If a distant boat is not visible, then it is because of at least one of these reasons:
- Our eyes have limited angular resolution and are unable to resolve the ship at that distance.
- The atmospheric condition is limiting our visibility.
- The curvature of the Earth obscures the ship.
Flat-Earthers like to demonstrate that a previously invisible ship at a distance can be made visible by zooming in. They would use it to disprove Earth’s curvature. They are wrong. There are reasons other than Earth’s curvature that can obscure a distant boat.
Our eyesight does not have sufficient angular resolution to recognize the distant boat. Zooming in improves angular resolution, and reveals the boat.
It is the same reason germs on our hands are not visible although they are right in front of our eyes. A microscope improves angular resolution and can reveal them.
Zooming in cannot overcome the limited visibility imposed by Earth’s atmosphere, and will never see through the completely opaque barrier in the form of the curvature of the Earth.
If the ship is already behind the curvature of the Earth, then no amount of zoom can make the vessel reappear.
Analysis of the Picture in the Illustration
The top right picture in our illustration is from a YouTube video from a flat-Earth victim.
In the end, the owner of the video told us the maximum amount of zoom is 200×. From Internet search, a popular camera with a 200× zoom is Canon PowerShot SX50 HS. Its base focal length is 24mm (35mm eq). Thus, 200× zoom is 4800mm (35mm eq).
Using the Camera Field of View Calculator, we can find out that at 4800 mm focal length, its horizontal field of view is about 0.43°.
From the picture, we need to estimate what is the length of the ship. Let’s assume the boat is 20 m long. From the shape of the ship, the number looks realistic.
Then, we can now calculate the distance to the ship from the observer using trigonometry: distance = 20m / tan(0.43°) = 2665 m.
Assuming the height of the observer from sea level is 2 m, then the distance to the horizon is 7140 m. It turns out the ship is not farther than the horizon, and cannot be behind the curvature; not even close.