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Canon Powershot S70

By: Dave Etchells

With the same wide angle lens as its predecessor, the S70 boosts resolution with its 7.1 megapixel sensor, but holds the line on image noise.

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Page 6:Exposure & Flash

Review First Posted: 9/30/2004


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The PowerShot S70 offers excellent exposure control, with Automatic, Program AE (P), Shutter Speed Priority AE (TV), Aperture Priority AE (Av), Manual (M) exposure modes, and a handful of special settings for specific shooting situations. Under the Automatic exposure mode, the camera controls both shutter speed and aperture settings, but lets the user control the Flash, Macro, Digital Zoom, Drive Mode, Compression, and Resolution settings. The Program AE mode also controls shutter speed and aperture settings, but also provides access to other exposure controls not offered in Auto mode, including Exposure Compensation, Flash Exposure Compensation, Spot Metering, ISO adjustment, AE lock, Auto Exposure Bracketing, White Balance, Contrast, Sharpness, and Color Saturation.

Shutter Priority mode puts you in control of the shutter speed setting (from 1/2,000 to 15 seconds ), while the camera chooses a corresponding lens aperture. At apertures wider than f/4, it's important to note that the camera is only capable of 1/1,250 as its maximum shutter speed. As with the Program AE mode, you maintain control over all other exposure options. Aperture Priority works along similar lines, except that you control the aperture (f/2.8 to f/8.0) and the camera chooses the best corresponding shutter speed. Both the shutter speed and aperture values are displayed on the LCD monitor. If the camera can't find an aperture or shutter speed to produce the correct exposure with the shutter speed or aperture you've selected, the LCD indicators will turn red, letting you know that you need to change the setting you selected. A Custom (C) mode lets you save a (wide) variety of exposure settings previously saved in any of the P, Tv, Av, or M exposure modes, including menu settings, zoom position, and manual focus. Once saved, the exposure settings automatically come up when you enter Custom mode.

As just mentioned, in all exposure modes, shutter times faster than 1/1,250 are only available at apertures of f/4.0 and smaller. For the record, it's fairly common to see top shutter speeds limited to smaller lens openings, as the shutter speed limit becomes a function of how long it takes for the shutter aperture to transit the light cone of the lens, which is itself governed by the size of the lens' aperture.

A number of preset "scene" exposure modes are also available for shooting under special conditions. These modes preset a variety of camera options, letting complete novices capture decent pictures in challenging situations without having to know all the ins and outs of the camera. Portrait mode uses a large aperture setting to reduce depth of field, resulting in blurred backgrounds and strong focal emphasis on the primary subject. Landscape mode uses a small aperture to keep both the foreground and background in sharp focus. A slow shutter speed is also common in Landscape mode, so it's recommended that you use a tripod.

Night Scene mode uses a slow shutter speed to capture the color and detail of evening settings, along with a flash exposure to illuminate the primary subject in the foreground. By using slow shutter speed and the flash together, the overall scene is more evenly exposed. This mode can also be combined with the redeye reduction flash for portraits, or the flash can be turned off. Portrait subjects should be warned though, to stay still after the flash, until the shutter is closed.

Fast Shutter is provided for fast-moving subjects such as sporting events, while Slow Shutter is available for creating a sense of motion in fast-moving subjects. Fast shutter speeds stop action to maintain sharp focus on moving subjects, while slow shutter speeds tend to blur the subject because the shutter stays open longer to record the image. This last effect is particularly striking when used with swiftly moving water such as that found in water falls or streams.

The S70's Effects options have been moved from the Mode dial position to an option under the Function menu (displayed by pressing the FUNC button). The Effects setting provides a choice of six color and image options, including Vivid color, Neutral color, Low Sharpening, Sepia tone, Black-and-White, and Custom. The Custom option accesses Contrast, Sharpness, and Saturation adjustments. Effects are shown on the monitor so you can view the image before taking the exposure.

A quick-review mode lets you quickly confirm the most recently recorded image. To access the Review mode, you simply push the Playback button next to the upper right corner of the LCD to switch to image playback. If you like, you can immediately erase the displayed image by pressing the Manual Focus / Delete button, which calls up a small erase menu on the bottom of the monitor. To return to Shooting mode, press the Replay button to the right a second time, or simply touch the Shutter button. Like most Canon cameras though, you effectively have an "instant" review mode available at any time, simply by holding down the shutter button after you've snapped the picture: The just-captured image will remain on the LCD until you release the shutter button.

