Pentax does a good job of keeping noise minimal up to ISO 400, though you can expect to see some grain creep in at ISO 200 when viewing images at 100 per cent on a computer monitor. At ISO 400, noise becomes readily apparent on a computer monitor and starts showing up in prints.
However, Pentax is able to retain a good amount of shadow detail even as the noise begins to grow, which indicates that it's not being overly aggressive with processing to combat the noise. This explains why much of the fine detail seen at lower ISOs sticks around in the middle of the camera's sensitivity range.
By ISO 800, noise takes away much of the finer detail, making text that was readable at lower ISOs unreadable. At ISO 1,600, noise overtakes the camera's images, but the Z10 does a good job of maintaining its colour balance and shadow detail. By ISO 3,200, noise takes over and images become unusable. We'd stay below ISO 800 whenever possible with the Z10 to achieve the best image quality, though you should still be able to get passable prints at ISO 800 as long as they're not very large prints.
Thankfully, one of the as-yet-unsung features of the Z10 is an auto-ISO mode that lets you limit the sensitivity to below whatever ISO you choose from ISO 100 through ISO 6,400. That means that a quick trip to the menu lets you set the camera to select the ISO for you, but stay below ISO 800, which can really help if you don't want the hassle of worrying about settings, but still want decent image quality.
Conclusion
It's not easy for a camera company to make
a small, good-looking camera that takes nice pictures. There always has
to be a tradeoff when you try to cut costs. In this case, Pentax seems
to have traded some time between shots in favour of a long zoom lens and
nice, if not stellar, image quality. As long as you don't mind the
wait, you might be surprised with the images you get from the Optio Z10.
Additional editing by Shannon Doubleday
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