DOF Easy Help
This program is unique among Depth of Field Calculators. With most DOF Calculators you enter the focus distance and the aperture and the calculator tells you whether your scene will render in focus. DOF Easy starts with information about the scene (a range of distances) and DOF Easy tells you where to focus and what aperture to use. It also shows blur amounts as a function of distance. Users can easily see how the amount of blur, in pixels, changes with distance from the focal plane.
DOF Easy is designed to be "easy". While all inputs are required, defaults are available for most of them. Key inputs are saved between runs so they do not have to be re-entered. Key outputs are shown first. These include optimal focus distance and aperture, and the amount of blur at the near and far points in your scene. Blur diameters are stated in simple to understand pixels as well as in millimeters. The hyperfocal distance is also shown. The program also computes a variety of additional outputs. These include information about the sensor, the lens, the diffraction limited aperture, and a detailed table showing how blur changes with distance.
If a field has a dotted underline then additional help on the input can be obtained by clicking or pressing on the underlined text.
Camera Format provides information about the size and aspect ratio of the sensor. DOF Easy saves this information when you exit the program. It reloads the Camera Format on next use. Camera Format is used to calculate the crop factor and the effective focal length of the lens. It is also used to determine the standard of blur, commonly known as the circle of confusion (CoC). If you do not know the Camera Format you can search for it at https://www.digicamdb.com.
The Blur Standard, together with the Camera Format, determines the acceptable Circle of Confusion (CoC). The CoC is an optical spot caused by light rays not coming to perfect focus when a point source is imaged. When the CoC is small an image is perceived as sharp. What is perceived is sharp depends on the observer's vision, whether the image is viewed as a print, on screen, or via a projector, and on the viewing distance.
Four different general standards are available in the program: Normal, Fine, Professional, and Ultimate. The "Normal" standard is the historical criterion of .03 mm. This standard is good for prints of up to 8 inches by 10 inches when viewed at ten inches by a person of normal vision. It is also good for web use. A "Fine" standard of .024 mm that is 20% sharper is also available, as are a "Professional" standard of .02 mm or 50 lines/mm, and an "Ultimate" standard of .01 mm or 100 lines/mm which is close to the resolution of modern day sensors. The last two standards should only be used with the very sharpest of lenses. All four standards .03, .024, .02, and .01 apply to Full Frame cameras. For other formats the effective CoC is the Blur Standard divided by the Crop Factor. For example if "Professional" is chosen as the blur standard and "Canon APS-C" the Camera Format the final CoC is .02 / 1.6 = .0125.
The program also allows you to enter the acceptable CoC directly. Values between .001 and .05 are available. No Crop Factor adjustment is made to the CoC in this case.
The program also saves the "Blur Standard" choice between runs so it only needs to be entered once.
Focal length is the actual focal length of the lens, not the full frame equivalent.
Aperture strongly affects depth of field. Except for macro work the hyperfocal distance is inversely proportional to the aperture, so doubling the aperture, say from f/8 to f/16 will decrease the hyperfocal distance by a factor of 2.
When selecting an aperture keep both lens quality and diffraction in mind. Lenses are usually their sharpest one or two stops slower than wide open. For example, an f/2.8 lens would be sharpest when shot at f/4 or f/5.6. Due to the effects of diffraction lenses start losing resolution at about f/11. Resolution at f/16 is typically about 20% less than resolution at f/8, and resolution at f/22 is about 50% less than f/8.
Near Distance is the distance to the closest point in the scene. Also enter the units of measure. Distances can be entered in feet, inches, meters, or centimeters.
Far Distance is the distance to the furthest point in the scene.
Focus Distance is the distance at which the lens is focused. It is filled in automatically when you enter the near and far distances into the program and click or press on the small green calculator icon. The calculator icon computes the harmonic mean of the near and far distances, which is mathematically the optimal focus distance.
The focus distance can also be entered directly in the event that you do not wish to focus at the optimal point. This could be the case if you wish the background to be blurred, or if you wish the foreground or background to be a little sharper than the rest of the image.
Optimal focus distance is the distance at which you should focus in the absence of unique conditions. It depends only on the distances to the closest and furthest points in the scene and is independent of focal length and aperture. It is the harmonic mean of the near and far distances. If nd is the closest point in your image, and fd the furthest, the harmonic mean is given by
harmonic mean = 1/(average(1/nd,1/fd))
When the far distance fd is infinity the harmonic mean is just twice the near distance. For all distances the harmonic mean is less than the average of the near and far distances, i.e. you should always focus closer to the nearest point than the average.
Required Aperture is the smallest f-stop at which objects at the near and far distances will be in sharp focus. Sharp focus is defined as blur less than or equal to the acceptable CoC. The required f-stop is calculated assuming you have focused at the Optimal Focus Distance.
Nearest Sharp Point is the distance to the closest point in the scene that will be in sharp focus. Sharp focus is defined as blur less than or equal to the acceptable CoC.
Furthest sharp point is the distance to the furthest point in the scene that will be in sharp focus. Sharp focus is defined as blur less than or equal to the acceptable CoC.
