5. Minimum Sustaining Shutter Speed
This is a simple issue, and more of a tip, when it comes to working with and even purchasing lenses. Minimum sustaining shutter speed refers to the slowest shutter speed one can handhold a lens and maintain focus. Any shutter speed slower may incur camera shake and potentially ruin an otherwise great shot (Figure 1.9). When shooting with shutter speeds slower than the minimum sustaining shutter speed, it is best to stabilize the camera by placing it on a monopod, tripod, or anything solid. So, how do you determine minimum sustaining shutter speed? The two determining factors are focal length and your own personal stability.
Figure 1.9 This shot of a gray fox is out of focus due to my inability to handhold the 300mm lens I was using at 1/250 of a second shutter speed, just a bit slower than the lens’s minimum sustaining shutter speed.
ISO 160 • 1/250 sec. • f/4 • 300mm
The first factor is the most technical and worth keeping in the back of your mind. The minimum sustaining shutter speed is the shutter speed that has a denominator (since shutter speeds are measured in fractions of a second) that is closest to the focal length in which you are shooting. For example, let’s say you are shooting at 100mm. Theoretically, a shutter speed of 1/100 of a second is your minimum shutter speed—the slowest you could shoot before your own body shake forces the image out of focus. For a 24mm focal length, 1/30 of a second might work best. For a much longer focal length, such as 400mm, 1/500 of a second might sustain focus.
A minimum sustaining shutter speed also has a lot to do with your own stability. With experience and technique, and a better sense of balance, some folks can shoot with much slower shutter speeds than those suggested above. When I’m locked in a stable stance, I feel fairly comfortable shooting a 24mm lens, and especially a 16mm lens, at 1/15 of a second. Test your stability while practicing at different focal lengths, slowing your shutter speed down for any given focal length until you notice a big difference. Sometimes you can feel it, but it is best to run through a range of shutter speeds while focusing on the same subject and then review the files on a computer screen. Keep practicing, and your minimum sustaining shutter speed will lower.
Image Stabilization (IS) is a feature of many lenses in the Canon lineup (Figure 1.10), allowing photographers to shoot with slower and slower shutter speeds. Lenses with IS—such as the EF 70–200mm f/2.8L IS and the EF 70–300mm f/4–5.6 IS—contain a mechanism that shifts the optics in a way that stabilizes the unsteady hands of the shooter, especially for precarious shutter speeds. In some cases, Canon Image Stabilization claims four stops worth of IS, an amazing amount of stabilizing when you’re in a pinch (Figure 1.11).
Figure 1.10 Image Stabilization logo on an EF 70–300mm f/4–5.6 IS
Figure 1.11 It is fairly common to place a camera and lens on a tripod to shoot macro work. Macro lenses with Image Stabilization help alleviate camera movement, allowing many to handhold these tight shots.
ISO 100 • 1/80 sec. • f/2.8 • 100mm macro
There is no rule stating you must shoot at the minimum sustaining shutter speed. In fact, you should shoot with as fast a shutter speed possible given your aperture and ISO. However, some moments call for shooting with slower shutter speeds, and when they do, it is worth knowing where your minimum sustaining shutter speed exists for the focal length in use.