SNELL’S - A WINDOW TO THE SKY
If you want to get an impressive wide-angle photo, there are a few compositional elements you can always rely on. The Snell’s window is one of them, but what is Snell’s window? Mario Vitalini explains Photographs by Mario Vitalini
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nell’s window is an effect caused by light from the sun being refracted when it passes through the waterline and the underwater scene being reflected on the surface. It is named after the Dutch mathematician Willebrord Snellius, who discovered the refraction law we know today as Snell’s window. 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. The darker edges are the reflection of the bottom.
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 15mm fisheye lens on a full-frame or an 8mm on a micro 4/3 (mirrorless) camera will do a perfect job. If you point the camera directly to the surface you will get almost a complete circle, however you can get partial windows by shooting at a lesser angle. The closer to the vertical axis you aim your camera the greater the section of the circle of light you will get.
Exposure considerations
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. 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 to add some texture in the background. You will be shooting upwards and will see the sky, for this reason, I prefer to shoot Snell’s windows when the sky is clear and there are some fluffy clouds.
Diving considerations
When framing your shot bear 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. 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. Is also a good idea to think about your breathing. Shooting upwards will get your bubbles on the frame. Always time your breathing so your bubbles have reached the surface or are out of the picture.
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