The amount of horizon curvature that appears in a photograph of the horizon depends on several factors:
- The altitude of the observer.
- The field of view of the camera.
- Lens distortions of the camera.
Some flat-Earthers assume that we should see the same amount of Earth’s curvature everywhere. And when they see the different amount of curvature in the different picture of Earth’s curvature, they wrongly took it as “proof” of some sort of misconduct.
If we are to compare the different pictures of Earth’s curvature, we need to take into account all the factors that would result in the different apparent horizon curvature.
- Observer’s altitude: The higher the observer, the higher the amount of the curvature to the observer.
- Camera’s field of view: Lenses with a wider field of view will show more of Earth’s curvature. On the other hand, the narrow field of view of a telephoto lens will reduce the amount of visible curvature.
- Lens distortions: Some lenses —particularly fisheye lenses— distorts lines and will bend or straighten lines in the photograph. We can eliminate or minimize these distortions using defishing software, post-processing software or by placing the horizon line through the center point of the frame.
Photographs of the horizon will appear different if any of the above factors are different. Comparing two different pictures without knowing how the pictures were taken is wrong and pointless.