If you, like me, is in love with bobble bokeh’s then you’re looking for small depth of field, where you isolate your motive against an out-of-focus background, with highlights creating its magic. Its nothing new to most that the key is to use a small f-number, get close, and use a long focal length lens, but are you familiar with everything that drives a shallow depth of field ?
The rules of thumb
3 factores goes into controlling the Depth of Field (DOF), Aperture (f/number), Subject Distance and the Focal Length.
The Aperture range identifies the widest to smallest range of lens openings, i.e. f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22 and f/32. Each f-number is represents one “stop” of light, a stop calculated as the focal length of the lens divided by the diameter of the aperture opening. The bigger the lens opening the shallower is the depth of field. if the diameter of the Aperture is doubled, then is the Depth of field also doubled.
Subject Distance, the farther away an object is and focused on, the deeper is the DOF. If the subject distance is doubled, then the depth of field is increased by four times.
Focal Length, we already touched on that the focal length goes into the f/stop calculations. If the focal length is doubled, then the depth of field is decreased by four times, DOF is inversely proportional to the focal length squared.
Apps is makes life easy
There is several apps for your phone making the DOF calculations with ease. They allows photographers to calculate the depth of field and hyper focal distance for any given settings. What you get is a calculated near limit, far limit, total depth of field.
There is also online versions, like the DOF Master, personally I am not in favor of the online version, while it does me little good in the field.