Digital
Cameras - Olympus C-720 Ultra Zoom Test Images
(Original test posting: 7/1/02)
I've begun including links in our reviews to a Thumber-generated
index page for our test shots. The Thumber data includes a host of
information on the images, including shutter speed, ISO setting, compression
setting, etc. Rather than clutter the page below with *all* that detail,
I'm posting the Thumber index so only those interested in the information
need wade through it!
Good color overall, but high contrast and somewhat dark midtones.
The extreme tonal range of this image makes it a tough shot for many
digicams, which is precisely why I set it up this way. The object is to
hold highlight and shadow detail without producing a "flat"
picture with muddy colors The C-720 did fairly well, but had rather high
contrast. Adjusting the contrast to the "low" setting helped
quite a bit, keeping highlights in check while increasing midtone detail,
but I'd still like to have seen brighter midtones at exposure levels that
kept the highlights in check. (See the contrast series below.) The
shot at right was taken with a +0.3 EV exposure compensation adjustment,
which still produces slightly dark midtones (a shot at +0.7 EV seemed
way too bright). I chose the Auto white balance
setting as the most accurate, though the Daylight
setting produced nearly identical results. Skin tones look pretty good,
but the blue flowers have a bit of a purplish tinge (a common problem
with this shot). Resolution is high, with strong detail in the flower
bouquet as well as in Marti's features, though details look a little soft.
Shadow detail is also good, with moderate image noise.
To view the entire exposure series from zero to +0.7 EV, see files C72OUTLCAP0.HTM
through C72OUTLCAP2.HTM on the thumbnail index page.
Higher
resolution, though again slightly dark midtones and high contrast.
Overall results are similar to the wider shot above, and the C-720's
long zoom lens helps prevent distortion of Marti's features. The camera's
high contrast again gives it a hard time coping with the harsh lighting
here, even with its contrast option set to "low." Resolution
is much higher here, with great detail in Marti's face and hair. Details
are much sharper in this shot, with better definition than in the wider
portrait above. Shadow detail is moderate, with low noise. The main shot
was taken with a -0.3 EV exposure compensation adjustment. Here's a sample
image at the +0.0 EV exposure setting, which
is a touch too bright.
Plenty of flash power and even illumination, but
a lot of exposure boost needed. Also a slight orange cast from the room
lighting.
With the help of a +1.7 EV exposure compensation
adjustment, the C-720's flash illuminated the subject well, with good
intensity. The default exposure setting badly
underexposed the shot, with weak flash intensity and slight bluish tints
in the shadows of the Marti's shirt. There's also an orange color cast
from the strong incandescent lighting in the room, which dissipated slightly
with the brighter exposure. Color on Marti and the flower bouquet looks
pretty good, though some orange tints appear in the shadows on her face
and in her hair. I also shot with the Slow-Sync
flash mode, which resulted in more even lighting from the longer exposure.
However, flash power was again low, and the overall exposure very dim
with a yellow cast.
This shot is always a very tough test of a camera's white balance capability,
given the strong, yellowish color cast of the household incandescent bulbs
used for the lighting. The C-720 performed fairly well here, though both
the Auto and Incandescent
white balance settings produced warm casts. The Auto setting resulted
in the warmest image, so I chose the Incandescent setting as the most
accurate. I chose an exposure adjustment of +1.0
EV, but found the results rather contrasty. The C-720's Low
Contrast setting corrected this problem, but increased the yellow
cast slightly. Skin tones are warm from the color cast, and the blue flowers
are dark and purplish (a common problem among digicams with this shot).
To view the entire exposure series from zero to +1.3 EV, see files C72INTP0.HTM
through C72INTP4.HTM on the thumbnail index page.
ISO Series:
The C720 has an option for variable ISO, so I shot the series below at
each of the three ISO options. Image noise on the C720 is a little odd.
It shows the most noise in the blue channel, which is typical for digicams.
