Circles of Confusion

Circles of Confusion.

Maybe out of the few pictures taken today selecting this odd one had something to do with being the shortest day of the year. Or maybe not. Might have had more to do with a difficult to follow article I was reading on depth of field. It started ok then descended into some difficult maths stuff and concepts and image comparisons. The opening shots were .................

'Optical theory doesn't know about depth of field. There is a plane of perfect focus where the light rays emanting from any point will converge in a point in the image plane - or actually a very small blob, due to the remaining aberrations of the lens and the diffraction at the aperture blades. Everywhere in front of or behind this plane a subject is rendered more or less blurred, so with maximum sharpness at just one distance and varying degrees of unsharpness everywhere else, the notion of depth of field has no place: the area of sharpness has no depth.

But that is only theory. In practice, sharpness is in the eye of the beholder. Whenever we are appreciating an image, we are viewing an image of a certain size and from a certain distance, using eyes of limited acuity. Under any actual viewing distance there will be some small amount of unsharpness that passes as sharpness, simply because our eyes couldn't tell the difference. And if the image is small or far away, even a large amount of unsharpness would go undetected. Once we forego the lofty perspective of optical theory and adopt the viewpoint of an acutal human observer, we can stop worrying about optimum sharpness and happily make do with merely acceptable sharpness - any amount of unsharpness that is indistiguishable from sharpness. Acceptable sharpness can be expressed as the maximum diameter of a circle of confusion that is indistinguishable from a point, and if we apply this criterion the plane of exact focus expands to an extended zone of acceptable sharpness that is commonly known as depth of field.'

There were lots more pages and some mathematical formula.......... I'll need to read it a few times and even then I'm far from convinced I'll truly understand the finer points.

As to the picture, its not sharp. It's not meant to be. I was messing about at close range to try a few things out and ended up with lots of what I decided to call circles of confusion!!