This series of articles is excerpted from Rocky Nook’s Enthusiast’s Guide to Exposure by John Greengo covers the controls — shutter, aperture and ISO.
Mechanical shutters have been a part of photography since the very beginning, when the “shutter unit” was a lens cap or a hat in front of the lens. With modern digital cameras, a new option has arisen: The electronic shutter. This new system will transform the way cameras are made and operated.
An electronic shutter isn’t really a shutter at all — it’s simply a sensor that can turn on and off very quickly. Doing away with the traditional shutter will save money, weight and space. This complex apparatus sometimes causes blurring when the shutter unit opens so quickly that it causes a vibration throughout the camera at the moment the light is recorded by the sensor.
In theory, an electronic shutter is very simple. Turn all the pixels on to record the light striking them, then turn them off a fraction of a second later. With current technology, this process is not so simple. The most common sensor in today’s cameras is a CMOS (Complementary Metal Oxide Sensor), chosen for its high resolution, low noise and efficient use of power. The CMOS doesn’t record light with a simple on/off system. The CMOS uses a sequential system in which it turns on one pixel, then the next one in that row, and so forth until it gets to the end of the row and moves on to the next.
This scanning process results in moving objects being slightly distorted. Moving cars look like they are leaning forward or backward depending on their movement. Cameras that are moved sideways will record buildings and trees that are leaning strongly to the left or right. There are many cameras on the market right now that offer the option of either electronic first shutters or full electronic shutters. Because of the problem with moving subjects, these shutters are usually best employed when photographing stationary subjects. The main reasons to use an electronic shutter are for the silent, vibration-free operation or for reducing exposure time with stationary subjects.
New possibilities arise when using truly silent shutters or those that may have the very slight sound of the aperture closing down. Think about photographing in situations where any noise could be considered a distraction, like a stage play, a courtroom, or when photographing wild animals.
Vibration from shutter movement or shutter bounce is not a rampant or significant problem, but it can affect photographs of subjects with very precise setups, like those common in macro or astrophotography or shots with very high megapixel cameras. With an electronic shutter, there are no moving parts — thus there is nothing to cause a vibration when the shutter unit opens up. This problem seems to peak in significance when the camera is on a tripod and set to a shutter speed around 1/8s. The shutter unit quickly opens up and causes the entire camera to vibrate for a short period of time, resulting in a photo with a slight blur. A silent shutter completely solves this problem.
While the modern sensors can’t turn all the pixels on and off simultaneously, some can do it with a scanning process resulting in shutter speeds of 1/16,000 and 1/32,000, which are faster than the modern mechanical shutters can muster. At these very high shutter speeds, each pixel is turned on for a very short amount of time, but the scanning process across the sensor takes about 1/20s. It’s for this reason that the electronic shutter speeds are not useful for moving subjects but are quite practical for stationary ones.
If you were to shoot in bright sunlight with a low ISO and a wide aperture of f/1.2, your resulting exposure may require a shutter speed of 1/16,000s to 1/32,000s. Most standard cameras will have a top shutter speed of 1/4000s to 1/8000s. The solution, with a traditional mechanical shutter, is to stop the lens down to f/2 or f/2.8, or to use a neutral density filter; both solutions may have a negative impact on the final photo. With an electronic shutter you can select 1/16,000s or 1/32,000s and get the shot without stopping the lens down or adding a filter.
I have no doubt that we’ll see more advanced electronic shutters in the future. Eventually this technology will get faster, or a new type of sensor will be introduced to solve the current problems. The only problem with having only electronic shutters in all cameras is the loss of that traditional “click” sound with each exposure. You’ll need to decide whether you’d prefer a silent shutter or one with a digital “click” sound effect added.
Read excerpts from other Rocky Nook Enthusiast’s Guides.