While visiting Louvre Museum in Paris, you admire "Mona Lisa" through a -3.50D cylinder at two different orientation. The two different views are shown below. What is the orientation of the lens in view I and view II?

View I

vvvvvvvv

View II

 

Answer
The lens is orientated at 180 degrees in view I and at 90 degrees in view II.

Remember that the axis is 90 degrees to the positive power of

the cylinder (refer to question 4 in mock examination 15) but 
parallel to the negative power of the cylinder. In view I, the picture
is enlarged (elongated) in a horizontal position ie. 180 degrees 
and in view II, the picture is enlarged (elongated) in a vertical position ie. 90 degrees.