Leaving the Shutter Open...

I breifly mentioned the two available choices for controlling the light that falls on a sensor in an earlier blogpost here. Lets dig in to the shutter speed settings and what it can do for your photos?

Leaving the shutter open for longer period means more light gets a chance to illuminate the sensor of your camera. As many cameras allow you to open the shutter for as long as 30 sec or even more, this could be a solution to any low light photography scenario except that it has certain limitations. We'll come to that in a second but let me introduce you to the terminology of slow and fast shutter speed. Fast shutter speed means that shutter opens and closes very quickly hence the exposure time is very small (generally 1/100 of a second or less). Slow shutter speed means that shutter is moving slow and there is more time between shutter opening and closing (generally 1/30th of a second or more). The terms exposure time, shutter speed and shutter opening are different terms defning the same thing - a period of time.

Now, as this period of time gets longer (shutter is slow), certain issues creep in to the photo - related to motion artifacts. These are basically of the following two type:

1. Any motion/shake of the camera will cause the image of the object to move on the sensor (sensor is in the camera so moving camera means sensor is moving relative to the subject). This produces blur in the image which is in general not desirable. Mounting the camera on a tripod or resting it on a table/other objects usually is a solution for this problem.

2. Any motion of the subject will again cause the image on the sensor to move resulting in blurry image. This is where the photographer has little control. Images of people can not remain sharp at shutter speeds of less than 1/20th of a second. Motion artifacts will be unavoidable. Shooting stationary objects, however, is not problamatic. Have a camera mounted on a tripod, and you can take a 30 second shot of a building. It will remain sharp and nice!

Now, in some cases, the blur is desired and shutter speeds are lowered intentionally to get the blur. This slow speed in conjunction with camera or subject movement can create wonderful results. Examples are, a water spring where flowing water becomes cloudy, a moving vehicle headlights and breaklights show streaks of lighting, stars in the night sky become arcs and many more. Or in case of moving the camera with subject to keep the subject sharp while blurring the background (generally referred to as panning). We have seen all these elements as part of some great photographs. So, when used correctly, the blur of a slow shutter can be used to our advantage. For most of the portrait work, however, motion artifacts take away the sharpness of the images and are generally undesirable.