*The eye's lens varies from " n " = 1.406 in the centre to " n " = 1.386 at the edges; as well as its lens shape, it also focuses light by being a GRIN lens.
32.
So, does each chamber of the compound eye have a different focal length and / or lens shape, allowing them to choose which images they " see " at any point, by ignoring the rest ? talk ) 17 : 34, 9 August 2011 ( UTC)
33.
With the implementation of nosepads in 1920, the three-piece style surpassed the pince nez in popularity; the new design allowed wearers to adjust the position of glasses on the face, and also permitted for a wide variety of lens shapes, with optometrists offering over 300 options by 1940 ( though variations on circles, ovals, and octagons remained most popular ).
34.
Then count the bridges : There are at least 19 in view on a good day, from the grand arch across the Ohio at McKees Rocks to the " Three Sisters " _ nearly identical eye-bar suspension bridges linking downtown with the North Side _ to the double lens shapes of the Smithfield Street Bridge, a shimmering blue wave rolling over the Monongahela.
