Night Scene Mode
A camera's Night Scene mode is built to take landscape or cityscape shots when there isn't a lot of natural light. It usually demands the use of a tripod: Depending on the camera, the Night Scene mode may use a slower shutter speed, meaning that you'll get a blurry image if you try to steady the camera with just your hands.
We weren't pleased with our Auto-mode results. The camera boosted the ISO to 800, shifted the aperture to a wide-open f/2.0, and used a fairly fast shutter speed of 1/15 of a second. Color accuracy and fine-grain details suffered at those settings. The camera also fired the flash, which illuminated the post in the foreground and caused light to reflect off the mist in the sky back toward the camera.
The results from Night Scene mode were surprisingly disappointing. Although the camera properly adjusted the shutter speed downward to half a second and used a lower ISO of 160, the flash still fired while the aperture stayed at f/2.0. The resulting image closely resembled the one taken in Auto mode.
Our night-landscape manual settings produced some of the most dramatic differences we saw across all of our test shots. We turned the flash off to avoid illuminating the post in the foreground and having the mist reflect light. Next, we tried to improve the detail by dialing down the ISO to 100 and using a very slow shutter speed of 6 seconds. The slow shutter also made the surface of the water look smooth, while the lower ISO made colors seem more accurate. The slow shutter let us close the aperture to f/5.6, deepening the depth of field while still capturing plenty of light for a well-exposed image.
Night Portrait Mode
Although it sounds similar to Night Scene mode, Night Portrait mode is a different animal altogether. It's designed for capturing evenly exposed shots of a person standing in front of a nighttime background. Executed well, a night portrait will let viewers see detail in both the person and the dark background. It's a useful scene mode for vacationers, since it's ideal for taking nighttime photos of family and friends in front of landmarks.
Cameras handle this mode in various ways. Most commonly, the flash fires to enhance detail in the foreground, while the camera slows its shutter speed to capture a detailed, naturally lit backdrop. Other cameras turn off the flash and take several shots in rapid succession at different exposure levels, and then combine the images to create one evenly exposed shot; the camera uses overexposed images to highlight details in dark parts of the scene and more evenly exposed images to highlight details in lit areas. In both flavors of Night Portrait mode, a tripod or flat surface is handy, and sometimes a necessity.
In our test night portraits, Auto mode had a hard time capturing details in the background. Because the flash was too powerful and the shutter speed was a bit too fast (1/30 of a second), it illuminated the subjects well but eliminated many of the background details. For example, the "Pier 28" sign on the building is unreadable in our Auto-mode shot.
The PowerShot S90's Night Portrait mode fires the flash, opens the aperture to f/2.2, and slows the shutter to 1/8 of a second. In our photos it was much better than Auto mode at highlighting foreground and background details, and the "Pier 28" sign is clearly legible. The camera also used a higher ISO of 500 to brighten up the building and the bridge in the background, which were well out of range of the flash.
On our manual shot, we used the flash to illuminate the subjects, but we reduced the ISO to 320 and slowed the shutter speed to 0.6 second to capture background details while preventing image noise. We also closed the aperture to f/5.6 to make background details more visible, but you can't see much of a difference in depth of field between our manual shot and our scene-mode shot; the effects of aperture adjustments are more pronounced in DSLRs and other large-sensor cameras.
In our manual shot, we especially liked how the aperture setting surrounded the streetlights in the background with a star-like pattern. You can achieve the same effect by using smaller aperture settings when shooting any bright lights.
Employing a bit of skill and creativity with your flash can help make Night Portrait mode more effective: If your camera supports it, you can dial down the flash intensity to avoid overexposing your subjects, or even put a piece of tissue paper or cloth in front of it to weaken its overpowering effects.
Next: Sunset and Fast-Action Modes