Fisheye lens distorts straight lines into ridiculous curves. Straight lines, depending on where they are in the photo can be pulled a lot, a little, or not at all. The farther they are from the the center line of the photo, the more distortion there is. The closer the line is to the midpoint of the X or Y axis of the lens, the straighter the line will be.

Specification of our fisheye lens as follow: 
*37mm 0.42X fisheye lens;
*72mm,82mm 0.7X fisheye lens