Body & Design
To say the Pentax K-01 differs physically from its mirrorless rivals is an understatement. The decision by Pentax to maintain compatibility with its K-mount lenses without the use of an adapter means the camera must accommodate a large flange-back distance (and essentially leave space for a mirror it doesn't have). And Pentax has shown no hesitation in embracing a large-camera aesthetic. Indeed the K-01 is much closer in size to a DSLR than a mirrorless camera.
Build quality appears solid with a sprinkling of aluminium parts adorning the plastic-coated body (there's an aluminium chassis under there somewhere). The front and side plates of the K-01 are covered with a ribbed rubber layer.The rear half of the rubber side-panel doubles as the accessory port door. It makes sense as part of the design but we found slightly awkward to close and have real concerns about its durability, especially as the rubber starts to lose its flexibility over time.
The camera sports a total of 13 external controls points in addition to a 4-way controller. The size of the camera allows for large, easily identifiable buttons, though we have some reservations about the control point layout.
In your hand
With the buttons arranged over such a large camera area, we found key controls difficult to manipulate without large shifts in your hand position. While you can reach both the red and exposure compensation buttons with your hand in the shooting position, neither of them are particularly comfortable, as they are set so far to the rear of the camera plate. The rear thumb dial, by comparison, is very well placed.
There's no getting around the fact, however, that the K-01 is a heavy camera. In addition, it feels particularly unbalanced, with significantly more weight distributed along the grip side of the camera. When using anything other than the Pentax smc DA 40mm F2.8 XS pancake lens, we find the only comfortable option when holding the camera is to support the bulk of its weight with your left hand holding the lens barrel. From an ergonomic handling standpoint, the K-01's external design falls far behind a DSLR form factor like that of the Pentax K-5.
Compared to the Panasonic Lumix DMC-GX1
The Pentax K-01 and the Panasonic GX1 make for an interesting comparison. While both cameras offer 16MP resolution and are available as kits with a very compact lens, the camera bodies themselves sit at opposite ends of the size spectrum for mirrorless cameras.