IF I ASKED whether you’d ever taken an underwater photo that was impossible to see at the time, you’d think I was crazy. But if you have ever tried split-level photography, then you can answer that question: yes!
It isn’t something we think about often, but the only way you can see a split-level image is through an underwater camera.
Half-and-half images are among the most compelling underwater photographs because, in addition to showing the impossible, they also transport viewers under water.
They wow land-loving audiences because they show them the world with which they are familiar and introduce them to ours all in one image.
They say that a photo is worth 1000 words. Split-level photos must be worth 2000.
Taking a split-level is not difficult – the challenge is producing a good one. We need the right equipment, the right conditions, the right technique and, the most often overlooked, the right subject matter.
The equipment is relatively simple. We need our widest lens and our biggest dome-port. The wider the lens, the more above and below we can show compared with the meniscus line at the surface.
If you don’t own a really wide lens, shoot in a vertical format to give yourself the widest-possible view.
A large dome-port helps on two fronts. First, it makes it much easier to control the surface of the water.
In a swimming pool, lake or on an extremely calm day, we can shoot splits with small domes (4-5in), but in more normal conditions larger domes (6-9in) make everything much easier.
Second, the larger the dome port, the easier it is to get both the above and below halves in focus.
Understanding why means grappling with dome-port optical theory, so simply remember that size matters!

CONDITIONS ARE CRITICAL to success. A successful split requires reasonably calm water, to allow us to manage the surface on the dome.
The classic prime time to shoot split levels is when the sun is out and high in the sky. High sun ensures the maximum light penetration into the water, and the most even exposure above and below the surface.
Sunshine also means that we can shoot without strobes, which makes the process much simpler and the housing easier to manoeuvre at the surface.
A low sun can be used for more dramatic lighting, incorporating silhouetted scenes above the water
and/or beautiful sunsets, and calls for the use of flash to light up the underwater section.
In very shallow water, such as in rivers, we may want to position our strobes out of the water, but aimed down. In more typical conditions, we can just position them under water.
Some photographers swear on using 45° viewfinders for splits, but for me it really depends on the situation.
If we are standing in the pool or lying half out of the water in a shallow river, then an angled viewfinder is ideal.
If we are swimming in deep water, a straight viewfinder is preferable.
Of course, few of us own both types of viewfinder (I don’t) and even fewer would go to the effort of changing over for a specific shot.
However, I always remove the rubber viewfinder eye-cup on my 45° viewfinder when shooting splits, to stop this retaining water that will obstruct the viewfinder when I lift the camera out of the water to shoot.
JUST LIKE ANY OTHER TYPE OF PHOTO the essentials of focus, exposure and composition remain. In general we should always focus on the underwater part of a split level, and rely on depth of field to keep the above-water section sharp. I’ll come onto why in a moment.
We can either use an off-centre focus point (in the lower half of the frame) to achieve this, or focus on the underwater subject and then lock the focus.
Locking the focus is preferable in rough conditions, when the movement of water up and down the dome will certainly confuse any autofocus.
To understand the reason why we must focus on the underwater section of the image, we need to consider how a dome-port works in water.
In air a dome has no optical effect on your lens, but under water it acts as a negative lens. This means that under water the camera has to focus much closer than the true distance of the subject.
If we take a split of a buddy standing waist-deep in a swimming-pool through a dome-port, his legs will require a much closer focus than his chest. To get both in focus, we need lots of depth of field.
With any lens, depth of field extends twice as far behind the subject as in front. So for an under-over image we must focus on the closer (in terms of focus) underwater subject, and use depth of field to keep the more distant above-water section sharp.
If we focus above the water, the underwater scene will usually be blurred.
And even when we correctly focus on the below-water section, we must still stop down the aperture to secure as much depth of field as possible.
Exposure is usually a compromise. Even in ideal conditions the above-water part will be brighter than the underwater part, so we need to find an exposure that works for both.
I tend to aim to slightly over-expose the above-water half, knowing that I can pull it back in post-processing and can also brighten up the underwater part.

THE FINAL INGREDIENT for success is a winning composition, and for a split-level image this means that there must be a visual reason for the split – subject matter or a narrative that requires an image of two halves.
Great split-level images have good-quality subject matter above and below the surface.
Just as an example, in the Red Sea, where you won’t find palm trees or fluffy clouds, most splits taken in the middle of the day are empty in the top half.
In this destination we’re best shooting splits at sunset, when the sky is transformed from monotonous blue to attractive hues.
Split levels are among the most eye- catching underwater images, but creating winning shots relies on us catching perfect conditions, identifying compelling subject matter and executing our technique precisely.

Wide-angle accessory wet lenses that fit on the front of compact camera systems are not suited to split-level shooting. Their problem is that they get a split at both ends.
We need to keep the space between the lens and camera either wet or dry. Some photographers seal up the join with electrical tape to keep the water in or out.

Droplets on our dome can ruin a shot. Everyone has their favourite cure: licking the dome, dipping it just before shooting and so on.
The best solution is never to get the dome wet in the first place. Impossible if we try to shoot splits at the end of a dive, but easy if we get in the water specifically to make this type of image.

Split levels look best with as many layers at possible. We can actually increase the interest in the image by including the attractive reflection and refraction patterns on the surface (or underside of the surface).
If the underwater subject is a bit deep to fill the frame, lift the camera slightly and fill the empty space with more surface.