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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 12:Test Results & Conclusion

Review First Posted: 9/30/2004

Test Results

In keeping with my standard test policy, the comments given here summarize only my key findings. For a full commentary on each of the test images, see the Canon PowerShot S70's "pictures" page.

As with all Imaging Resource product tests, I encourage you to let your own eyes be the judge of how well the camera performed. Explore the images on the pictures page, to see how the G6's images compare to other cameras you may be considering.

Not sure which camera to buy? Let your eyes be the ultimate judge! Visit our Comparometer(tm) to compare images from the G6 with those from other cameras you may be considering. The proof is in the pictures, so let your own eyes decide which you like best!

The S70 is very similar internally to Canon's PowerShot G6, so a lot of my comments below will match what I had to say about the G6. The main differences between the two cameras are that:

  • The S70's colors are a bit more saturated, particularly in the greens.

  • The S70's image noise, while slightly lower in absolute magnitude, is a little coarser-grained, making it slightly more obvious to the eye, and the S70 also loses a little more subtle subject detail to anti-noise processing.

  • The S70's lens shows more chromatic aberration and softness in the corners of its images than does the G6's, particularly at the wide angle end of its range.

Bottom line though, differences between the G6 and S70 are relatively slight, and both produce very good images. Here's a summary of my findings for the S70:

  • Color: Very good to excellent color. Throughout my testing, the S70 delivered what I've come to call "Canon color," characterized by bright, accurate hues, albeit with a tendency to shift cyans toward blue slightly, which seems to result in better sky colors. Caucasian skin tones were excellent, and white balance was generally quite accurate. As noted elsewhere in this review, the S70's color tends to be a little more "consumer-y" than that of the G6, in that its a little more highly saturated, particularly in the greens. (Foliage colors will look slightly brighter with the S70 than the G6.) The camera's auto white balance option had some difficulty with the household incandescent lighting of my Indoor Portrait shot, but both the incandescent and manual white balance options handled it very nicely. All in all, very nice color. (Click the image at right to see a larger view of the color-error map from Imatest, or see the S70's Imatest page for more complete results and analysis.)

  • Exposure: Good exposure accuracy. The S70's exposure system handled my test lighting well, accurately exposing most shots, and generally requiring about the average amount of exposure compensation on those shots that typically require it. Its default tone curve was a little contrasty, but the low contrast option did a good job of preserving highlight detail under the deliberately difficult lighting of my "Sunlit" Portrait test, although the exposure I had to use to accomplish this left the midtones and Marti's skin tones rather dark. Overall though, a good exposure system with good contrast control.

  • Resolution/Sharpness: Very high resolution, 1,500-1,550 lines of "strong detail." The S70 performed almost identically to the G6 on the "laboratory" resolution test chart. It didn't start showing artifacts in the test patterns until resolutions around 1,200 lines per picture height vertically, but around 1,000 lines horizontally. I found "strong detail" out to at least 1,550 lines horizontally, but only to about 1,500 lines vertically. (And there were strong aliasing artifacts a good 100-150 lines lower than these levels.) "Extinction" of the target patterns didn't occur until about 1,900 lines. Using its "MTF 50" criteria, Imatest reported uncorrected resolution figures of 1305 line widths per picture height in the horizontal direction (corresponding to the vertically-oriented edge), and 1283 along the vertical axis (corresponding to the horizontally-oriented edge), for a combined average of 1294 LW/PH. Correcting to a "standardized" sharpening with a one-pixel radius increased both the horizontal and vertical numbers quite a bit, giving a corrected average of 1573 LW/PH, an excellent result.



  • Image Noise: Good image noise levels, a significant improvement over the G5 model. More importantly, a generally fine-grained noise pattern reduces the impact of the noise somewhat. This chart compares the PowerShot S70's noise performance over a range of ISOs against that of other cameras. The G5 is shown for the sake of historical comparison: It's interesting that both the G6 and S70 have lower noise levels than the G5, even though their CCDs have smaller pixels. A lot of what this chart is showing though, is the difference in anti-noise processing, and some of the most important information doesn't appear here. Namely, the impact that anti-noise processing has on subtle subject detail. The G6 and S70 both use the same CCD chip (and I believe the Sony P150 does as well), so the slightly lower noise levels shown in the chart above for the S70 have to come from more aggressive anti-noise processing. This in fact appears to be the case, as I found that the S70 had a slightly greater tendency to flatten-out subject detail in areas of subtle contrast than did the G6. Likewise the Sony P150, only more so: The P150's noise is indeed noticeably lower in magnitude, but that camera is much more likely to lose subtle detail in hair, foliage, etc. Of the three, I prefer the G6's approach to noise reduction, but the S70 runs a close second.

