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The build quality is exemplary, with a tough polycarbonate body over an alloy chassis. You'd hardly know it was made of plastic though, and it feels just as solid in the hand as its metal-bodied rivals. It weighs 710g body-only, which is heavier than either the EOS 30D (700g) or the D80 (585g). The body is environmentally sealed against moisture and dust, with weatherproof seals on all body seams, hatches and controls. The camera isn't waterproof as such, but it is splash-resistant. The body design is fairly compact thanks to the low profile of Pentax's pentaprism viewfinder housing, and the large rubberised handgrip is comfortable and ergonomic. The control layout has all the features you'd expect to see on a high-end camera, with a large back-lit LCD display panel on the top plate for shooting data, front and rear command dials for adjusting exposure values, and a large mode dial on the left for the main shooting options. The major control buttons are all sensibly placed for easy operation, and are large and clearly labelled in white on black, which makes the camera easy to operate in low light. One handy feature is the Fn button, which provides a quick menu for adjusting drive mode, ISO, white balance and flash mode. The main menu is both complex and comprehensive, with almost every aspect of the camera's operation customisable to some extent. Thankfully though it is sensibly laid out, with the most commonly used options on the first page, including image size and quality, and adjustments for contrast, saturation and sharpness.
I covered most of the camera's features in my review of the GX-10, but it's worth mentioning a few of the highlights. One that stands out in particular is the viewfinder. Pentax traditionally uses a pentaprism design rather than the penta-mirrors used by some other manufacturers, and the result is one of the largest and brightest viewfinder screens on any comparable DSLR, with approximately 95 percent frame coverage and 0.95x magnification. However it does suffer from a problem that I have found on every one of the several Pentax SLRs that I've owned, and that is a propensity for getting bits of dust in the viewfinder. It's not a serious problem, and the dust doesn't show up on the pictures, but it can be distracting. The K10D has 11 focusing sensor, with nine of them having the faster and more accurate cross-type configuration. These are arranged in a square grid covering the centre portion of the frame, with two additional focus sensors to either side. The positions of the sensors are outlined in the viewfinder by reticule lines.
The other stand-out features are the moving-sensor image stabilisation system and the anti-dust system, which uses a vibrating filter and sticky strip to keep dust away from the sensor. Both of these are very effective, and at the time of the camera's launch were major selling points. However their thunder has been stolen somewhat by Sony and Olympus, both of whom have included similar features on their DSLRs.
The K10D differs from the GX-10 is in two important respects. The Pentax camera has a built-in wireless link for the Pentax AF-540FGZ and AF-360FGZ external flashguns, which allows them to be used remote from the camera body as slave or fill-in flashes with no extra cables. The other difference is the RAW mode. The GX-10 uses the Adobe Digital Negative (DNG) RAW format, while the K10D has the option to DNG or Pentax's own proprietary PEF RAW format. As far as I can tell however there is no particular advantage to either one.