Sometimes Blur Is a Good Thing
Geoff Cronje used panning another way in this image. Here the shutter speed is a mere 1/180th of a second. He kept the plane in the same location in the viewfinder and turned the background into a blur. Since the plane was not moving on the sensor, it stayed sharp. The camera was moving in relation to the background. It’s the same effect we see if we fix our vision on the side of a moving vehicle.
I took the picture of the actor rehearsing with the boa under stage lighting. A higher ISO and a faster shutter speed, or using a flash, would have let me freeze the image, but I wanted some blur to add movement. Notice how her face and torso are sharp, as is her left arm. Her right arm is blurred and the boa is a swirl of color.
This effect required timing. Her movements varied as she pivoted around and twirled the boa. As with the groom and his men in the picture below, there was a point at which she was almost still, and the boa was moving quickly. That’s when I pressed the shutter. It was open for 1/40th of a second. The landscape by Johan Aucamp makes use of selective blur as well.
Here the exposure was one second at f/7.1. The long exposure turned the moving water into a silky cascade. Cutting that time in half would have blurred the water, but not provided the almost misty effect. A fast exposure would have frozen the waterfall and the flowing stream would have looked clear. The exact shutter time needed for these water effects will vary from location to location. That’s because the distance and direction relative to the camera will change, and so will the speed of the water. In some cases you may want a very slow shutter speed, maybe several seconds. With open sun, or even bright shade, that may require either a polarizing or neutral-density filter to allow that interval. The polarizer is a great tool for water-related photographs. It lets you adjust the highlights of the reflections on the surface.
A Note About Flash
The flower petals below are suspended in mid-air, and the couple is perfectly sharp, even though the photographer used a slow shutter speed, only 1/15th of a second. Flash can change the rules. Remember that the actual exposure is based on the amount of light reaching the sensor. The flash used for this picture was much brighter than the available light, and flash is very fast. Its duration varies with the model and settings, but it is less than 1/1000th of a second and often much less than that. Some units can fire within 1/25,000th of a second. As you can see, flash can dominate a weaker light source. Sometimes the ambient light level is close to the power of the flash. Then using a slow shutter speed can result in blurring. If the flash is too powerful, both shadows and the background of the scene will be very dark. It’s worth the time to practice using flash with different shutter speeds.
Your DSLR has a flash synchronization (sync) speed. This is the fastest shutter speed that can be used with a flash under normal conditions At speeds faster than the sync speed, the shutter opens to just a narrow slit, and the flash duration is too brief to allow the light to reach the entire surface of the sensor. Your flash may be able to fire a rapid series of bursts during the exposure to allow faster speeds in a special operating mode. It’s worth taking the time learn about your camera’s sync speed and experiment with high-speed options. Now that you’ve been properly introduced to the shutter, consider some self-assignments, and experiment with both freezing motion and inducing blur.