The term ultra wides is often reserved for lenses 20mm and wider on a full frame sensor. For a DX sensor, think wider and for a 4/3 system, even more so. The bottom line is the greater the magnification factor of your sensor, the wider the “equivalent” focal length.
Ultra wides are most commonly used in tight quarters to take in the entire space. For instance, if you’re in a small room but you need to photograph all that’s included on the same frame, use an ultra wide. The same holds true if you’re outdoors, in a big city and you need to include the tall buildings in a single capture or in a mountainous area and need to include the peak and its reflection in a lake—an ultra wide may be necessary.
Ultra wides take some getting used to. The wider the lens, the more careful you need to be about not including your feet in the frame. Study every square millimeter of the composition as a very small movement of the camera creates a huge difference in the viewfinder. If you tip the lens up or down, be cognizant of vertical lines that appear along the edges of the frame. The wider the lens, the more they'll distort. The lines bend and may appear as if they'll converge. Some photographers use this distortion as a creative tool. But if the goal is to keep all lines straight, it’s essential to keep the lens perpendicular to the subject.
Another aspect of wide angle distortion about which to be aware is proximity of the closest subject to the front of the lens. The effect can be used to create comic book type effects of people. A huge nose and distorted forehead is the result of photographing a person’s face if placed too close. The effect can be applied to a landscape but to the photographer’s benefit. A small group of flowers can be made to look much larger the closer the lens is placed to it. In effect, the photographer is distorting the reality of the foreground element to create a commanding foreground focal point.
An ultra wide inherently provides an extreme amount of depth of field. Landscape photographers use them in windy conditions as they can use faster shutter speeds to freeze a wind blown foreground. If an ƒ/8 aperture is all that’s needed to provide the depth of field, the corresponding shutter speed may be fast enough to freeze the foreground subject as opposed to the photographer needing to stop down to ƒ/22, which may necessitate too slow a shutter speed. Creatively, ultra wides are great tools. In that they’re not often used, images that show off their positive and artistic qualities stand out in a crowd. They show a fresh perspective. If you have an ultra wide tucked away in your camera bag and don’t often use it, I encourage you to take it for a spin. Re-photograph many of the same subjects in your comfort zone. Get in super close to take advantage of its deep depth of field and exaggerated perspective. You just may find it’s more of a “go to” lens than you thought.
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