Canon PowerShot S20Canon packs 3 megapixels and a 2x optical zoom into their "smallest digicam" body!<<Optics :(Previous) | (Next): Shutter Lag & Cycle Time Tests>> Page 6:Exposure & FlashReview First Posted: 4/4/2000 |
Exposure
We experienced good exposure control on the S20, and appreciated the variety of capture options available, although the tweaky techno-photographer in us yearned for direct aperture and shutter speed control. The relatively straightforward Automatic mode puts the camera in charge of all settings except flash (which you can only turn on or off), macro and the self-timer. Switching into Manual mode gives you control over metering mode (center-weighted or spot), exposure compensation (EV), white balance, ISO, sharpness, contrast, etc. Somewhat oddly, Auto mode doesn't allow you to select different image size/quality settings, but apparently always defaults to Large/Normal quality. The Image capture mode gives you a choice of preset shooting settings, including Landscape, Fast Shutter, Slow Shutter, Night Scene and Black & White. There's also a Stitch Assist mode, which helps you compose panoramic shots. (Stitch assist helps align the separate images that will make up the panorama, and fixes exposure based on the first image in the series. The individual images must subsequently be stitched together in the computer with the PhotoStitch application.)
The S20's manual is rather sketchy on just what the Image capture mode options do. Fast and slow shutter are fairly obvious: Within the constraints of available light, these set the shutter speed to the fastest or slowest available. (As governed by the range of available lens apertures.) Besides the obvious effect on shutter speed (fast shutter for sports, slow shutter for deliberate motion-blurs), you can also use these settings for their effect on aperture (fast shutter = large aperture = less depth of field, slow shutter = small aperture = greater depth of field). Night Scene mode appears to extend the maximum exposure time downward to 2 seconds, and simultaneously adjusts the camera so as to reduce its tendency to blow-out bright foreground objects. Black and White mode is fairly self-explanatory, although it bears mentioning that the monochrome images it produces are still full RGB files, so the file size isn't reduced as you might expect. Finally, we're a little puzzled by Landscape mode, as it didn't seem to have any obvious effect on the image. (The manual just says "for recording broad expanses of scenery".) We expected this would be a mode that biased the exposure system toward smaller apertures for greater depth of field, but this didn't appear to be the case.
The variable ISO is controlled via adjustments available through the Gain setting in the Record menu. Options include zero (ISO 100), +1 (ISO 200) and +2 (ISO 400). Oddly, the boosted ISO values don't seem to contribute to lower usable light levels, but rather just to faster shutter speeds at whatever light level you're currently shooting at. Although you don't have any control over shutter speed or aperture settings, the S20 offers shutter speeds from two to 1/1,000 seconds and aperture ranges from f/2.8-f/4.0 (wide to tele) to f/8.0. (Our unit would only go to two seconds in slow-shutter mode, not in normal or Night Mode. This may have been a defect with our specific unit though.) The camera doesn't report either shutter speed or aperture to you, something we'd at least like to see an option for. Shutter speed appears to vary in approximately 1/2-stop increments, and the lens aperture appears to have about 6 available aperture settings over the range from f/2.8 to f/8.0. (We were a bit puzzled how the camera gets the 1/3 EV exposure increments with aperture and shutter values that vary in 1/2 EV steps. It seems it may actually make fine adjustments with the internal gain setting...) White balance is controlled by a separate white balance button, with options for Auto, Daylight, Cloudy, Tungsten and Fluorescent white values. Through the same button, exposure compensation can be adjusted from -2 to +2 EV in 1/3 EV increments. A 10 second self-timer is controlled by the self-timer button on the back panel and activated when the shutter button is fully pressed (the LED on the front of the camera blinks slowly for the first eight seconds, then speeds up for the remaining two). We appreciated the fact that the control arrangement of the S20 allows the self-timer to be used in the camera's macro mode: This is very handy for reducing camera jiggle when using a tripod or macro stand for macro work.
