Canon Ambassador Audun Rikardsen has mastered the skill of shooting split-level wildlife photographs showing what's above and below the surface of the sea simultaneously. "People think I’m an underwater photographer, but I’d rather call myself a surface photographer. I find it fascinating to see the few thin millimetres that divide these two totally different worlds," he says.

In order to capture these audacious and uniquely creative compositions, Audun has made his own waterproof housings that optimise the camera's ability to focus both above and below the surface in low light conditions. However, he maintains that you can take split-level shots in the daytime with all sorts of underwater housings, as long as you have the correct lens and port – he uses an off-the-shelf offering for some shots, too.

"The wider the lens, the better," he says. "I often use a fisheye lens because the less water you get between your lens and the subject, the sharper and clearer it will be. That's because there are fewer particles in the water to shoot through."

The focal length of the lens also dictates the shape of the port on the front of the housing. Because a lens such as the Canon EF 8-15mm f/4L Fisheye USM offers a 180-degree diagonal angle of view, it's essential to use a dome port. If a flat port is used, part of it will be visible on the edge of the frame.

Settings for sharp underwater shots

"He watched me for many days, so he knew I wasn't dangerous," Audun remembers. "Eventually, he came towards me, lay down nearby and touched my hand with his whiskers. From that moment, we were friends and I could do everything with him. He was very playful and I called him Buddy. As a photographer, this was a once-in-a-lifetime opportunity. I aimed to document this walrus as much as possible and particularly wanted to take a split-level picture."

Photographing Buddy the walrus

Exposing for above and below the water

One of the biggest challenges when shooting split-level images is choosing the correct exposure for above and below the water. Audun has used a range of creative techniques for these images, including double exposures – one for above and one for below the water – and single exposures using flash to light what's below the surface. Audun chose not to use flash for the shot of Buddy, since he wanted to use the sun to naturally light the walrus. However, getting a correct exposure was particularly difficult, because the sun was in the frame and low on the horizon.

"You need a perfect exposure," Audun says, explaining that exposing for the darker conditions underwater would blow out the highlights in the sky, while underexposing the shot would have lost too much detail in the shadows. "I usually expose it a little more than normal to suit the highlight conditions above water, but not so that it burns out." The shot was taken using exposure settings of 1/200 sec at f/13, ISO1000.

Audun says the high dynamic range offered by the Canon EOS 5D Mark III was essential for the image's success because it allowed him the scope to bring out shadow detail underwater at the post-processing stage. "In the original RAW file everything below the surface was quite dark."

Not only is the split-level Buddy shot one of Audun's favourite images, it also won first prize in the Underwater Worlds category of the 2015 Asferico International Nature Photography Competition. "To me this is a relaxing picture because you have the clear sky, the midnight sun and the light reflecting in the bubbles that the walrus is blowing out," he says. "The walrus himself also looks calm. I was lucky to get the sun exactly on the surface.

"In a situation like this, you should never stop taking pictures, even if you think you have the perfect shot. Adjust your settings, change the aperture, alter your position if you see that something could be done better. Don't stop until there's no chance of continuing."