Total depth of field is the difference between the far and near points of acceptable focus. It depends on where you are focused, the CoC, and the aperture.
Blur at Near Distance (mm) shows the amount of blur on the sensor of the closest point in the scene. It is defined as the diameter of the blur circle on the sensor in mm. The Blur at Near Distance is color coded. When the amount of blur is less than or equal to the acceptable CoC the Blur at Near Distance is shown in green, with darker colors indicating less blur.
Blur at Far Distance (mm) shows the amount of blur on the sensor of the furthest point in the scene. It is defined as the diameter of the blur circle on the sensor in mm. The Blur at Far Distance is color coded. When the amount of blur is less than or equal to the acceptable CoC the Blur at Far Distance is shown in green, with darker colors indicating less blur.
Blur at Near Distance (pixels) shows the amount of blur on the sensor of the closest point in the scene. It is defined as the diameter of the blur circle on the sensor in pixels. The Blur at Near Distance is color coded. When the amount of blur is less than or equal to the acceptable CoC the Blur at Near Distance is shown in green, with darker colors indicating less blur.
Blur at Far Distance (pixels) shows the amount of blur on the sensor of the furthest point in the scene. It is defined as the diameter of the blur circle on the sensor in pixels. The Blur at Far Distance is color coded. When the amount of blur is less than or equal to the acceptable CoC the Blur at Far Distance is shown in green, with darker colors indicating less blur.
The Hyperfocal Distance (HF) is the shortest distance beyond which all objects can be brought in into acceptable focus. It depends on the aperture of the lens and the CoC. Note than when you are focused at the hyperfocal point all objects between the hyperfocal distance divided by two and infinity will be in sharp focus.
Note that the hyperfocal distance is not the distance at which you should focus your camera! Focusing at the hyperfocal distance is a mistake many photographers make. Before smartphones became readily available landscape photographers would carry "Hyperfocal Charts" with them on shoots. The charts showed, for a variety of apertures and focal lengths, the hyperfocal distance. If the scene includes very distant points you could quickly determine the aperture to use and get a good idea of where to focus since all point between the hyperfocal divided by 2 and infinity will be in sharp focus.
If the nearest point in the scene is further than the hyperfocal distance then focusing at the HF is not optimal. You will get a sharper image if you focus further out. Focus at twice the distance to the closest object in the scene.
The Acceptable Circle of Confusion (mm) (CoC) is the amount of blur in mm that is acceptable in the final image. It is computed from the Camera Format and the Blur Standard.
The Acceptable Circle of Confusion (pixels) is the amount of blur in pixels that is acceptable in the final image. It is computed from the Camera Format and the Blur Standard.
Fields here are shown for information only.
The diagonal, width, and height fields show the size of the sensor in millimeters.
The Pixels/mm field shows the number of pixels per millimeter of the sensor. This field is used to convert blur amount in mm to blur amounts in pixels.
mm/Pixel shows the size of a pixel on the sensor.
Lines/mm is Pixels/mm divided by two since one line consists of both a light pixel and a dark pixel.
Area/mm2 show the area covered by the sensor.
The Crop Factor is the ratio of the diagonal of a full frame camera (43.3 mm) to the sensors diagonal. Typical crop factors are 1.6 for a Canon APS-C camera, 1.5 for a Nikon DX camera and 2.0 for a Micro 4/3 camera by Olympus or Panasonic.
Fields here are shown for information only.
The Full Frame Equivalent Focal Length of a lens is the actual focal length times the crop factor. The FFE focal length is used to calculate the horizontal and vertical angles of view.
Horizontal field of view is the width in feet or meters of the observable world seen at the focus distance. It can be calculated as
Horizontal FOV = focus distance × (36/FFE focal length).
Vertical field of view is the height in feet or meters of the observable world seen at the focus distance.
Horizontal angle of view is expressed in degrees. It depends only on the full frame equivalent focal length and the aspect ratio of the camera.
Vertical angle of view is expressed in degrees.
The Airy Disk Diameter (mm) is the size of the blur spot caused by diffraction. It is a function of lens aperture. Stopped down lenses produce larger airy disks (blur). It is also a function of color temperature with reds showing the largest airy disks and blues the smallest. Blur Calculator uses 5250K as the default color temperature. 5250K is the color temperature of typical daylight. Airy disk size increases linearly with aperture, so an image stopped down to f/22 would have an airy disk nearly three times (22/8) larger than one at f/8.
Airy Disk Diameter (pixels) is Airy Disk Diameter (mm) × Pixels/mm. As sensor pixel density increases the size of the airy disk in pixels also increases.
Diffraction Limited Aperture is the aperture at which the airy disk exceeds one line pair (2 pixels) in size.
This section shows the amount of blur at various distances. Amounts of blur on the sensor are shown in both pixels and millimeters. Rows are highlighted in green when the amount of blur is less than the acceptable CoC. Darker greens indicate less blur.
For more detailed information about depth of field, achieving optimal focus, and creating high quality images please visit https://www.thewave.info/DOF/DOF.html
DOF Easy 1.0.0
Copyright (C) 2017 William H. Belvin
Designed and Programmed by William H. Belvin
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.