Compared with the Nikon D7100

To give some impression how big (or, rather, small) the E-M1 is, we've put it side-by-side with some of its peers - its little brother, the E-M5 and the kind of high-end camera it'll have to face up to: the Nikon D7100.

Though the Nikon D7100 is relatively small by SLR standards, it looks quite large next to the OM-D E-M1. Note that both cameras have two function buttons on the front, and dual front and rear control dials.
From the top, the overall package is also noticeably smaller. Despite its smaller surface area, the E-M1 can host more controls on top thanks to its lack of a top-deck status LCD. While not quite as full and deep as the D7100's grip, the E-M1's will fill most hands.

Compared with the Olympus OM-D E-M5

Noticeably more substantial compared to the E-M5, the E-M1 is a little taller and wider. Whereas Olympus was trying to keep the E-M5's front surface clean to evoke the simplicity of the film OM cameras, the E-M1 is clearly working to appeal to more advanced enthusiasts.
From the top, the E-M5's body looks positively slim by comparison. A larger rear rubber guard surrounds the electronic viewfinder on the E-M1, apropos to its larger magnification. The shutter button's position out on the leading edge of the grip will also feel more familiar to enthusiast shooters. This feature costs more for E-M5 users, who have to purchase the $300 accessory grip which duplicates the shutter button and front control dial.

Body elements

The E-M1 offers similar options to the E-M5 on its mode dial, but gains the Photo Story feature we saw on the E-P5.

Any of the positions on the mode dial can be over-written with a user-defined 'Myset' preset, if you would like quick access to your preferred settings.

Finally, note the locking toggle in the center, which gives the option to either lock the mode dial or leave it free-spinning.
A raised button emplacement on the top left of the camera includes two buttons, each of which presents two parameters in the viewfinder when pressed.

Pressing the AF/Metering button presents focus mode options at the bottom of the screen and metering modes at the top - spinning the rear dial changes AF mode, while the front one sets metering. The other button gives control over drive mode and High Dynamic Range shooting.

There is also the option to have these buttons' functions change, when you flip the 2x2 switch on the right of the viewfinder.
The E-M1 includes two customizable buttons on its front plate - one has an indentation to allow you to distinguish between them by touch.

By default, the upper button is set to measure a custom white balance, while the lower is for depth of field preview. This sets the lens to the taking aperture to give show what will and won't be in focus in the final image.
The E-M1 becomes the first Olympus Micro Four Thirds camera to have a built-in microphone socket, so there's no need to use the SEMA-1 accessory mic port.

Just below the Mic socket are the micro-HDMI and AV/USB connectors, concealed beneath a hinged rubber door. The lower of these two is also compatible with Olympus's RM-UC1 wired remote release (or third party clones).

Note that the E-M1 has no infrared wireless release. However it can be controlled by a smartphone or tablet over Wi-Fi using Olympus's OI.Share app.

The card slot on the E-M1 gets its own door, rather than being bundled in with the battery. This is always nice to see, since it makes it easy to access the card when the camera's on a tripod.

One slightly disappointing omission at this price point is dual card slots, but this is dictated by the E-M1's relatively slimline body.
The E-M1 has an AP2 accessory port, making it compatible with the full range of add-on units created for the PEN and OM-D line - including Macro Light and PEN Pal Bluetooth modules.

It usually sits behind a small rubber weatherproof cover, that itself is held in place by the hot-show cover.
The AP2 port is also required to mount the FL-LM2 flash bundled with the E-M1.

This little flash unit isn't particularly powerful in its own right, but can be used to trigger and wirelessly control Olympus's range of wireless flashguns.
Another give-away that Olympus sees the E-M1 as its most pro-orientated model is the flash sync socket on the camera's front.
The E-M1 uses the same BLN-1 battery that is used by the E-M5 and E-P5. It's a 9.2Wh unit, that is good for around 350 shots (according the CIPA standard testing).

For such a high-end camera, this number is a little low - we're a bit surprised that Olympus hasn't used the additional space created by the larger grip to provide a larger battery.
On the base of the camera is an expansion connector that allows its use with the HLD-7 accessory grip.

The grip duplicates much of the camera's controls, as well as incorporating an additional battery. It also has buttons that can be customized independently of the ones on the camera body.

HLD-7 Vertical Grip

This is the E-M1's HLD-7 vertical grip. It has a compartment for a second battery, and replicates the dual control dials as well as the shutter button. It also has two customisable 'B-Fn' buttons, which can be set to either replicate the camera's main Fn buttons, or do something else entirely - it's your choice. There's also a little slot for storing the camera's connector cover.

You can't easily reach the camera's four-way controller when using the vertical grip, but you can configure one of the B-Fn buttons to activate AF point selection, then move the focus point around the frame using the front and rear dials.

As well as providing a set of controls for portrait format shooting, the HLD-7 provides extra grip area when holding the camera in landscape format. This makes for a more comfortable experience with larger lenses.

We suspect the grip will be de rigueur for photographers using Four Thirds lenses, especially sizeable ones like the Zuiko Digital ED 50-200mm 1:2.8-4 SWD.
The HLD-7 has a slot for an additional BLN-1 battery, to double the camera's stamina. There's also an input for a mains power source.

This being Olympus, you can decide which battery you want the camera to use first - the one in the vertical grip, or the one in the camera itself.