The S20 also gives you the option of center-weighted or spot metering, via the Set button on the back panel. Center-weighted averages the light readings from a large area in the center of the composition while spot takes a reading from dead center. Spot metering is available only in Manual mode, and then only when the LCD display is being used as the viewfinder. (A small square outline lights up on the LCD display to indicate the exact area being used to calculate exposure from.)
Flash
The S20's built-in flash offers four modes of operation (Auto, Red-Eye Reduction, On and Off) and ranges from 6.7 inches to 10.8 feet (17cm to 3.3m) in wide angle and 6.7 inches to 7.5 feet (17cm to 2.3m) in telephoto. Flash metering is actually performed through the lens, not via a separate sensor on the front of the camera. It's therefore likely to be more accurate, particularly as the lens zooms from wide angle to telephoto.
Continuous Shooting Mode
Controlled by the same button that activates the self-timer option, the S20 features a continuous shooting mode which captures approximately 1.7 images per second, depending on the amount of space on the CompactFlash card and in buffer memory (the interval increases drastically once the buffer fills). In this mode, the camera shoots continuously until the shutter button is released.
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The S20's software includes a very capable image-stitching application that lets you combine multiple images into a single larger one. You can stitch images horizontally, vertically, or even in a 2x2 matrix for "super" resolution. The S20 supports this use through a special exposure mode called "Stitch Assist." When you enter stitch assist mode, the LCD viewfinder turns on and splits into a double display. You can select the direction you want to shoot your pictures in via the left and right arrow keys on the rocker control. Once you snap the first picture, a copy of it remains on-screen, and the "live" portion of the viewfinder switches, so you can see to align the two images with each other. The photos above right show how this works, the first one showing the original image we're shooting, and the second one the screen as we're about to snap the second exposure, with the two images lined up. Overall, this is one of the nicest panorama-assist modes we've seen on a digicam.
Mysterious Purple Problem? - An easy fix!
While we didn't see it to a significant extent it in our own testing, several readers have written in to report a tendency in the S20 to produce rather purplish skies. (We apparently missed the problem on our first go-round because we'd just switched to version 5.5 of Adobe's Photoshop(tm) for our picture analysis, and the color-management settings in v5.5 masked the problem to a large extent. - Thanks to reader Greg Sullivan for helping us track down this problem!) When we first heard of the issue, it struck us as an ideal application of our favorite image-adjusting tool PhotoGenetics. Reader Jeff Schaefer was kind enough to share a couple of his photos with us, to demonstrate the color bias and the PhotoGenetics "fix" with. (Noted internet personality and megastar "Ryan" also graciously donated his presence.) Click on either image to see a larger view, visit Jeff's page for more examples.)We've always been keen on PhotoGenetics as the "$30 camera upgrade," but even we were surprised by just how trivially it deals with a selective-color problem of this sort. We fiddled around for quite a while in the basic PhotoGenetics program, and ended up with fixes that would work for one photo, but not others. When we tried the "Isocolor" plug-in though, we were frankly amazed by how quickly we got a "genotype" that could be applied to pretty much everything with good results! (The Isocolor plug-in lets you make changes to specific colors in an image, without affecting the image as a whole. It costs an extra $14.95 beyond the base price of PhotoGenetics.) The photos above and below show the results of a PhotoGenetics "genotype" that took us all of about 30 seconds to develop. The best part is that once you have a genotype like this, you can batch-apply it to all your photos in mere seconds. Really phenomenal: In our view, for $45, PhotoGenetics and the Isocolor plug-in turn a great digicam (the S20) into a truly outstanding one! (Frankly, with PhotoGenetics, an easily-corrected color problem like the one shown here should be no reason to bypass anotherwise excellent digicam.)
We review PhotoGenetics elsewhere on this site, but make available here a copy of our S20 isocolor fix for free download. All you should have to do is click on this link, and then tell your browser that you want to save the file to disk. Visit our PhotoGenetics review & click through the link at the bottom to download a free evaluation copy of the program, crop our S20 fix into the "Genotypes" folder, and you're all set to go! If you decide to purchase PhotoGenetics, click-back through the link at the bottom of our review, and you'll get a $5 discount.Reader Comments! --> Visit our discussion forum for the Canon PowerShot S20!
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