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.
Four 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. 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. All four standards .03, .024, .02, and .01 apply to Full Frame cameras, for other formats the final CoC is the Blur Standard divided by the Crop Factor.
The program also allows you to enter the CoC directly. Values between .001 and .05 are available.
Focal length is the actual focal length of the lens, not the full frame equivalent.
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.
The hyperfocal distance is the shortest distance beyond which all objects can be brought in into acceptable 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. If you wish to include very distance objects in your image you should focus at twice the distance to the nearest object. If this distance is less than the hyperfocal distance then distant objects will not be in sharp focus and you should increase the aperture until they are. If the focus distance is greater than the hyperfocal distance then the overall image will be sharper than if you had focused at the hyperfocal point. 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.
The full frame equivalent focal length of a lens is the actual focal length times the crop factor.
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.
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.
When the far distance 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.
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.
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.
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.
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.
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.
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.
Enter the distance to the closest point in the scene and select the units of measure. Distances can be entered in feet, inches, meters, or centimeters. The same units are used for the near distance, far distance, and focus distance. Outputs will be in the chosen unit measure as well.