I shared a pair of weasel images (Curious Weasel, Weasel Carrying Ground Squirrel) captured while hanging out with (mostly waiting for) a pair of weasels in Rocky Mountain National Park. One of my favorite aspects of these images is the strong background blur that makes the subject boldly stand out.
While many of you following this site might find this advice basic, the basics are important, especially for those starting out, so let's talk about some background blur basics today.
1. Get Closer to the Subject
Moving closer requires a shorter focus distance. The shorter focus distance takes the background out of focus, increasing the blur.
2. Position Against a More Distant Background
Positioning the camera and lens so that the background is farther from the plane of sharp focus increases the blur. Orienting the shooting position to avoid the closer background trees, rocks, buildings, etc., makes a more significant blur happen.
3. Use a Longer Focal Length Lens
A longer focal length increases the magnification of the background details, which increases the blur.
4. Use a Wider Aperture
A wider aperture creates a shallower depth of field. That effect increases the background (and foreground) blur.
5. Use a Camera with a Larger Imaging Sensor
A full-frame camera takes in a wider angle of view than an APS-C model using the same focal length lens. A wider angle of view requires a 1.5x (Sony) or 1.6x (Canon) longer focal length or a position considerably closer for the subject to remain the equivalent size in the frame. Both of those options are already on this list.
Today, the interchangeable lens most adept at blurring the background is the Sigma APO 200-500mm f/2.8 EX DG Lens set to 500mm f/2.8. However, a reality check after looking at that behemoth's price and specs (B&H | Adorama | Amazon) leads us to consider the second most background blurring capable lens. The next best choice is one of the 600mm f/4 options.
While not small or inexpensive, the 600mm f/4 lenses reward the owner (or renter) for their expense and carrying effort by creating differentiation in their photos. A 600mm f/4 lens on a full-frame camera, such as the outstanding Sony FE 600mm f/4 GM OSS Lens and Sony Alpha 1 Camera combination used for this example can melt the background into a pleasant color blur. That blur can make a subject pop from even a busy, distracting environment.
Keeping small subjects such as the weasels relatively large in the frame makes the getting close blur aspect happen by default. Of course, keeping these hyper little creatures in the frame at this distance is quite challenging. Fortunately, I guessed right at this time, being in the ideal position when the weasel paused to look around.