ExpoImaging ExpoAperture - Manual (Page 22)

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3b. Using a Focal Length Greater Than 300mm
In order to find the aperture setting for a desired distance
range using a lens with a focal length larger than 300mm,
divide the focal length by 5 and the distance range by 25,
and then proceed using the new numbers in the “standard”
manner. See the following example.
NOTE: If the procedure above results in a partial depth-of-field
zone, and is not automatically given on your ExpoAperture
Depth-of-Field Guide, then you may need to refer to section 5a.
of these instructions: “Setting the aperture for a Distance Range
of Less than One Zone” to find the preferred aperture setting.