I am trying to visualize this better and could use some help please. Let's say you have 2 identical spherical lens blanks. In one, you grind the back to produce a conventional plus lens. On the other, you grind the back at an angle to produce a plus lens with prism. On the first lens, the optical center is at the thickest portion of the lens. On the second lens, however, the thickest part is skewed toward the edge and no longer coincides with the geometric center. So what I am not getting is what defines the optical center of the second lens with ground in prism? Is there still some point which can be identified where light will pass straight through? I just cannot visualize where this would be. Thanks.

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