Varying optical frequencies

Source: Pictures taken of "Fall" (1963) by Bridget Riley as exhibited at the Tate Modern Museum.

I love the optical illusions and tensions created simply by varying the optical frequencies. I love the way the lines seemingly move through space by way of the repetition, and increase and decrease in speed. What a bitch to make. Props to Riley for her patience, vision, perseverance and skill.  

Here are some of her other pieces:

Source: Barton Galleries "Movement in Squares"

Source: Op Art "Ease" (1987)

Source: Op Art "Loss" (1964)

Source: Art "Blaze"

Source: Abstract Art "Breathe"