...I didn't realise you could see curvature from normal commercial aircraft...
Sort of. With all the lack of rigour of any "back of a fag packet" calculation, assume a horizon 180 miles away with an aircraft
6 miles up (rough and ready but the order of magnitude is about right). As you are looking down on a horizon which is a circle
of radius 180 then, at 30° from the direction the camera is pointing in, if you drop a perpendicular from the horizon at that
30° offset to the line of sight of the camera then the intersection is about 160 miles away (180*cos(30)). Draw a straight line
from the horizon 180 miles away to both the aircraft 6 miles up and the ground immediately below it. The angle subtended
has a tangent of 6/180 which is about 1.909°. Similarly, the angle subtended from a point 160 miles away is about
2.148°. This is a difference of about ¼°, which is about half the angular diameter of the Sun or Moon.
The effect in your shot looks to be about equivalent to the full angular diameter of the Sun. If your lens can see to 40°
either side of central then a full angular diameter is about right and I've made myself unpopular because nobody likes a
So, what was the field of view of your lens? Any less than 40° and we might have to blame a little of the effect on
either optically bad window glass or my rubbish calculation.