For many, a photograph where the subject is sharp while the background is completely out-of-focus is what they consider an “advanced” photograph that can’t be done with consumer cameras or lenses, the effect just makes the subject pop out of the frame.
Many people assume that you’re required to own either a long telephoto lens or a very wide aperture lens in order to do so.
This tutorial is for beginners or for those who haven’t bought an expensive telephoto lens or wide aperture lens.
That premise is partially correct, owning either or a combination of those two lens features will give you that look you’re after, but without the knowledge of how it is achieved, you’ll be spending needlessly for something that may be done with your existing equipment.
You can get a blurred background with a sharp subject even with a point-and-shoot camera or your DSLR’s standard kit lens as long as you understand the physics involved. The only difference is, with longer and faster lenses, you can induce more blur than basic equipment. Once you understand why and how to “separate” the background from the subject by controlling depth-of-field, you can apply this knowledge to other forms of photography like macro, still-life, etc. regardless of camera type.
By definition, depth-of-field (DOF) is the area from front to back where the scene is acceptably sharp. Areas that are no longer sharp are known to “fall out” of the DOF. The larger the lens opening (aperture), the shallower/thinner the DOF, the smaller the lens opening, the deeper the DOF – with all else being equal. Controlling DOF means to control how much of your subject should remain sharp.
If you refer to the photos below, aperture controls how much of the scene stays within acceptable focus. Compare the sharpness of the two power fuse boxes in the background with the blue labels.
The first photo was shot with a large aperture (f/2.8), the area of acceptable sharpness doesn’t go beyond the incense holder, rendering a blurry background as those elements fall out of the DOF. The second photo was shot with a small aperture of f/25, the DOF extends about 4ft behind the incense burner and more details can be seen in the background. The two photos are shot at identical distances from the camera.
While aperture controls how much your DOF has, the distance of the background in relation to the subject and camera plays a big role as well. Check out the next two photos. Even at f/32, the second image fails to render the pier cranes sharp as the background is too far off (about 4km away). Even with modest aperture opening of f/3.5 in the first photo (typical consumer lens maximum opening), the background is virtually detail-less due to the distance factor.
The illustration below pretty much explains everything. Keep the camera close to the subject while keeping the background as far away to the background as possible to get the blurriest background possible.
The top diagram will result to a blurrier background because the subject is farther from the background, while the bottom diagram will produce a rather much sharper background in relation to the subject.
In addition, if you double your focal length (20mm to 40mm, 40mm to 80mm, etc.) while doubling the subject-to-camera distance as well (10ft to 20ft, 20ft to 40ft, etc.), you’ll get the same DOF as well.
The series of photographs below are all shot at an aperture of f/4, which isn’t considered as a large opening for lenses and is usually available for most cameras and consumer lenses. With the photos below, take note on how the background (beyond the steel orb) looks.
Image 1 – Focal length 24mm, f/4 – Subject (round object) was about 5 feet from the lens.
Image 2 – Same settings as above, 24mm @ f/4 – Subject was positioned at the lens’ minimum focus distance of 1.5 feet. Notice the much blurrier background, even at a wide-angle, f/4 setting.
To induce more background blur, we can zoom into 50mm and try the same techniques above:
Image 3 – Focal length 50mm, f/4 – Subject about 5ft from lens.
Image 4 - Focal length 50mm, f/4 – Subject at minimum focusing distance. By using a longer focal length, our DOF gets thinner, hence we get more blur.
At maximum zoom 105mm f/4 shot at minimum focusing distance, the effect is maximized (for this particular lens).
Take note, however, that even at 105mm f/4 settings, if you increase the distance between the subject and the camera, the DOF will shift and we’ll get more area in focus. The photo below has the exact same setting as the previous image, but I moved back several feet.
As mentioned previously, this effect is best if either a wide aperture or a long lens is used (or a combination of both a long lens with wide apertures) such as:
Canon EF 200mm f/2.0L IS USM @ f/2.0
Canon EF 85mm f/1.2L USM II @ f/1.2
Canon EF 70-200mm f/2.8L IS USM @ 200mm f/2.8
The images above created lovely separation between the subject and background and the results are really pleasing, but the cost of the lenses above are quite high and may not be feasible for most users.
Don’t fret, you can still get nice background blur with cheaper alternatives such as the ones below.
Canon EF 50mm f/1.8 II @ f/1.8 – $80
Vivitar 200mm f/3.5 manual focus lens from the 1980′s (and other equivalents) – $50 up
Fujinon 55mm f/1.9 manual focus lens from the 1970′s (and other equivalents) – $10 up
If you’re a point-and-shoot camera user, just zoom in a little and activate your macro mode!
One last and important note, pick neutral backgrounds with minimal details to produce a pleasing, non-distracting background. Picking backgrounds with high amount of details (such as a crowded street, wall plastered with ads, etc.) will reduce the impact of background-to-subject separation.
So before assuming that “my kit lens can’t do that, I need new lenses!”, understand that your kit lens and pocket camera can give you the look you want for your portraits if you follow the simple physics behind it.
But if you do have the budget, go treat yourself to a high-end lens :)