:
f/2.8
f/4
f/5.6
f/8
f/11
f/16
f/22
0.47
0.67
0.93
1.33
1.83
2.56
3.66
Since diffraction blur only becomes visible at around 1.00 (i.e. when it is comparable to the circle of confusion), at f/2.8
and f/4 images should be sharp, at f/5.6 very slightly blurry, and the rest progressively softer.
The actual images (again from unsharpened RAW files) look like this:
Appendix B3 - What Different Amounts of Blurring Look Like
DoF displays a measure of how much images are blurred as compared to the circle of confusion, so values of 1.0 or
lower should be acceptably sharp. To give you an idea of what images with larger amounts of blur look like, I did the
following experiment.
First I set up an Olympus OM-D EM-1 with a 75mm lens (which is one of the sharpest available lens for this system),
aperture f/4, 20 feet away from a test target taped to the wall. I had already calculated how much blur DoF predicts the
image will exhibit for a subject at 20 feet,if the camera is focused at various distances less than 20 feet. I then focused
on a series of targets at distances corresponding to various amounts of blur and then using that focus setting took
photographs of the target 20 feet away. This produces a series of images of the same subject at the same size blurred
by known amounts.
First, here is the overall scene:
As before, I processed raw files with no sharpening and cropped the images down to a central region containing just the
target. The first image was focused exactly on the target and is thus about as sharp as the camera and lens can deliver.
Due to diffraction, the predicted blur is 0.67. Subsequent images were focused at closer distances calculated so as to
produce increasing amounts of blur as indicated by the red number in the upper left corner of each one:
Appendix C - Depth of Field Equations
Definitions
L = focal length in mm.
A = focus at distance in mm.
f = f stop (aperture/focal length)
Dn = near focus distance in mm.
Df = far focus distance in mm.
H = hyperfocal distance in mm.
D = subject distance in mm.
Bd = diffraction blur in mm.
Bf = focus blur in mm.
c = diameter of CoC in mm.
m = magnification factor
Diffraction Blur in mm given f (for green light)
Bd = f/750
Focus Blur in mm given f, L, A, D
Bf = ∞
Bf = 0
2
Bf = L /(f*D)
2
Bf = L /(f*(A – L))
2
Bf = |(L *(A – D))/(f*D*(A – L))|
if A ≤ L
if A = D
if A = ∞
if D = ∞
f stop at which diffraction blur = circle of confusion
f = 750*c
A, Dn, Df given any 2 out of 3
Dn < Df , if Df = ∞, A = 2*Dn
A < 2*Df , if Df = ∞, Dn = A/2
A > Dn and A < 2*Dn, if Dn ≤ A/2, Df = ∞
A = 2*Dn*Df/(Dn + Df)
Dn = A*Df/(2*Df – A)
Df = A*Dn/(2*Dn – A)
Hyperfocal distance, near and far focus limits
2
H = L /(f*c) + L
2
2
Dn= (A*(H – L))/(H + A – 2*L) = A*L /(L + f*c*(A – L))
2
2
Df = (A*(H – L))/(H – A) = A*L /(L – f*c*(A – L))
f stop for best tradeoff between diffraction and focus
f = L*sqrt((750*(A – Dn))/(Dn*(A – L)))
A > L and A > Dn
Distance range at which a given focus blur occurs
2
if A = ∞
if A = ∞
Dn = L /(f*Bf)
Df = ∞
2
2
Dn = A*L /(L + f*Bf*(A – L))
2
2
Df = A*L /(L – f*Bf*(A – L))
A>L
A > L if Df < 0, Bf not reached even at ∞
Macro total depth of field for a given magnification
DOF = 2*f*c*(m + 1)/m
2
m>0
Harmonic and inverse harmonic scale given lower and upper limits
x = harmonic scale [0..1]
y = linear distance [A..B]
y = A/(1 – (1 – A/B)*x)
x = (1 – A/y)/(1 – A/B)
if B = ∞, y = A/(1 – x)
if B = ∞, x = 1 – A/y
Acknowledgements and References
Harold M. Merklinger, The Ins and Outs of Focus, available for download at:
http://www.trenholm.org/hmmerk/download.html
Norman Koren, Depth of Field and Diffraction:
http://www.normankoren.com/Tutorials/MTF6.html
Useful information can also be found in the Wikipedia articles on Depth of Field and Circle of Confusion.
Copyright  1995-2015, Digital Light & Color
All Rights Reserved
Written by Jonathan M. Sachs
jsachs@dl-c.com
http://www.dl-c.com
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