While Leica's most recent fixed-lens compact camera, the full-frame Q, is a technological marvel, the company hasn't always released compacts that are as polished. The X (Typ 113), released late in 2014, delivered solid image quality for its class when we reviewed it, but was slow to focus and had some operational quirks. Now Leica has taken the same camera and redesigned its body to make it make it waterproof, shockproof, and dustproof, in the form of the X-U (Typ 113). Most underwater cameras feature small sensors that limit image quality, putting the X-U with its SLR-sized image sensor in a class of its own. But it is quite expensive at $2,950, and shares the quirks of the standard X model. Our Editors' Choice underwater camera is still the Olympus Tough TG-4, but you should give the Leica consideration if you're after the more detailed images that a large image sensor delivers—just be prepared to pay for it.

Design
The X-U is about the same size and shape as the X (Typ 113). It measures 3.1 by 5.5 by 3.5 inches (HWD) and weighs 1.4 pounds. Its body is covered in rubber, which not only improves grip—on dry land and under the sea alike—but also helps to cushion it from drops up to four feet. A modest handgrip helps to secure the camera in your hand. The rubber shell and grip make it a bit more comfortable to hold than Nikon's underwater interchangeable lens camera, the 1 AW1. The 1 gives you the flexibility of choosing between a prime or zoom lens, but its 1-inch image sensor isn't the equal of the SLR-sized sensor in the X-U.

View All 6 Photos in Gallery

Top controls include a shutter speed dial, an aperture control dial, and a dedicated button to trigger 1080p video recording. The shutter release is surrounded by the power switch, which is also used to toggle between Single (S) and Continuous (C) shooting. A cold shoe, with a removable protective cover, also sits at the top, centered behind the lens. If you prefer to use an external light rather than the flash that sits at the front of the X-U's lens, you can mount it here.

Buttons run across the rear to the left of the LCD. From top to bottom they are Play, Delete/Focus, White Balance (WB), ISO, and Menu/Set. To the right there's a -/+ control to set exposure compensation when shooting in Shutter or Aperture Priority mode. If you opt for Program mode you'll need to press the EV +/- button before using the -/+ controls. And if you prefer full manual operation the camera switches to Exposure Bracketing mode rather than straight Exposure Compensation—you can use the EV +/- and -/+ controls to set the X-U to capture a series of images at varying exposure settings.

In addition to EV +/-, other controls on the d-pad adjust the flash output (right), activate Underwater mode (down), and set the self-timer (left). Underwater mode, marked as UW, disables in-camera corrections for images. This gives the lens a slightly wider field of view and sets the white balance for underwater use, but also introduces about 2.7 percent barrel distortion (absent from images otherwise). Our test chart showed some serious color fringing at high-contrast areas of the frame that's normally absent when shooting in UW mode, but that won't be as much of an issue when shooting underwater. And if you're photographing a subject up close, depth of field will further hide the blue and yellow chromatic aberration.

The lens is a 23mm f/1.7 prime that delivers roughly the same field of view as a 35mm lens on a full-frame system. It can focus as close as 7.9 inches (0.2-meter). There is a downside to focusing this close—the aperture closes down to f/2.8, cutting the amount of light coming in, in order to maintain acceptable image quality. While I see Leica's point in doing this—the Fujifilm X100T has a similar lens and shows significant image softness when shooting at close range at f/2—it would be a plus for photographers to be given a bit more freedom in choosing the desired aperture, with the understanding that image quality will not be optimal.

That's not the only area in which Leica wrests control. When shooting under bright light, the X-U automatically drops its ISO sensitivity, even if you have it set to a very high level. Again, this is in deference to ensuring that you don't accidentally ruin an image via unintentional overexposure. These type of features are beneficial for getting clearer, properly exposed shots—but should be able to be turned off if desired. 

While I didn't go swimming with the X-U (the downside to reviewing a waterproof camera in New York in late winter), I did take a close look at the design of the physical controls. The shutter and aperture control dials are raised far enough from the body and finished knurled edges that you should have no problem turning them, even when wearing diving gloves. Likewise, the manual focus ring is large, well damped, and a real joy to use—a rarity for a camera with an electronic focus system. Turning the ring automatically brings up a magnified view of the center of the frame so that you can more precisely adjust focus.

The X-U doesn't include built-in Wi-Fi, but will work with an Eyefi Mobi Pro card. There aren't any data connection ports on the body, so you will have to invest in a Wi-Fi memory card or, preferably, an SD/SDHC/SDXC card reader for your computer, to offload images. The memory card and battery are located in the same compartment. It's on the bottom plate and protected by a double-locking door. The battery charger is fairly compact and can plug directly into a wall outlet.

Performance and Image Quality
I ran the same performance tests on the X-U as I did with the X (Typ 113) and results are similar across the board. If you want to do a deep dive into its speed and image quality, you can look at my X (Typ 113) review. But be aware that autofocus is on the slow side—the camera requires about 0.4-second to lock onto a target and capture an image. Burst shooting is available at the same 5fps rate for up to 7 frames at a time.

See How We Test Digital Cameras

In terms of image quality, photos are sharper than what we look for in an image—at its widest aperture the lens scores 1,821 lines per picture height, a solid score for a 16-megapixel camera. That's slightly higher than the 1,747 lines recorded by the X (Typ 113), but sample variation is always at play, and we have changed the lighting in our test studio in the interim between the reviews. Image noise, which detracts from detail as the ISO is increased, scores identically—the X-U keeps noise under 1.5 percent through ISO 1600. And like the X, Raw images tend to be a little bit brighter than JPGs.

Conclusions
The Leica X-U (Typ 113) delivers image quality on par with an SLR in a compact body that can go deep underwater, without the need for an external housing. It stands alone in the market—but it's also priced like a Leica. Though when you consider that a good underwater housing for an SLR or mirrorless camera can cost more than $1,000, the price tag is less shocking. If you want a camera with a big image sensor that you can take on dives, it's worth consideration. But our Editors' Choice recommendation in the rugged compact space stays with the Olympus Tough TG-4. It's a point-and-shoot with a smaller sensor, so its image quality isn't on the same level as the X-U—but its price is a lot more down to earth.