It seems that the fisheye effect can look different with the same lens. So I want to understand how it works.
For example, I use a Dji Phantom vision 2 drone to take pictures, all of my pictures have been made with the same camera (same lens) and all present a fisheye effect. But it seems that the fisheye effect is different for each picture, does it depend of the distance to the subject (in the case of a drone the subject would be the ground) ?
The fisheye "effect" is dependent only on the angle between the camera and subject, it is thus totally independent of distance.
What you might be noticing is that a fisheye lens bends all straight lines unless they pass through the exact centre of the image.
In some natural scenes the horizon will be the only straight line in the image, thus if you happen to get the horizon dead level then there can be few cues that the image was taken with a fisheye lens. If the next shot has a lower horizon the effect will be very obvious.
Yes, same fisheye lens gives different results depending on distance of the subject, due to parallax error, due to virtual pupil position, but this only happens for very close subjects (probably at distance similar to lens diameter, so probably this does not apply to aerial photos), anywhere see here for reference:
http://michel.thoby.free.fr/Scholtes/Parallaxe/PB_of_Theory_of_NPP.html
http://michel.thoby.free.fr/Scholtes/Parallaxe/Plague%20on%20claustro.html
