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White Balance

The Z850 has fairly comprehensive white balance controls, with six presets (daylight, cloudy, shade, fluorescent N and D, incandescent) and one manual (custom) setting in addition to the default Auto mode. In our tests outdoor white balance was excellent, very difficult to fool. Indoors the results below pretty much reflect our real-world findings; slightly better than average Auto White Balance performance under artificial light (and very good if you use the presets). Like the Z750 before it, the Z850 has a novel feature that allows you to change the white balance setting on a JPEG image after it has been saved. Unlike similar options for RAW files, however, this feature applies a color correction to the saved JPEG, and so can only work with the processed data. The results vary from very impressive (when the white balance of the saved file is only slightly wrong) to almost pointless (it cannot return an orange-tinted incandescent shot to anything approaching normality), but it's a novel feature in a camera loaded with them.

Incandescent - Auto WB
Red 6.2%, Blue -3.3%
Average
Incandescent - Incandescent preset WB
Red 2.2%, Blue 0.6%
Good
Fluorescent - Auto WB
Red 6.1%, Blue -9.7%
Average
Fluorescent - Fluorescent preset WB
Red 1.9%, Blue 0.5%
Good

Flash Performance

After the distinctly lackluster flash performance of the Z750, it would have been unforgivable if Casio hadn't improved things on the new camera, and you'll be pleased to hear they have. Not only is the flash itself much more powerful (now reaching 4.3m / 14 feet) in normal mode. Exposure is generally excellent over the working range (which incidentally goes right down to 10cm / 3.9 inches) and the results are very slightly warm (which is great for skin tones).

There are two new flash modes, Soft Flash and High Power Flash (plus the same 'Flash Assist' option seen on the Z750). Soft flash reduces flash intensity (without altering exposure) and does actually produce slightly less harsh portraits - and is far better for close ups - though in low light it does allow the ISO to rise higher than normal (standard auto flash seems to top out at ISO 200), so you may see a little more noise. High Power Flash mode also increases ISO if your subject is far away (in this mode ISO appears to be allowed to go all the way up to 1600, though I got none at higher than 800). You can also alter the flash output (+/- 1 or 2), and - uniquely - there is a Flash Continuous mode that shoots three flash pictures in rapid succession.

Our only complaint about the flash is that it tends to favor ISO 200 in auto mode, meaning by default flash pictures (which are usually taken at fairly short distances) are noisier than they need to be. Of course you can use manual ISO to avoid this, but you need to be mindful of the fact that doing so will reduce the effective range of the flash unit.

Skin tone ('soft flash' mode)
Slight warm tone, well exposed
Color chart (standard flash mode)
Slightly warm color,very slight underexposure

Macro Focus

The Z850 has a dedicated macro mode that works at all focal lengths, but - as is normal in cameras such as this - is most effective towards the wide end of the zoom. This provides a minimum focus distance of around 10cm giving you an area of just under 9cm across to work with - hardly class-leading but fine for occasional close-up snaps. Inevitably there is some distortion at the wide end of the zoom, but it's not too strong (mainly because compared to many of its competitors, the Z850's macro mode doesn't actually allow you to get very close). There is also a little Chromatic Aberration (CA) visible towards the edges of the frame in macro mode (this is much harder to see in 'normal' shots).

Wide macro - 87 mm x 65 mm
37 px/mm (942 px/in)
Distortion: Average
Corner softness: Average
Equiv. focal length: 38 mm
Tele macro - 124 x 93 coverage
26 px/mm (688 px/in)
Distortion: Average
Corner softness: Average
Equiv. focal length: 114 mm

Barrel and Pincushion Distortion

Whilst there is measurable distortion at the wide end of the zoom (around 1.2%), it is no worse than most compact 3x zooms. It certainly doesn't have a significant impact on real-world shots. There is a small amount (0.4%) of barrel distortion at the long (114mm equiv.) end of the zoom range. Edge sharpness is actually pretty good for a camera in this class.

Barrel distortion - 1.2% at Wide angle
Equiv. focal length: 38 mm
Barrel distortion - 0.4% at Telephoto
Equiv. focal length: 114 mm

Specific Image Quality Issues

Overall the news is good - the Z850 produces clean, detailed results in a wide variety of situations, focus is pretty reliable (failing only occasionally at the long end of the zoom in low light), and white balance very accurate. After complaining strongly about the ridiculously high saturation and sharpening of the EX-Z750's results I was relieved to see that Casio has made some serious changes to the default processing for the EX-Z850. The contrast is now a lot lower (so much so that outdoor images can seem a little flat) and the saturation much more natural, though the sharpening is still a bit high for my tastes. If you prefer a brighter, bolder look 'out of the box' or want flatter results for post-processing, then fear not; the Z850 provides contrast, saturation and sharpness controls (with 5 levels of each available). For printing without processing you might want to turn the contrast (and maybe the saturation) up a notch, but the important thing is that you have the option, and I'd rather have slightly flat images than over-processed images any time.

Now to the niggles; as is unfortunately the norm now there is highlight clipping in bright scenes, and some clipping of very strong reds and magentas, which can produce posterization (though thankfully this is rare except in very bright sunlight), and as mentioned, the default sharpening is a bit too high. I also found a slight, but regular tendency to overexposure when shooting outdoors, which really doesn't help maintain highlight detail - if you find this to be an issue you may want to get into the habit of applying a small negative exposure compensation, especially on bright, hazy days. Although in general we found the exposure system to be fairly robust there were some unusual scenes that foxed it completely, causing gross under or over exposure - though to be fair this is a 1 in a 100 occurrence. Finally there is some purple fringing and a small amount of chromatic aberration (in the corners at full wideangle).

Purple fringing

Noticeable purple fringing is present to some degree in all shots containing very bright (especially overexposed) areas, and in some shots it's very pronounced. It's not enough to mar shots in most circumstances, but wideangle shots on bright days can produce very strong fringes at the boundaries where bright and dark areas meet.

100% crop 38 mm equiv., F2.8

Clipping

By no means a problem unique to the EX-Z850, highlight clipping is made worse by the tendency to overexpose slightly (and can, therefore, be reduced marginally by the careful use of AE-compensation). We also found several examples of channel clipping where the scene contained very bright, bold reds and pinks.

100% crop 114 mm equiv., F5.1

Overexposure

As mentioned above the EX-Z850 tends to slightly over expose - particularly outdoors on bright days. The problem is so consistent that you may well want a -0.3EV exposure compensation permanently set when shooting in bright weather.

38 mm equiv., F2.8 38 mm equiv., F2.8
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