Trick Shots: Low Light

While recently critiquing the work of one of my students, I noticed that several of his images lacked sharpness, which I immediately attributed to camera shake. We looked at the images’ EXIF data to find out at what shutter speed he was shooting while using a 200mm lens. He had been shooting at 1⁄30 sec.—far too slow a shutter speed to use with a telephoto, particularly without the camera being mounted on a tripod. When I asked him why he didn’t increase the camera’s ISO for a more reasonable shutter speed, his response was an all too common one.

Understanding Noise
It’s important to understand what noise is. Each camera sensor, whether a CCD or CMOS, is made of light-sensitive diodes or pixels, which convert light (photons) into a digital signal that’s then saved by the camera as a photographic image. Each of these diodes, when electrically charged, has a certain base level of noise called the “noise floor.” The greater the amount of light that a sensor receives above the noise floor, the less noise appears in the photograph.

Pixel size also plays an important role in the presence of noise, which is why D-SLRs, with their larger pixels, provide less noise than compact cameras, even those sharing the same resolution. Larger pixels result in better light-gathering capability and, thus, reduced noise.

So, when light levels are low, the risk of noise increases. Taking on the appearance of multicolored specks, noise is easily seen in areas of uniform color like a blue sky. Noise also can be viewed in the red and blue channels of a digital image.

As you raise the ISO, noise increases in a way similar to the noise (static) you hear when raising the volume on your car stereo. Other factors, including heat and the length of time a sensor remains charged, impact the presence of noise. There are justifiable reasons to use a high ISO despite this increase, however,

By raising the camera’s ISO setting, you’re increasing its sensitivity to light, which enables you to use a faster shutter speed and make a sharp picture. This is one of the biggest reasons I regularly use high-ISO settings.

Low-Light Shooting
I’m often hired to photograph live performances of musicians, dancers and actors. It’s challenging work, particularly because I don’t have the benefit of controlling the lighting. Prohibited in the use of flash, I have to make the most of the existing stage light, which wasn’t designed with the photographer in mind.

Stage lighting, even at its best, doesn’t provide enough light to shoot at low ISOs, such as 100 or 200. Such a low ISO may result in shutter speeds of 1⁄15 sec. or slower, even when using zoom lenses with a fast maximum aperture of ƒ/2.8. Not only will shooting at such low ISOs result in soft images due to camera motion, but the subjects also will be blurred because the shutter speed is insufficient to freeze their movement.

The choice to increase ISO to 800, 1600 and higher is an easy one for me. I need to get the shot, and I’d prefer to have a “noisy” image that’s sharp than a noiseless image that’s soft. The former can be fixed later. The latter results in yet another useless image.

All of the images illustrating this article were shot at an ISO of 800 or higher. The quality of the files was excellent, even before using a noise-reduction application. This is a testament to the camera makers who have made great strides in both the design of their sensors and the image-processing software incorporated into their cameras.

In many of these images, even an ISO of 1600 didn’t offer me as fast a shutter speed as I would have liked, particularly when using a fast 70-200mm lens. I was sometimes forced to shoot at 1⁄125 sec., which was viable only because of the lens’ image-stabilization feature. But even though the lens’ IS technology could counter problems with camera motion, it couldn’t help me with the movement of the performers.

It was dependent on me to capture moments when a telling gesture was at its peak. It’s a challenge, but one that’s made easier by the fact that my camera was set to perform optimally under difficult lighting conditions.

By increasing the camera’s ISO, using the fastest shutter speed possible and carefully handholding my camera, I could get consistently sharp results. Though there were certainly images that were soft, I succeeded in producing a greater percentage of photographs that met my criteria for quality.

The Importance Of Exposure
Exposure is always important when photographing, but it’s especially essential when shooting under low-light conditions and high-ISO settings. Underexposed images increase the presence of noise, especially when you attempt to correct for it in Photoshop. Pulling out shadow detail from an underexposed shot often only succeeds in making the presence of noise more obvious.

So, it’s important to obtain as accurate an exposure as possible, and few things are better for achieving this than the camera’s histogram. This graphic representation of image tonal data, from the brightest white to the darkest black, is a great reference for knowing whether you’re risking increased noise because of severely underexposing your images.

To avoid blowing out the highlights, some photographers will lock in a -1⁄3 or -1⁄2 exposure compensation on their camera. This can be a real drawback when shooting under low light at high ISOs, however, resulting in images more underexposed than necessary. By referring to the histogram, you can make a more concise assessment of lighting and exposure, ensuring that you maintain maximum highlight and shadow detail.

For photographing performances, I’ll shoot in manual mode. Automatic exposure modes, such as aperture priority and shutter priority, can be unduly influenced by dark and light elements in the frame. This results in shifts of exposure that can diminish image quality. As I’m often photographing scenes in which the background falls into deep black because of light falloff from the stage lights, the camera can be easily fooled into using a longer exposure than is necessary, risking overexposed images. By sticking to manual, I avoid such problems and ensure consistently exposed photographs. If the lighting changes, it’s a quick thing to take a test shot, evaluate my histogram and make any necessary adjustments.

Exposure is also important if you’re shooting time exposures, though you also have the benefit of in-camera noise reduction, which reduces the presence of noise while the sensor remains charged for lengthy periods of time. The drawback is that this requires longer processing times, an issue that’s often unacceptable when shooting performances. For nightscapes, however, engaging the camera’s noise-reduction feature is a good choice.


Noise-Reduction Software
Reducing the presence of noise in digital files after the fact has been made easy by a host of applications, which attempt to strip the noise from the image while maintaining image quality. While Adobe Photoshop and other image editors include some level of noise reduction, there are many third-party plug-ins that offer a myriad of ways of eliminating noise. Alien Skin Image Doctor, Auto FX AutoEye 2.0, Imagenomic Noiseware, Nik Software Dfine and PictureCode Noise Ninja, are just a few of the applications that can evaluate a file and separate noise from the actual image data.

These applications often do a remarkable job at reducing noise, but there’s often a slight loss in overall sharpness that results. However, all these applications provide fine-tuning features that allow you as the photographer to have complete control over how subtle or aggressive the noise reduction will be. 

Though noise is certainly something to be aware of, the benefits of high ISOs can prove worthwhile, especially when it comes down to getting the shot or not.