note 1: Calculations based on adequate focus for an 8x10 inch print. (Long considered the standard for depth of field) note 2: For digital cameras, enter actual lens focal lengths, not 35mm equivalent focal lengths.
(1 foot = 0.3048 meters)
Knowing what will appear to be in focus (and what will be out of focus) is one of the most basic considerations when making any photograph. Although exact focus occurs only at the precise focusing distance, depending on film format, lens focal length, aperture size and focus distance, the apparent range of focus, or depth of field, can vary considerably. Additionally the size of a print made from the film will have an effect on this apparent depth of field. It should be noted that an 8x10 inch print has long been considered the standard by which most lens manufacturers base their depth of field guidemarks on.
Without going into the physics involved, this apparent depth of field is due to an optical phenomena called circle of least confusion. When an object is at the exact distance the lens is focused, every point on the object will focus to a point on the film plane. When an object moves out of focus, on the film these points begin to grow and become circles. The farther out of focus an object is, the larger these circles become. But up to a certain point (again depending on film or electronic sensor size, lens focal length, etc.), these circles of confusion are unobtrusive (unresolved by the human eye) and the image appears to be in focus over a range of distances and has 'depth of field'.
The same factors that affect depth of field in film cameras apply to digital cameras too: aperture f-stop, focus distance, lens focal length, film format (essentially the size of the 'light recording area' whether a piece of film or an electronic sensor), and of course, the final print size (traditionally, 8x10 inch).
But unlike film cameras which use a handful of standardized film sizes (35mm, 6x7, 4x5, etc.), digital cameras are being made with numerous different sized image sensors. This makes determining the all important Diameter of the Circle of Least Confusion parameter used in the calculations a laborious and ongoing task for each and every digital camera model! Fortunately, there's an easy "shortcut" that yields accurate results.
By dividing the Equivalent 35mm Focal Length by the camera's Actual Focal Length we derive a number, The Lens Multiplier Factor, that can be used to interpolate an acceptable Diameter of the Circle of Least Confusion for use in depth of field calculations for our digital camera.
For digital camera bodies that use interchangeable lenses the manufacturer usually specs this Lens Multiplier Factor. (A Pentax K10D, for example, has a Lens Multiplier of 1.5, while Canon specs the EOS D1 as having a Lens Multiplier of 1.3.)
Do the Math:
Important Note about Diagonal Length of Sensor: In investigating this approach, I discovered that the size many manufacturers spec for image sensors is not necessarily the portion of sensor area that is actually used to record the image. This makes this method highly suspect! If you determine the LMF for your camera this way, be aware that it most likely will be a very conservative number, meaning the usable depth of field available may be greater than the calculators indicate.
Note 1: Based on acceptable sharpness for an 8x10 inch print. Note 2: Multiply Inches by 25.4 to convert to Millimeters. Divide Millimeters by 25.4 to convert to Inches.
Hyperfocal Distance Setting focus at the Hyperfocal Distance gives maximum depth of field from H/2 to infinity.
Near Focus Limit
Where: NF = Near Focus Limit (millimeters) H = Hyperfocal Distance (in millimeters, from above equation.) D = lens focus distance (in millimeters) L = lens focal length (ie, 35mm, 105mm)
Far Focus Limit
Where: FF = Far Focus Limit (millimeters) H = Hyperfocal Distance (in millimeters, from above equation) D = lens focus distance (in millimeters) L = lens focal length (ie, 35mm, 105mm)
order
