模糊圈，摄影术用语，又叫弥散圆(circle of confusion)。

点光源经过镜头在焦平面成的像是一个点，保持镜头与底片距离不变，沿光轴方向前后移动点光源，像平面上成的像就会成为有一定直径的圆形，圆形的大小取决于镜头孔径和点光源偏离程度，只要这个圆形像的直径足够小，相片看去仍然够清晰，点光源圆形像再大些，相片会显得模糊，这个临界点光源圆形像，就叫模糊圈。

在焦点附近，光线还未聚集到一点，点的图像成为模糊的一个圆，这个圆就叫做弥散圆。 在现实当中，观赏拍摄的图像是以某种方式(比如投影、放大成照片等等)来观察的，人的肉眼所感受到的图像与放大倍率、投影距离及观看距离有很大的关系，如果弥散圆的直径小于人眼的鉴别能力，在一定范围内实际图像产生的模糊是不能辨认的。这个不能辨认的弥散圆就称为容许弥散圆(permissible circle of confusion)。

In optics, a circle of confusion is an optical spot caused by a cone of light rays from a lens not coming to a perfect focus when imaging a point source. It is also known as disk of confusion, circle of indistinctness, blur circle, or blur spot.

In photography, the circle of confusion (CoC) is used to determine the depth of field, the part of an image that is acceptably sharp. A standard value of CoC is often associated with each image format, but the most appropriate value depends on visual acuity, viewing conditions, and the amount of enlargement. Properly, this is the maximum permissible circle of confusion, the circle of confusion diameter limit, or the circle of confusion criterion, but is often informally called simply the circle of confusion.