We can tell this from the images, because the shape of the earth changes considerably depending on the location in the frame.

The GoPro HERO4 camera used a fisheye lens. The following screenshots are taken from the video GoPro Awards: On a Rocket Launch to Space.

So if we have an image taken with a fisheye lens and the earth horizon is crossing the center of the frame, the image shows the real curvature of the earth. All lines that cross the center of the frame mostly retain their curvature. Note that the straight brown band that crosses the center of the frame remains straight. This is definitively false as is demonstrated on this page. They claim that fisheye lenses can not straighten or invert curvature, but only exaggerate an already existing curvature. So if the earth horizon is curved convex, like the beck rest in the left image, it will appear flat or even concave (inverted curvature) if the horizon is far enough away from the center of the frame.įlat earther deny that the flat horizon in some images is caused by a fisheye lens. But can a convex curve be inverted to a concave curve by the barrel distortion of a fisheye lens? Yes it can, as the following images show:Ī Fisheye Lens (Barrel Distortion) Inverts the Curvature All straight lines appear curved outwards, except if they cross the center of the frame. If the earth is a sphere and the horizon crosses the center of the frame, the horizon will appear curved and the curvature near the center of the frame is the same as from a non-distorting lens.Ī fisheye lens creates barrel distortion, which bends all objects away from the center. If the earth is flat and the horizon crosses the center of the frame, the horizon will appear flat. We can still get approximately the real shape of the horizon from those images, where the horizon crosses the center of the frame. If in a video the shape of the horizon changes depending on the location in the frame, then a distorting lens was used.If in a video the shape of the horizon shows the same curvature or no curvature no matter where in the frame it is, then the lens is a non-distorting rectilinear lens and shows the real shape of the horizon.If the horizon appears bent when it crosses the center of the frame, using any lens, then the horizon is curved in reality.If the horizon appears flat when it crosses the center of the frame, using any lens, then the horizon is flat in reality.Away from the center the curvature gets more and more distorted, but retains its direction of curvature. Near the center of the frame the curvature is the same as in an undistorted image. That means we can determine the shape of the earth from images that use distorting lenses like fisheye lenses, if the horizon line crosses the center of the frame. Curved lines that cross the center of the frame get distorted as they divert away from the tangent line through the center of the frame, but the direction of the curvature is retained. Straight lines that cross the center of the frame remain always straight. Lines that don't cross the center of the frame are bent by non-rectilinear lenses as shown by the App. If you select Shape = Arc you can change the curvature of the arc with the Size slider. See Distortions in Wikipedia for the equations used. A value of zero does not create any distortion. Positive values for Distortion create Barrel Distortions, while negative values create Pincushion Distortions.

Gopro fisheye lens