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Photographers often notice that objects near the edges of wide-angle images look stretched or distorted. A round object can look like an ellipse, and people standing near the sides of the frame can appear unnaturally wide. This effect is usually blamed on the lens, as if wide-angle optics inherently distort the world.

What’s actually happening is more interesting.

Rectilinear lenses don’t distort shapes on a flat frontoparallel (parallel to the camera’s sensor plane* and *perpendicular to the optical axis) plane

A rectilinear lens (the standard perspective projection used by most photographic lenses) has one key geometric property:

Straight lines in the world project to straight lines in the image.

The projection maps a 3D world point (X, Y, Z) to image coordinates

x = f * X / Z

y = f * Y / Z

If the scene consists of a flat plane perpendicular to the optical axis, then every point on that plane has the same depth Z = Z0. The projection becomes a uniform scaling of the coordinates:

x = (f / Z0) * X

y = (f / Z0) * Y

A uniform scale preserves shapes. A circle stays a circle. A square stays a square. Angles stay angles. Even if the field of view is extremely wide, an ideal rectilinear lens will not turn circles into ellipses on a frontoparallel plane.

Where does the wide-angle look come from? The stretching comes from the scene, not the lens. Wide-angle lenses capture a larger portion of the world, and the parts near the edges of the frame are usually not on a frontoparallel plane. In everyday scenes, surfaces toward the edges are viewed from a more oblique angle, and from a different distance than surfaces at the center.

These two effects — tilt and distance variation — are what produce the characteristic stretching.

1. Surfaces at the edges are typically tilted relative to the camera. If you look straight at a circle on a wall, you see a circle. If you look at the same circle from the side, it becomes an ellipse. The same thing happens in wide-angle photos. The lens is still facing straight ahead, but the scene near the corners is not. A person standing near the edge of the frame is turned partly sideways relative to the camera’s viewpoint. A circle painted on a floor or ceiling is seen from an angle. Those tilted surfaces naturally produce elliptical projections.
2. Objects near the edges are often physically closer to the camera. Perspective magnification is proportional to 1 / Z. If an object is closer to the camera, it is magnified more strongly. Wide-angle lenses often place you physically close to your subjects, so the parts of the scene at the edges of the frame are not only tilted — they are also closer than the central region. That combination makes them appear stretched.

The stretching is the world, faithfully projected. A rectilinear wide-angle lens is not distorting the world. It is revealing a wider slice of it, including surfaces that face the camera at oblique angles, are at different distances, and occupy a larger angular extent in the field of view. The edges look stretched because the scene itself looks stretched from that vantage point. The lens is simply obeying the geometry of perspective.

The wide-angle look is not a flaw of the lens. It is a geometric consequence of perspective when you capture a large field of view from a fixed position. Objects at the edges of the frame are usually closer to the camera and oriented at an angle, and an ideal rectilinear projection faithfully records those facts. That is why real scenes photographed with wide-angle lenses show stretching at the edges, even though a perfectly frontoparallel test chart would not.