The NEX-5 and 3 might well win an award for the lowest number of external controls of any camera. The scarcity of buttons seen on the mock-ups shown at the PMA 2010 exhibition were interpreted by many people to mean the cameras would have a touch screen, but this isn't the case.
In fact, Sony has taken an unconventional approach, and three of the six buttons on the body do not have a fixed function. Instead their functions are context-sensitive - changing in relation to which mode you're in and what you've just done. It's an interesting idea and one that particularly suits the NEX cameras' unintimidating, easy-to-use philosophy.
The effect is initially impressive, particularly in the camera's automated modes. Sony has added the ability to manually configure the actions of the central and lower buttons when shooting in the manually controlled PASM modes, allowing the assignment of up to four key shooting parameters. This, along with the features already offered on the four-way controller, gives a high degree of rapid access to key functions, despite the small button-count.
The Alpha NEX-5 features an all-new, 100% electronic E-mount. Sony has managed to reduce the flange-back distance (the distance from the front of the mount back to the sensor), to an incredible 18mm - 2mm shorter even than the Micro Four Thirds system. This allows the camera to be extremely narrow.
Cleverly, the lens mounts of both the NEX-3 and NEX-5 extend a little way forward from the bodies, making the already thin cameras seem slightly thinner than they are, but even ignoring this optical illusion, it is clear from this diagram that Sony has made impressive size reductions with the NEX-3 and 5 compared to a conventional Alpha DSLR.
To facilitate the shorter flange back distance that is necessary to keep the NEX-3 and NEX-5 as compact as possible, Sony has designed a new lens mount, which it is calling the E mount. Apart from the mechanical locking pin on the bayonet, the E-mount is 100% electronic, and represents a complete break from the semi-mechanical coupling inherited from the old Konica-Minolta Dynax mount used by Sony in its Alpha DSLRs. Losing the physical AF motor and aperture actuator has allowed Sony to reduce the size of both the NEX bodies and their lenses.
Interestingly, one of the consequences of Sony's drive to make the NEX-3 and NEX-5 as small as possible has been to remove the space required for a sensor-based image stabilization system. The NEX-3 and 5 are the first Sony Alpha cameras, in fact, not to feature a variant of Sony's Super SteadyShot stabilization system. Instead stabilization is supplied by Optical SteadyShot units inside some E-mount lenses, including the 18-55mm kit lens, and the forthcoming 18-200mm superzoom.
The NEXs don't feature a built-in flash, but do come supplied with a tiny external unit, which draws its power from the camera's main battery - bolt-in, if you like. The HVL-F7S screws into the camera and plugs into the accessory socket above the lens. Its Guide Number of 7m (at ISO 100) puts it on a par with the built-in units on cameras such as the E-PL1 and GF1, significantly lower than that of the Samsung NX10 and most DSLRs, and a world away from the sort of power you usually expect from an external flash.
It is also worth remembering that with the flash attached, the accessory socket is taken up, and cannot be used for anything else, like (for example) the optical viewfinder for the 16mm pancake, or an external microphone. The NEX cameras are also the only interchangeable lens cameras we can think of that don't offer a hotshoe, so there are currently no options for more powerful flashguns or flash triggers.