What's strange though, is that the green channel shows the next most noise,
quite a bit more than appears in the red channel. - Usually the green
channel is the most noise-free. Overall noise seems a bit higher than
average at the ISO 100 setting, increases at ISO 200, and becomes quite
pronounced at ISO 400. Increased ISO always brings more noise with it,
but the C720 seems to start off with a bit more than usual.
A very slight color cast, but great detail and resolution.
Both the Auto and Daylight
white balance settings produced good results on this shot, although, the
Daylight setting was just a little warm. The Auto setting also has a slight
yellowish cast, but overall color is still good. Resolution is high, and
detail is strong in the tree limbs above the roof and in the shrubbery
in front of the house. Details are also fairly sharp throughout the frame,
though the corners are slightly soft. The fine foliage details in front
of the house are very well-defined, apparently helped along somewhat by
the in-camera sharpening and the camera's inherently higher contrast.
This image is shot at infinity to test far-field lens performance. NOTE
that this image cannot be directly compared to the other "house"
shot, which is a poster, shot in the studio. The rendering of detail in
the poster will be very different than in this shot, and color values
(and even the presence or absence of leaves on the trees!) will vary in
this subject as the seasons progress. In general though, you can evaluate
detail in the bricks, shingles and window detail, and in the tree branches
against the sky. Compression artifacts are most likely to show in the
trim along the edge of the roof, in the bricks, or in the relatively "flat"
areas in the windows.
This is my ultimate "resolution shot," given the infinite range
of detail in a natural scene like this, and the C-720 does an excellent
job here. The leaf and branch details in the tree limbs above the roof
are very well defined, even those that are at a fair distance behind the
house. The shrubbery and fine foliage in front of the house also have
great detail, with very good definition. There's just the slightest hint
of corner softness on both sides, but the rest of the frame is sharp.
The camera picks up a lot of detail in the bright white paint around the
bay window, though it loses some of the more subtle details. The shadow
area above the front door shows strong detail in both the brick pattern
and porch light. The Auto white balance setting produces good color, though
the greens are a bit yellowish. Overall, a very good performance. The
table below shows a our standard resolution and quality series, followed
by ISO, Contrast, and Sharpness series.
I routinely shoot this series of images to show the field of view for
each camera, with the lens at full wide angle, at maximum telephoto (8x,
in this case), and at full telephoto with the digital zoom enabled. The
C-720's lens is equivalent to a 40-320mm zoom on a 35mm camera, really
reaching out there for distant details. Following are the results at each
zoom setting.
This shot is frequently a tough test for digicams, as the abundance of
blue in the composition usually tricks white balance systems into producing
a warm color balance. As it happens though, the C720 went a bit the other
way, producing a pale, slightly bluish image with the Auto
white balance setting. Alternatively, the Daylight
white balance produced a warmer tones, with a bit of a reddish tint in
the blue background. Despite the red tint in the background, skin tones
look more natural with the Daylight white balance. The blue robe came
out a bit greenish from the warm cast, but still nearly accurate. Only
faint purple tints exist in the robe's deep shadows, a common problem
with this shot as this blue is difficult for many digicams to interpret.
The embroidery of the blue robe has strong, well-defined details, and
resolution appears high throughout the frame.
About average macro performance, but good resolution and detail.
The C-720 performed about average in the macro category, capturing a
slightly large minimum area of 3.93 x 2.95 inches (100 x 75 millimeters).
Resolution is very high, with sharp, well-defined details in the dollar
bill, coins, and brooch. Exposure is just a little bright, and overall
color with the Auto white balance is a little warm. The wide-angle lens
position also results in quite a bit of barrel distortion. (There's also
a little corner softness.) The C-720's flash
had trouble throttling down for the macro area, overexposing the shot.
The long lens also casts a shadow from the flashes light in the lower
left corner.
Both the Auto and Daylight
white balance settings produced slightly warm images, though the Daylight
setting had the stronger cast. Exposure looks good, although contrast
is a little high (noticeable by the small loss of detail in the shadows
and highlights). That said, the C-720 picks up the subtle tonal variations
of the Q60 target well, up to the "B" range. Color saturation
is pretty good, as is color accuracy apart from the slight warm cast.
