Canon Powershot S70By: 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 & ConclusionReview First Posted: 9/30/2004
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:
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.
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