Vision & Eyesight: Image Formation
As with any image being formed, it takes two or more rays from the same spot on an object to cross or appear to cross. In this case, looking at two rays from the candle flame, we find that the rays cross right at the location of the retina. This image would be in focus. It is important to notice that the real image of the candle is actually upside down on the retina. Your brain actually takes care of flipping it so it seems to be right side up. Some experiments that have been done involve people wearing some glasses that make everything seem upside down. After a few days, their brain flips the image. If they take the glasses off, their brain, after a delay, will flip it right side up again.
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