Using Depth of Field Calculators
With a typical depth of field calculator, you enter the aperture (f-stop) you are using the focal length of the lens, and the distance the lens if focused at, and the calculator will tell you the near and far depth of field limits, plus the hyperfocal distance for the f-stop and focal length combination you selected. If you don't have enough depth of field for the scene you want to photograph, change the f-stop, focused distance, or lens focal length until the calculator tells you you have enough DOF for your scene. Then take you lens and set you lens focal length, f-stop, and focused distance indicated on the calculator.
When using a depth of field calculator, the most critical data to enter is the Circle of Confusion (CoC) value that you want the calculator to use. The CoC value depends on the format of the camera you are using and the size of print you want to make. Enter the wrong CoC value for your camera format and the calculator won't give you the right results. If the DOF calculator doesn't allow you to input your own CoC values, I would suggest finding a different DOF calculator.
In my opinion, the default CoC values for some calculators won't allow an adequate amount of DOF. They are often calculated for a print no larger than 8x10 inches. If your DOF calculator allows you to select your brand and model of camera, you may not be happy with the results you get. It is preferable to enter your own CoC values.
These are the Circle of Confusion values I recommend for making prints up to 11x16 inches in size for the following camera formats:
CoC = 0.023mm for full frame digital SLRs (24x36mm sensor) and 35mm film cameras
CoC = 0.018mm for a 1.3x field-of-view-crop digital SLR
CoC = 0.014mm for a 1.6x or 1.5x field-of-view-crop digital SLR (15x23mm sensor)
CoC = 0.012mm for a 2x field-of-view-crop digital SLR
CoC = 0.004mm for a fixed lens, point-and-shoot digital cameras (4.31x6.75mm sensor)
Here's my favorite online DOF calculator. If you scroll down far enough on the drop down menu (past the long list of cameras), you can enter your own CoC value in mm. For example use this online calculator and use 0.023mm for the CoC value (the value for a for a full frame digital camera or 35mm film camera). Set the focal length to 50mm, the f-stop to f/8, and the focused distance at 10 feet, and click CALCULATE. The depth of field is from 8.26 feet to 12.7 feet. The hyperfocal distance is 46.8 feet (with the hyperfocal distance formula I use, the hyperfocal distance is 45.16 feet which is pretty close).
Keep in mind that DOF calculations are much more exact that DOF in real life. With medium to wind angle lenses, DOF changes gradually from very sharp to pretty sharp to sharp to slightly out of focus to more out of focus.
Let's take the above example. If the calculated near depth of field is 8.26 feet, that doesn't mean things are sharp at 8.27 feet and blurry at 8.24 feet. What it means is anything 8 feet from the camera will look pretty sharp, anything 6 feet a way will look a little softer, and anything 4 feet away will be softer yet. 10 feet will be very sharp, 12 feet pretty sharp, 14 feet a little softer, and 16 feet softer yet. So don't stress out over a few decimal points in a DOF chart or the results from a DOF calculator.
Now use the online calculator and set the focused distance to the hyperfocal distance of 47 feet (I am rounding off). The DOF is now 23.4 feet to infinity. Note that the near depth of field limit is half the hyperfocal distance.
Manual DOF Calculators
Manual DOF calculators look like circular slide rules. You can buy a commercial version like the ones at ExpoImaging (scroll down the page to the ExpoAperture 2 Depth of Field Guides), or you can make your own using Windows software by going to DOFMaster.
DOF Calculators for Smart Phones and PDAs
DOF Calculators are also available for smart phones and PDAs. Read more here.
Depth of Field Articles:
My new photography book, Digital Photography Exposure for Dummies, has two complete chapters (a total of 40 pages) devoted to an in depth look at depth of field.
December 13, 2010
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