Depth of Field Simplified

I’ve noticed that a lot of searches regarding depth of field (and how to use your aperture to create a blurred or blurry background in your photos, or what is called bokeh) have led to my blog.  I’ve also received some good follow up questions from my previous post about depth of field.  Unfortunately, my post on Mastering Depth of Field may be a bit advanced for those who are still learning about how to use their digital SLR, as it is intended for more experienced photographers.

As I explained in that post:

“depth of field is…the range of distances in which the objects in the photograph will be acceptably sharp. For example, if I am using a 100mm lens, set my aperture at f/5.6, and focus on a subject 10 feet away, everything from 9.69′ to 10.3′ away from me will be acceptably sharp or in focus in the resulting image.”


Open Windows, San Miguel Duenas, Guatemala

Depth of field, then, can mean that everything is in focus from a few feet away to infinity (deep depth of field), or it can mean that a person’s eyes and nose are in focus, but their ears and hair and everything behind (and in front) of them is blurry (shallow depth of field).  One of the best ways to make use of depth of field is to create dramatic, shallow depth of field – the subject is in focus, but the background is blurry.  This technique helps to call attention to your intended subject and minimize distracting background elements, and to make your photos look much, much more like those of the pros.

All of the numbers and fractions and settings and seemingly reverse logic are intimidating at first, and most books add to the complication and confusion.  But it is really quite simple.  Depth of field is controlled by the aperture.  A small aperture size (which is an aperture number like f/16 or f/22) will create deep depth of field, with everything in focus.  A large aperture size (which is an aperture number like f/2.8 or f/4) will create a shallow, dramatic depth of field.  (Since “f/number” is a fraction, f/16 is a smaller number and size than f/4, so I’m avoiding using small number vs. large number terminology, as I said I would try to keep this from becoming too confusing…)   So here is the quick and simple way to create dramatic depth of field:


Open Windows, San Miguel Duenas, Guatemala

Set your camera on Aperture Priority Mode.  On a Canon, rotate the mode dial to Av, on Nikon set the dial to A.

Set your camera to Auto ISO.  Or else if you wish to control the ISO, if you are indoors or in dim light without a flash, set it to 800 or 1600 ISO.  If you are outside in bright sun, set it to 100 or 200 ISO.  If it is a bit cloudy or you are in the shade set it to 200 or 400 ISO.

Look in you manual for how to change the aperture setting of the lens.  For a Canon dSLR in Av mode, that means rotate the little finger dial up there by the shutter button.  On a Nikon it means rotate one of the dials at the top right front or back of the camera, depending on your camera and settings.)  Turn the dial until you see f/2.8 or f/4 or f/5.6 on your screen or in the viewfinder. Since you are in Aperture Priority Mode, the camera automatically selects an appropriate shutter speed.  If you’ve selected the ISO yourself, or even if you are using Auto ISO, you may want to verify that an appropriate shutter speed is being selected.  For example, I found that with the Canon 7D, Auto ISO often selects a much slower shutter speed than what is best for a situation.  Press the shutter button half way down and check the shutter speed.  If it is anywhere from 1/100 to 1/250 or higher, you are fine if your subject isn’t moving.  If the subject is moving, make sure the shutter speed is 1/250 to 1/1000.  If it is any higher or lower than the range you want, you should adjust the ISO until the shutter speed it falls into that range (raise the ISO, keep the aperture the same, and this should result in the camera selecting a faster shutter speed setting).

Focus on your subject using the focus mode of your choice, and take the photo.  Preferably, use single point focus mode and select the focus point you want, so that you have complete control over where the camera focuses.  If the subject is a person or animal, focus on the eyes or eyebrows.  If it is something else, focus on what you want to be sharpest in the photo.

A good book to read to continue learning about this is Understanding Exposure by Bryan Peterson (Third Edition).  Click on the link to see it on Amazon.  It is geared towards photographers just learning about apertures, shutter speeds, and ISO, and helps to explain the concepts better than most other guides.

Let me know how the photos come out! Note in the first photo above that dramatic depth of field can be used to make the foreground blurry as well, not just the background.

Continue reading Mastering Depth of Field.

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