Long exposure photography is useful for creating a blur effect with movement (think waterfalls and cityscapes with cars) and necessary in low light such as with night photography. Of course your shutter speed, which may vary from a few seconds to minutes, will vary based on the amount of ambient light, and use of a neutral density filter (which I will discuss below). This article will give you tips for taking long exposures, whether during the day or at night!
First, a sturdy tripod is critical and minimizing movement in any way possible. With shutter speeds even a few seconds long, any attempt to hand hold the camera will result in so much motion blur, the image will be terrible. The tripod should not only be sturdy, but in windy situations consider anchoring it with your camera bag, or making sure the tripod legs are secured well to the ground. Consider using the mirror lockup feature to reduce camera vibration and a remote shutter release or shutter timer to further reduce any movement related to your hand touching the camera.
With long exposures, your camera’s shutter is obviously held open much longer than a “normal” exposure. A thousand pictures shot with a shutter speed of a 1/1000th of a second has kept your aperture open only a second. I’ve shot night pictures with 4 or 5 minutes of exposure time. Even though you may take fewer total pictures, you’ll drain battery quickly.
Aside from minimizing camera motion, you also want to reduce digital noise as much as possible. No, you don’t have to be quiet! Digital noise is the graininess that you see in pictures, usually in darker areas. If you look carefully at areas of black in a darker image, you will see tiny dots of other colors. That is digital noise and increases more quickly at higher ISO levels. Therefore, particularly for night photography with long exposures, try to keep your ISO as low as possible. Of course, this will increase your exposure time but it will be worth it, particularly if you plan to create large copies of your image. More advanced Canon digital SLR cameras have a built in function for reducing long exposure noise, remember to turn that function to maximum!
Neutral density filters are generally necessary for outdoor daylight shooting where ambient sunlight means getting an exposure time greater than even a fraction of a second is difficult even with a tiny aperture and low ISO value. A neutral density filter is simply a filter that blocks light from entering the lens. Unlike graduated filters, a neutral density filter uniformly blocks light. Think of them like a sieve (or filter!), allowing less total light to hit the camera’s sensor thereby increasing the time the camera’s shutter needs to remain open at any given aperture to produce a correct exposure.
Neutral density filters (or ND filters) have somewhat of a bizarre numbering system. Each “stop” on a neutral density filter is considered 0.3 but I’ll be honest, I’m not sure why. A 3 stop ND filter is therefore 0.9, and a 10 stop ND filter is labelled as 3 (that can be confusing). Each stop halves the amount of light entering the lens, doubling the length of time the shutter remains open. So a 3 stop ND filter will lengthen the shutter speed by a factor of 8 (2 x 2 x 2), and a 10 stop ND filter will lengthen the shutter speed by a factor of approximately 1000! (2 to the 10th power is 1024). I carry both a 3- and 10-stop ND filter and probably use the 10-stop one more.
Unfortunately, lenses come in different sizes and ND filters don’t grow on trees. Some, particularly the better brands, like B + W, can be quite expensive. One trick is to by a few step-up rings so that you can use the same neutral density filter on all your lenses, even if the front of your lenses are different sizes. The step-up rings are much cheaper than even cheap filters!
Since using a 10-stop ND filter is somewhat of a challenge (because it can “trick” your camera), I’ve dedicated a separate article to walking you through the necessary steps.Tags: Equipment, Neutral Density Filter, Photography Tips, Shutter Speed