Exposure compensation can be adjusted from –2 to +2 exposure values (EV), in one-third-step increments. The camera's metering system offers three operating modes, which include Evaluative Light Metering, Center-Weighted Averaging, and Spot AE Point. Metering mode is selected by pressing the Metering / Microphone button on the left side of the LCD monitor. Evaluative metering divides the image into several zones and determines the exposure based on the position of the subject, image brightness, ambient light, direct light, and backlighting. Center-weighted averaging is based on an averaged light reading of the overall scene, but places more emphasis on the center of the viewfinder or LCD monitor. Spot metering reads only a specific point in the viewfinder. Through the Record menu, you can choose to base the spot reading on the center of the frame or the adjustable autofocus frame, which you can position anywhere within the central ~60 percent of the image area.

Another high-end feature brought over from Canon's G-series digicams is independent exposure lock. With most digicams, you can lock both focus and exposure by half-pressing and holding the Shutter button prior to the shot itself. This can be very handy for off-center subjects. Sometimes though, you want to lock the focus on one part of the subject, but set the exposure based on a different part. On the S70, this is accomplished by half-pressing the Shutter button (which will set both focus and exposure), and then subsequently pressing the Metering/Audio button at bottom left, to reset the exposure. Of particular note, this option works for flash exposures as well, whenever the flash is enabled. Very slick.

The S70 offers nine White Balance modes, including Auto, Daylight, Cloudy, Tungsten, Fluorescent, Fluorescent H (daylight), Flash, Underwater (for use with the optional underwater case) and Custom. The Custom mode allows you to manually set the white balance by holding a white card in front of the camera and pressing the Metering / Audio button to set the value. You can now save two separate Custom white balances, so that you can quickly switch back and forth without having to reshoot a white card. This is extremely useful for a party situation, where you may be moving in and out of different light sources.

ISO film speed equivalents on the S70 are set in the Function menu, with choices of Auto, 50, 100, 200, and 400. The higher the ISO setting, the more you can extend the camera's exposure range in low-light situations. Just keep in mind that higher ISO values have progressively lower quality levels, with increased image noise.



The S70's built-in flash operates in one of five modes: Auto, Red-Eye Reduction (Auto), Red-Eye Reduction (Flash On), Flash On, and Flash Off. The Auto mode tells the camera to determine when flash is necessary, based on existing exposure conditions. Flash On means that the flash fires with every exposure, regardless of lighting conditions, and Flash Off completely disables the flash. The two redeye reduction modes fire a small pre-flash before the full flash, to reduce the redeye effect in portraits. The difference between the two redeye modes is that the auto mode lets the camera decide when to use the flash, while the Flash On mode fires the flash with every exposure. All flash modes are accessed by pressing the Flash / Index button located to the left of the optical viewfinder. A Slow-Synchro mode is available through the Record menu, which combines the flash with a slower shutter speed. The slower shutter speed lets more of the ambient light fall on the camera's sensor, brightening background objects. You can also decide to synchronize the flash with the first or second curtain of the shutter, to control whether motion-blur trails precede or follow moving subjects. (Most of the time, you'll want to use second-curtain sync, so any motion blur will follow behind the subjects, for a more natural look.)

The flash exposure can be adjusted from -2 to +2 EV in one-third-step increments through the Function menu, and flash and ambient light exposure can be controlled separately in slow-sync flash mode. Additionally, you can adjust the flash output to 1/3, 2/3, or Full, through the same Function menu option (in Manual mode or when the Flash Adjust option of the Record menu is set to Manual). This manual flash power control is useful for balancing the light of the internal flash with that from external "slave" strobe units. As mentioned earlier, you can also lock the Flash Exposure (FE) setting for a specific area of your subject, just as you would with a normal exposure. Begin by framing your subject as you would normally, and half-press the Shutter button to lock focus on your main subject. Then, reframe the scene to place the portion of the subject you want to expose for in the middle of the frame. While still holding the Shutter button down, press the Metering / Audio button to lock the flash exposure (an asterisk will appear at the bottom of the screen). The flash will fire a pre-flash to lock the exposure reading, after which you can recompose your image and press the Shutter button all the way down to make the exposure with the FE lock in place. (Note: Pressing any other button after the Metering / Audio button will cancel the flash exposure lock.) Playing with it a bit in the office, I found that the flash exposure lock gave me a tremendous amount of control over flash exposures. This is definitely a feature that will be worth playing with a little if you end up owning an S70.

