The coin appears to be a perfect circle only when seen a front face, when rotated around an axis parallel to the face of observer, it changes from round to a thin ellipse and then finally turns out to be a horizontal line fig. 100.

Fig.100: Transformation of a coin from circle to a straight line.

Stood upright and rotated around a vertical axis it appears to be almost similar phenomenon as above.

Major Axis, Minor axis:

Fig.101: Ellipse from a circle.