If you want to get a really impressive wide angle shot, there are a few compositional elements you can always rely on. The snell’s window is one one of them.
What is Snell’s Window?
Named after the Dutch mathematician and astronomer Willebrord Snellius who discovered the refraction law that we know today as Snell’s law, the “Window” is an effect caused light from the sun being refracted when passes through the water line and the underwater scene being reflected on the surface.
When underwater, if we look upwards we will see a circle of light with darker sections on the sides. Effectively what our eyes see is a 180 degrees image of the surface, the brighter area, and the reflection of the bottom, the darker edges.
How to achieve a snell’s window
The most important tool you need to achieve a perfect Snell’s window is a fisheye lens. In order to get that circle of light, your lens needs to cover a very large angle of view. a 16mm fisheye lens on a full frame or an 8mm on a micro 4/3 (mirrorless) camera will do a perfect job.
If you want a perfect circle, you will need to point the camera directly to the surface however you can get partial windows by shooting upwards, closer to the vertical axis you aim your camera the bigger the greater the section of the circle of light.
The surface conditions are also important. When there are a lot of waves, most of the sunlight will bounce on the surface limiting the available light underwater, but if the conditions are calm and the seas are flat, the results are great. Technically you want the sea to be as flat as possible however I do prefer when there are a few ripples because these will create beautiful textures in the background.
You will be shooting upwards, therefore, you are going to get the sky in your shot, for this reason, I prefer to shoot Snell’s windows when the sky is clear and there are some fluffy clouds.
Composing for Snell’s window shots
When framing your shot bare in mind you will have to look to the sky, and this creates a series of problems. A well-fitted mask will solve the first one, water in your nose and eyes. By tilting your head up, you will force any water in your mask into your nose and eyes, make sure you clear it properly before you compose.
The other issue you will have to deal with is the fact you are likely to be shutting towards the sun and therefore will need to deal with an incredibly bright background.
To control the risk of overexposure you can use a very high shutter speed and a small aperture but you may end up making the rest of your shot very dark. I do prefer to cover the sun with a subject, it can be a fish, a boat or a diver.
You do not have to point the camera straight up in order to benefit from a Snell’s window in your composition. An angle of at least 45 degrees to the surface will be enough to get a fraction of the circle in your frame.
I particularly like to use the Snell’s window when shooting table corals. If you plan to give this a go, please do pay attention how you position yourself, If you can not get the shot without damaging other corals around.
Once you have tried this, why not try to get your dive buddy to pose next to the coral? The end result can be an interesting play of curves.
When trying to compose shots with multiple subjects you need to be very careful, if you do not position them properly in your frame you may end up with a slightly busy and cluttered shot.
Lighting your Snell’s window picture.
To get a good Snell’s window you will be shooting upwards and that means you will have a huge amount of ambient light getting into your lens. Controlling the exposure is key and the situation normally calls for a fast shutter speed and a small aperture in order to expose for the bright background. If you decide to shoot using only ambient light then you can push the shutter speed to achieve a very sharp silhouette.
If on the other hand, you want to use strobes, you need to pay close attention to the subject distance. Because you will be using a small aperture you will have to crank up the power on your flashguns. If you are too close to your subject you may overexpose it.
Next time you find yourself on a dive with a fisheye lens on your camera have a look at the sky and start practising some Snell’s windows shots, I’m sure you won’t be disappointed.
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