Canon rates the S70's flash as effective from 1.8 to 14 feet (35 centimeters to 4.8 meters) at maximum wide-angle and 1.8 to 6.6 feet (35 centimeters to 3 meters) at maximum telephoto. In my own tests, it illuminated the test target adequately out to the maximum 14 foot range of my test, but it's clear from looking at its images that it "cheats" a little to get there. As is the case with so many cameras these days though (particularly compact models), the S70 apparently "cheats" a little bit by boosting its ISO setting without informing the user. - Canon's File Viewer Utility software still reports the ISO as 50, but it seems clear from the noise levels my test images shot at 10-14 feet that some sort of boost was applied to the ISO to achieve the longer flash range.

Auto Exposure Bracketing
The Auto Exposure Bracketing (AEB) mode is accessed through the Drive option of the Function menu. It automatically captures a series of three images, each at a different exposure setting. You can manually set the exposure variables in one-third-step increments, from -2 to +2 EV. The camera makes all three exposures with just one press of the Shutter button. Unfortunately, this function cannot be used with flash photography. If the flash fires, only one image will be recorded. (The likely reason for this is that the onboard flash recharges too slowly to be usable in a multiple-exposure application like this.)

Continuous Shooting
The S70 has two Continuous Shooting modes, which are accessed through the Drive option of the Function menu. Standard Continuous Shooting captures multiple, successive still images, at about 1.4 frames per second, providing enough time to display each image briefly after it is captured. High Speed Continuous Shooting captures images at 1.8-2.2 frames per second, as long as you hold down the shutter release. The number of images and actual shot-to-shot speed depend on several factors, including the amount of memory remaining on the flash card and the size/quality of the images being acquired. (Canon rates the two modes at 1.5 and 2.0 frames/second respectively, see the detailed timing results further on in this review for the exact performance numbers I measured in my own tests.)

Movie Mode
The S70 also offers a Movie mode, which is accessed by turning the Mode dial on top of the camera to the miniature movie camera symbol (a camera will appear in the upper left corner of the LCD display). The AVI / Motion JPEG files are recorded at 640 x 480, 320 x 240, or 160 x 120 pixels. At the highest resolution, the camera can record up to 30 seconds of video, at 10 frames per second, while the two lower resolutions permit recordings as long as three minutes, at approximately 15 frames per second. (Naturally, these maximum recording times assume that sufficient space is available on the CompactFlash card.) To begin recording, you simply press the Shutter button all the way down and hold it there until the red circle in the upper right corner of the LCD appears. Once the red circle appears, you can release the Shutter button and the camera will continue recording. To end the recording, press the Shutter button again. The flashing green LED light next to the eye-level viewfinder indicates that the camera is storing the movie. When finished, you can view the recording by pushing the Playback button to the right and depressing the Set button. The camera will play back both moving images and sound. Note that the recording options are largely preset in Movie mode: Image resolution, Self-Timer, Exposure Compensation, White Balance, and Macro and Manual focus are the only adjustable functions. While the lens can be zoomed before and after movie recording, it cannot be activated during the recording process itself, and the camera's exposure is also set and fixed at the beginning of the recording interval.

Stitch-Assist Mode
The Stitch-Assist mode records a series of overlapping images to create horizontal or vertical panoramas, and 2x2-frame rectangular composites. A framing guideline for each format appears in the LCD monitor to help line up successive shots: After each image in the series is captured, a portion of it remains onscreen to serve as an alignment guide for the next shot in the series. This makes it much easier to line up each shot with the ones that went before it. For the panoramas, you can take as many images in a series as you want, enabling you to record a full 360-degree circle of the surrounding scenery if you so desire. The 2x2 mode uses a series of only four images, starting from the top left corner and moving in a clockwise direction, to create a complete composite. Once captured, you can use Canon's included PhotoStitch program to seamlessly combine the images in your computer.

Self-Timer Mode
The Self-Timer is set through the Drive sub-menu in the Function menu. When set to Self-Timer, the camera displays the standard self-timer icon (a clock counting down) in the LCD display, and depressing the Shutter button activates a two- or 10-second countdown (depending on the Drive mode selected), during which a bright amber lamp on the camera's front panel blinks, gaining speed in the last two seconds. If the camera's Beep function is turned on in the Setup menu, you will also hear the beep counting down. The two-second option is very handy when you're shooting long exposures with the camera on a tripod, and want to avoid jiggling the camera and blurring the shot when you press the Shutter button with your finger. The two-second countdown is enough time for any vibrations to die down before the shutter opens, but not so long as to seriously slow your shooting.

Set through the Record menu, the S70's Intervalometer mode lets you record images at set intervals, achieving the effect of time-lapse photography. Shooting intervals range from one to 60 minutes, with a maximum of 100 images in the series (depending of course, on the amount of space available on the memory and the image size and quality settings you've selected). Once you've set the parameters, pressing the Shutter button starts the series. Once the set number of shots has been captured, the camera shuts itself off.


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