Doug Kerr
Well-known member
When a camera is not focused at the distance to an object, for a point on the object there is created at the focal plane not a point image but rather a blur figure, often called a circle of confusion. We find that phrase used in the names of three concepts.
A. Circle of confusion. The blur figure itself created at the focal plane from a point on an object at a distance other than that at which the camera is focused. We may use this to speak of a hypothetical blur figure that would arise from some particular situation.
B. Circle of confusion diameter. The diameter of a certain blur figure, perhaps a hypothetical one. It is a metric of the degree of blurring resulting from the presumed amount of imperfect focus. It may pertain to a hypothetical circle of confusion.
C. Circle of confusion diameter limit. The circle of confusion diameter that we consider to represent the greatest amount of blurring that we will consider "negligible". It may be of a hypothetical circle of confusion.
Now, in much writing, especially in the area of depth-of-field reckoning, the value of item C is called "the circle of confusion" (sometimes abbreviated CoC).
You can see that this practice makes it impossible to discuss items A or B.
I call the circle of confusion diameter limit the "circle of confusion diameter limit". I often abbreviate that as COCDL.
When all else fails, call it what it is.
Best regards,
Doug
A. Circle of confusion. The blur figure itself created at the focal plane from a point on an object at a distance other than that at which the camera is focused. We may use this to speak of a hypothetical blur figure that would arise from some particular situation.
B. Circle of confusion diameter. The diameter of a certain blur figure, perhaps a hypothetical one. It is a metric of the degree of blurring resulting from the presumed amount of imperfect focus. It may pertain to a hypothetical circle of confusion.
C. Circle of confusion diameter limit. The circle of confusion diameter that we consider to represent the greatest amount of blurring that we will consider "negligible". It may be of a hypothetical circle of confusion.
Now, in much writing, especially in the area of depth-of-field reckoning, the value of item C is called "the circle of confusion" (sometimes abbreviated CoC).
You can see that this practice makes it impossible to discuss items A or B.
If you call the largest diameter of wheel that can be used on a certain vehicle its "wheel", it is hard to talk about wheels and their diameters.
I call the circle of confusion diameter limit the "circle of confusion diameter limit". I often abbreviate that as COCDL.
When all else fails, call it what it is.
Best regards,
Doug