I have a ball captured in an image. The ball is detected as circle when it is at the center of the image. when it moves to the corner of the image it is detected as an ellipse. We use a fish eye/wide angle lens and we are not correcting the image. We do the circle and ellipse detection on the original image. I want to know if this is a phenomenon of perspective distortion or due to the fish eye/lens distortion ? or anything else.
I did some reading around it and things are confusing me. https://books.google.com.sg/books?id=SFgfgFrdB_oC&pg=PA35&lpg=PA35&dq=sphere+becomes+eliptic+camera&source=bl&ots=dRUkJecnyW&sig=YItExPSKQOGa0TkNRFO332Mh-iU&hl=en&sa=X&ved=0ahUKEwjsluWRwODYAhWMwI8KHXZeD6YQ6AEIOzAG#v=onepage&q=sphere%20becomes%20eliptic%20camera&f=false
Any help or knowledge would be appreciated.