Dwayne Kellum’s video “High Altitude Balloon 24 (I_See_Stars!)” shows the curve of the horizon. This is visible when the horizon is both above and below the center of the frame.
The camera is a Sony A7s II. The Lens is a Sony FE 50mm F1.8.
This lens is very rectilinear. Here is the quantification of the rectilinear properties:
This grid shows the non-fish nature of this lens. A fish-eye lens or one with strong barrel distortion causes straight lines to curve. This lens does not have such a problem. It does not matter if a line is above or below the center of frame. There is not induced curve from the lens.
Here is a screenshot from Dwayne’s video at 117,431 feet, the yellow line is added to see the curve:
Here is the same screenshot compressed to 10%:
At launch the height is 121 feet, the pressure is 29.88 inHg. https://youtu.be/JkrIm0ZUyJY?t=81
121 feet = 0.022917 miles = 36,881 meters = 36.881 km
29.88 = 758.95211 torr = 101,185 Pascals
At apex the height is 121,196 feet, the pressure is 0.15 inHg. https://youtu.be/JkrIm0ZUyJY?t=8058
121,196 feet = 22.95 miles = 36,941 meters = 36.941 km
0.15inHg = 3.81 torr = 507.9583 Pascals
MCToon 