What determines sharpness and blurring in an image? Bertram Hönlinger, optics expert at ZEISS, talks about the performance of modern camera lenses and the limits of what is technically feasible.
Mr. Hönlinger, in photography the topic of “sharpness” is touched upon time and again. What exactly does it mean?
Bertram Hönlinger: One of my colleagues once put it like this: “Focus is an out-of-focus term.” By that he meant that there is no clear-cut definition of focus in photography. We see the concept much more on the subjective level.
But you are an optics expert. So I am sure you have a very specific image in your mind of what focus means.
Focus is closely related to depth of field. As soon as I focus on a point within a shot, say the eyes of a model when I am taking a portrait, a focal plane is created that ideally runs parallel to the camera’s sensor. One point on this focal plane will appear as a single point on the sensor – or almost will. It is a different story with the details in my motive points which lie either in front of or behind this focal plane: the rays of light reflected by them do not meet at a point in the camera sensor, but are in fact spread across an area around the target point.
This is known as the circle of confusion …
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continue at Zeiss
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“The camera’s resolution capacity and the reproduction of micro contrasts makes all the difference when it comes to image definition.”