Sharpness and blur

As we learned in the section „Stereoscopy“, the objects on the horopter appear sharp to us, while those in front or behind appear blurred and out of focus. From this fact we can learn that it is not possible for us to see objects at different distances in focus at the same time. We often overlook this because it’s so common and familiar to us, but if you focus, you’ll quickly notice that the distribution of sharp and blurred objects in the visual field allows us to draw precise conclusions about the distribution of objects in space.


Actively try it once. Looking out of the window will certainly reveal to you a multitude of objects at different distances from each other, such as houses, trees, bushes and people. Select a pair of objects that are not too far away from you and each other, and that are as precisely positioned in one plane as possible. First, look at the back of the pair to see it clearly. In this constellation, the front object will appear blurred and somehow transparent to you. By this, I mean that the background shimmers through a little. Then change focus and bring the front object „in focus“. The blurriness and transparency effect will now move to the back. Finally, try to see both objects in focus at the same time. You will quickly notice that this is not possible. At short and medium distances, our eyes‘ depth of field is not large enough. We can only perceive parts of the landscape that are far away from us in sharp focus at the same time. Sharp and blurred objects in the same line of sight allow us to draw the conclusion that these things are at different distances, giving us an impression of spatial depth.

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Main Image creation, Depth and Size

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