The deep shadows seem to be where the C720 had the hardest time, as the
shadow area of the charcoal briquettes shows only weak detail, with a
moderate noise level. (The noise "grain pattern" is also rather
large, making it more evident than might otherwise be the case.)
Low-Light Tests
Good exposures at light levels well below typical city street lighting.
With full manual exposure control and a maximum shutter time of eight
seconds, the C-720 does pretty well in the low-light category. At ISO
100, the camera captured bright, clear images at light levels as low as
1/4 foot-candle (2.7 lux), though the target remained visible as low as
1/16 foot-candle (0.67 lux). At ISO 200, images were usable as low as1/8
foot-candle (1.3 lux), and as low as 1/16 foot-candle at ISO 400. The
camera's Noise Reduction system did a fairly good job of eliminating image
noise, however, a few bright pixels of noise made it into all of the images
(with the highest level at ISO 400). Typical city street lighting equates
to about one foot-candle (11 lux), so the C-720 ought to do a good job
with much darker shots. The Auto white balance setting produced good color,
though was slightly warm at the dimmer exposures. The table below shows
the best exposure we were able to obtain for each of a range of illumination
levels, at each ISO setting. Images in this table (like all of our sample
photos) are untouched, exactly as they came from the camera.
1fc
11lux
1/2fc
5.5lux
1/4fc
2.7lux
1/8fc
1.31lux
1/16fc
0.67lux
ISO
100
2 secs
F2.8
5 secs
F2.8
8 secs
F2.8
8 secs
F2.8
8 secs
F2.8
ISO
200
1.3 secs
F2.8
2.5 secs
F2.8
6 secs
F2.8
8 secs
F2.8
8 secs
F2.8
ISO
400
1/ 2 secs
F2.8
1.3 secs
F2.8
3 secs
F2.8
5 secs
F2.8
8 secs
F2.8
Flash Range Test
Good intensity all the way to 14 feet.
The C-720's flash remained bright all the way to 14 feet from the test
target, though it decreased in intensity slightly at the greater distances.
Flash power was brightest from eight to 10 feet, and decreased incrementally
from there, so I'd rate it as having a range of about 10 feet. Below is
our flash range series, with distances from eight to 14 feet from the
target.
Great
performance, with strong detail to 1,000 lines/picture height.
The C-720 performed well on the "laboratory" resolution test
chart. It started showing artifacts in the test patterns at resolutions
as low as 600 lines per picture height, but I found "strong detail"
out to at least 1,000 lines. "Extinction"
of the target patterns occurred at about 1,300 lines.
Optical distortion on the C-720 is lower than average
at the wide-angle end, where I measured a 0.54 percent barrel distortion.
The telephoto end fared much better, as I could only find about one pixel
of barrel distortion. This is a surprisingly good performance for such
a long-ratio zoom lens. Chromatic aberration is moderate, showing fairly
light coloration on either side of the target lines in the corners. (This
distortion is visible as a slight colored fringe around the objects at
the edges of the field of view on the resolution target.) There's quite
a bit of blurring in the extreme corners though, particularly at the telephoto
zoom setting. Fortunately, this softness doesn't extend very far into
the image area.
The C-720's electronic viewfinder (EVF) is very accurate at both wide
angle and telephoto lens settings. At wide angle, I measured an approximate
99 percent frame accuracy. At telephoto, the viewfinder was very slightly
loose, but very close to 100 percent frame accuracy. (Frankly, the coverage
was probably exactly 100% for both zoom settings, the minor differences
reflecting the margin of error in my measurements.) Given that I generally
prefer LCD monitors to be as close to 100 percent accuracy as possible,
the C-720 does an excellent job here. Flash illumination at wide angle
is bright and even, with only slight falloff at the corners and edges
of the frame. At telephoto, flash distribution is also very even.
