Fisheye Lenses and Lens Distortions

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A photographic lens may have a specific distortion characteristic and strength that may differ from another lens. However, despite the differences, a straight line will always appear straight if it crosses the center of the frame.

Flat-Earthers like to dismiss images taken by a fisheye lens. In reality, the attributes of such a lens are well known. We can use the knowledge to determine if a line in the image is straight, even if it was taken using a fisheye lens.

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Ultra Wide-Angle Lens

An ultra wide-angle lens produces images with an extremely wide angle of view. A lens with a focal length shorter than 24 mm (full-frame equivalent) is considered an ultra wide-angle lens. Ultra wide-angle lenses come in two varieties: rectilinear lens and curvilinear, or fisheye lens.

Because of their wide field of view, Earth’s curvature is easier to observe using an ultra-wide lens. Flat-Earthers incorrectly assumed it means a fisheye lens that distorts straight lines. In reality, there are rectilinear ultra wide-angle lenses that preserve straight lines. With these lenses, if the horizon looks curved, then it must be due to Earth’s curvature itself.

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Defishing Fisheye Images Excessively to Flatten the Curved Horizon

Defishing is a process for removing barrel distortions from fisheye images, producing rectilinear images that preserve straight lines. A different fisheye lens produces a different amount of distortion & needs a different defishing strength.

Flat-Earthers like to apply a stronger defishing parameter than necessary with the goal not to remove the distortions but to make the horizon flat. As a result, they not only remove barrel distortion from the image but also introduce pincushion distortion that straightens the curved horizon.

The horizon in the end image might appear flat. However, it is due to the distortion these flat-Earthers deliberately introduced to the image, not because the horizon is flat.

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Magnitude of Visible Earth’s Curvature in a Photograph

The magnitude of the curvature that appears in a photograph of Earth’s curvature depends on several factors:

  1. The observer’s altitude.
  2. The camera’s field of view or focal length.
  3. The distortion characteristics of the camera lens.

Flat-Earthers like to dismiss a photo of Earth’s curvature by comparing it to another photo showing a different amount of curvature. In reality, to compare the visible curvature, we need to ensure all the images were taken from the same altitude, same field of view, and account for the lens’ distortion.

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Modus Operandi of Flat-Earthers to Obtain “Images of Flat Earth” to Deceive Us

If Earth is a sphere, how is it possible for flat-Earthers to show us “images of flat Earth” taken from high-altitude balloons? These are the modus operandi of unscrupulous flat-Earthers to obtain such images in an attempt to deceive us.

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Why Fisheye Lenses Are Used

Cameras with a fisheye lens are used in the ISS, high-altitude balloons, rocket bodies, and other purposes. The reason is that fisheye lenses have several advantages over rectilinear lenses.

Flat-Earthers claim there is an evil intention behind the usage of fisheye lenses. In reality, the use of fisheye lenses is not unreasonable. If it is desired to have a rectilinear image output, then it is not hard to defish fisheye images to rectilinear ones..

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Fisheye Videos

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In images taken using a fisheye lens, a straight line will remain straight if it crosses the center of the image. We can use this attribute to determine if a line is straight in reality.

In any fisheye videos taken from a high altitude, there should be plenty of moments where the horizon crosses the center of the image, and we can use those to determine that the horizon line is curved in the real world.

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Proofs of Spherical Earth Presented by Flat-Earthers

Many adherents of flat Earth have spent a lot of effort and money to perform various observations and experiments. They would buy expensive equipment, travel to the other side of the world, painstakingly designed the experiments in minute details, and performed large-scale experiments; all to prove the notion that Earth is flat. However, many of these experiments and observations have actually confirmed the Earth is a sphere beyond any doubt.

In most cases, they would not accept such conclusions, and instead, they misinterpret, refuse to accept, lie, and withhold information. Such behaviors are the results of confirmation bias. However, their results speak louder than their biased conclusions, and these are perfectly valid proofs that Earth is a sphere.

These are some of those observations and experiments, where flat-Earthers have painstakingly and extravagantly performed them, only to come up with the wrong conclusions and spectacularly demonstrating their confirmation biases to the entire world.

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Fisheye Lenses Can Make Curved Lines Appear Flat

A fisheye lens distorts images. It results in images having barrel distortions. In a fisheye lens, a straight line can appear curved. But some flat-Earthers don’t realize that the opposite is also true, a fisheye lens can easily make a curved line look straight.

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Curvature of the Horizon in High-Altitude Balloon Footage

High-altitude balloon footage is often abused by flat-Earthers to show us that the Earth is flat when seen from a high altitude.

We analyzed more than two dozens of footage taken from high-altitude balloons on YouTube, and we can easily conclude the curvature is there and usually easy to spot, including in the cases where flat-Earthers use the video as ‘proof’ of a flat Earth.

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