  • Closeups: A very small macro area with excellent detail, but the flash has trouble up close. The S70 captured a tiny macro area, measuring only 2.26 x 1.69 inches (57 x 43 millimeters). Resolution is very high, and detail were very strong in the dollar bill. Details were softer in the coins and brooch, partly due to the close range and partly to some distortion from the lens that softens detail in the corners of the frame. (Shallow depth of field is an optical fact of life in macro shooting, so isn't the camera's fault. Softness in the corners of images is a consequence of curvature of field in the camera's optics, and is unfortunately a near-universal limitation with digicam macro options.) The S70's flash had trouble throttling down for the macro area, and overexposed the shot. (The camera's lens also blocks part of the flash in the lower right corner.) - Plan on using external lighting for your closest macros shots with the S70.

  • Night Shots: Very good low-light performance, with bright images and good color to the limits of my test. Good focusing with the AF illuminator as well. The S70 produced clear, bright, usable images with good color down to the 1/16 foot-candle (0.67 lux) limit of my test at ISOs 200 and 400, though images were bright to only 1/4 foot-candle (2.7 lux) at ISO 50 and to about 1/8 foot-candle (1.3 lux) at ISO 100. (Average city street lighting at night corresponds to a light level of about 1 foot-candle.) Color balance was pretty good, though pinkish at the lower exposures. Noise was low, at the 50 and 100 ISO settings, creeping upward at ISO 200, and becoming high at ISO 400. Interestingly, while the noise of the S70 is numerically lower than that of the G6, I personally find it a little more annoying. It isn't quite as fine-grained, and the S70 also seems to lose a little more subtle subject detail to its anti-noise processing than the G6 does. The net result is still very good, the S70 did very well in this low-light test. - It's just that it's not quite as good as the G6 here.

  • Viewfinder Accuracy: A tight optical viewfinder, but pretty accurate LCD monitor. The S70's optical viewfinder was a little tight, showing only about 84 percent frame accuracy at wide angle, and only about 80 percent at telephoto. (85 percent is average among digicams I test, but even that amount of tightness is too much, IMHO.) The LCD monitor proved much more accurate, showing 99 percent accuracy at both zoom settings. Given that I like LCD monitors to be as close to 100 percent accuracy as possible, the S70's LCD monitor pretty well hits the mark, but I'd like to see a more accurate optical viewfinder.

  • Optical Distortion: Higher than average barrel distortion, but no pincushion. High chromatic aberration and soft corners at the wide-angle end of the lens' range. Optical distortion on the S70 was higher than average at the wide-angle end, where I measured approximately 1.05 percent barrel distortion. The telephoto end fared much better, as I couldn't find so much as a full pixel of pincushion or barrel distortion. Chromatic aberration was low at medium and telephoto focal lengths, but became quite high at the wide angle end, with as much as 8-9 pixels of fairly strong color visible around the target pattern in the corners. (This distortion is visible as a very slight colored fringe around the objects at the edges of the field of view on the resolution target.) Likewise, the lens also showed a fair bit of softness in the corners of the image, probably about an average amount for a wide-zoom camera, which is to say, a fair bit more than shown by the G6. The S70's lens isn't bad, but it's clear that this is one of the main areas in which the S70 suffers in comparison to the G6.

  • Shutter Lag and Cycle Time: Slightly slow shutter response, good cycle times. With a shutter lag range of 0.93-0.96 second, the S70 is on the slow side of average these days. (The average range is 0.8-1.0 second, still too slow IMHO.) When prefocused by half-pressing and holding down the shutter button prior to the shot itself though, it's very fast, with a delay of only 0.072 second. Cycle times are pretty good, at about 2.2 seconds/shot for the first 10 large/fine frames, and 2.84 seconds/shot for 5 frames in RAW mode. The camera has two continuous shooting modes, managing up to two frames/second for large/fine JPEGs. - See the Timing section of this review for full details.

  • Battery Life: Very good battery life for a fairly compact camera. While I couldn't perform my usual direct power-drain measurements on the S70, I did measure its worst-case run time with a freshly-charged battery at 131 minutes. This is a fair bit better than average for cameras of the S70's size, although I do still strongly recommend purchasing a second battery right along with the S70 when you buy it.

 

Conclusion

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Following the tradition of earlier high-end S-series PowerShots, the S70 is perhaps best described as a "G6 in sheep's clothing." Compared to the G6, about all that's missing are a flash hot shoe, the tilt/swivel LCD, and the G6's internal neutral density filter. Everything else about the camera fits the needs, desires, and interests of "enthusiast" shooters, while at the same time remaining approachable for rank beginners, thanks to a full auto mode and a small assortment of scene modes. In terms of image quality, the S70 is also a near match for the G6. Its color is slightly more saturated, calculated to better appeal to typical consumer tastes, but it gives up a little sharpness in the corners of the frame at the (very) wide angle end of its zoom range, and also has slightly less well-behaved image noise. These are relatively minor quibbles though, as the S70 is an unusually strong performer in virtually every respect. - Another easy choice for a Dave's Pick from Canon...

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