Use of the front element

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This page illustrates misunderstanding number 10 on the misconceptions page. If lenses, at reduced apertures, only use a small central portion of the front element,

A lens with a piece of paper stuck on the front element.

Figure 1. A lens with a piece of paper stuck on the front element.

then from where comes the dark square in this picture?

Picture taken with the lens at f/22.

Figure 2. Picture taken with the lens at f/22.