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Color (7.12)
The Casio Exilim EX-Z850 isn’t touted as a really high-performance camera, but consumers still expect it to take good pictures nonetheless. Part of that expectation includes producing realistic colors, as shooters want the grass to be green and the sky to be blue just as they see them. We tested the Z850’s ability to produce accurate colors by photographing the GretagMacbeth industry standard color chart. This chart has 24 colored tiles that are somewhat challenging to reproduce.
We uploaded the Casio Z850’s pictures of that chart into Imatest Imaging Software, which analyzed the data and returned the following modified chart. It shows the original chart in the vertical rectangle of each tile, with the Z850’s version of the color in the outer square of each tile and the inner square showing the luminance-corrected ideal.
Below is another chart that helps us understand how accurate the colors are on this Exilim digital camera. The circles on the chart show the Casio Z850’s colors, and the squares represent the ideal colors from the original GretagMacbeth chart.
Most digital cameras have problems with the red portion of the spectrum; cameras tend to exaggerate these for more flattering skin tones. This isn’t the case with the Casio Exilim EX-Z850 though. This camera has troubles with the blue part of the spectrum. Its overall result yielded a 7.12 overall score with a 9.3 mean color error. There are some definite color balancing issues here, and colors were over-saturated by an average of 14.7 percent.
Still Life Scene
The colorfully saccharine still life scene shown below was captured by the Casio EX-Z850. For a link to the original full resolution file, click on the image.
Resolution (2.57)
The Z850 is marketed with 8 megapixels, but in general Casios haven’t performed well in resolution testing – despite the claims of higher and higher resolution on the image sensors. We used the Z850 to snap several pictures of an industry standard resolution chart. After experimenting with several focal lengths and apertures, we used Imatest to determine that the sharpest results came from an image shot at f/5.1 and 23.7mm (shown below). These are nearly the same settings that the Casio Z1000 had in its sharpest shot: f/5.4 and 23.7mm.
Click on the chart above to view the full resolution image
The camera’s resolution results are expressed in units of line widths per picture height (lw/ph), which explains how many theoretical black and white lines could fit across the frame in both the vertical and horizontal directions without blurring. Looking at the full-resolution file linked above, consumers should be able to see the blurred lines to the right of the frame’s center. The numbers confirm our suspicions. The Casio Z850 resolved 1387 lw/ph horizontally with 9.35 percent under-sharpening and 1438 lw/ph vertically with 10.6 percent under-sharpening.
There was a lot of fluctuation in the amount of in-camera sharpening, or under-sharpening in this case. Under-sharpening in pictures ranged from 9 to 25 percent. The Casio Exilim EX-Z850 does have a sharpening tool in the playback mode, but will be needed to realize the lost resolution.
Noise – Auto ISO (2.64)
The Casio Exilim EX-Z850 isn’t stocked with an accurate metering system, which led to lackluster results in this test. In our brightly lit studio, many digital cameras automatically choose the lowest ISO setting and produce little noise. This model, however, produced the amount of noise found at the manual ISO 200 setting. This unfortunate metering problem brought unfortunate results – an overall score of 2.64.
Noise – Manual ISO (5.79)
The Casio Exilim EX-Z850 has only four manual ISO settings available in full resolution: 50, 100, 200, and 400. We tested the camera’s noise levels at each ISO setting while shooting in optimal lighting. We took the noise garnered at each sensitivity setting and put it into a regression analysis to determine an overall score. The chart below shows the manual ISO settings on the horizontal axis and the noise levels on the vertical axis.
This steady rise in noise looks similar to that of the Casio S600 and Z1000. The Z1000 got by with a 5.7 overall manual ISO noise score, while the Casio Exilim EX-Z850 received a 5.79 score. Noise levels are acceptable at the camera's ISO 50 and 100 setting, but its two higher sensitivities contain more noise than we would have liked to see - particularly with a limited ISO range. This performance isn’t awful, but it certainly isn’t anything to brag about either.
Low Light (2.5)
Most compact digital cameras can take decent pictures in the optimal lighting of a studio, but it is much trickier to shoot good pictures in low light. We tested the Casio Z850 by photographing the color chart under lighting conditions of 60, 30, 15, and 5 lux. The first two tests of 60 and 30 lux are fairly common photography situations found in night clubs, living rooms with shades drawn, and dimly lit restaurants. The last two tests are aimed more for challenging the camera to see where the image sensor’s limits are rather than get a gorgeous picture. Below are the images taken during this test, modified by Imatest Imaging Software to show the ideal colors like the color testing chart.
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Low Light Tests
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60 Lux
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30 Lux
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15 Lux
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5 Lux
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The camera’s auto focus system was an absolute nightmare when shooting the low light tests. Sometimes it worked (like in the 30 lux test) and sometimes it didn’t (like in the 60 lux test). We shot dozens and dozens of photos, and these are the sharpest we could come up with. Other problems occurred while shooting in the low light, color accuracy went out the window, color saturation went below normal levels, and noise crept into the picture and increased the longer the shutter was open.
Below is a chart showing just how much noise infested pictures in the four different tests. The shutter speeds are shown on the horizontal plane and the resultant noise on the vertical plane.
The shutter speeds range from a quarter-second at 60 lux to 2.5 seconds at 5 lux. Noise increased dramatically at 30 lux, when a 1-second exposure was used. It just kept rising from there. In a word, the low light performance of the Casio Z850 is terrible. Colors suffered, the auto focus system was touchy, and pictures are noisy. This Exilim still performed better than the Casio Z1000, but is still a camera users should keep out of the dark and in optimal lighting. If pictures must be taken in less than ideal conditions, set the ISO as low as possible and use the built-in flash.
Speed / Timing
Start-up to First Shot (8.34)
The Casio Z850 isn’t the slowest compact digital camera out there, but it still takes 1.66 seconds to extend its lens and snap its first shot.
Shot to Shot (8.84)
The normal burst mode was not very impressive. It took a picture every 1.14 seconds, which is fast enough to capture a caterpillar crawling across a leaf. Better hope your subjects aren’t any faster.
Shutter to Shot (8.98)
There was very little shutter lag when the camera was pre-focused on a subject. We measured 0.01 seconds between the moment the shutter release button was pressed and the time the picture was actually taken.
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