I am often bemused by writers who put themselves forward to unwitting acolytes or pupils as photography experts, trying to define both the techniques and the technology of the industry/craft/art. The definitions they proffer do not lend themselves to improving a novice’s results; not if the novice wishes gain an accurate understanding of photography and eventually improve. On the other hand, if a lesson is intended merely for dilettantes, then say so! Don’t label your lesson with hubris as “The Ultimate Tutorial.”

A lens’s aperture is rarely located at the back of a lens. It is more often found toward the front element. (Practically all camera lenses are compound, with multiple glass elements.) But that’s neither here nor there. I’m sure there is an exception. The most egregiously misleading part of your article, however, professes that “bokeh” is governed by the amount of light striking an image sensor (or film). That is flat-out not true.

Bokeh, notwithstanding the effects of digital image manipulation, the application of a supplemental glass filter to distort what’s in front of a primary lens, or the insertion of a cut-out mask (aka a cucoloris, or “cookie”), the effect you’re writing about is the result of an optical property known as depth-of-field; i.e., commonly defined as the distance between the closest and farthest objects in a photo that appear acceptably sharp in a photograph. By the way, depth-of-field refers also to what’s in the foreground, as well as the background.

Aperture may be the first thing photographers think of when adjusting depth-of-field, but it’s not the only factor. The distance between the camera — actually the camera’s image plane (of focus) — and the subject has just as much of an effect on bokeh. The shorter that distance, the shallower the depth-of-field. Without getting into a boring technical thesis, the focal length of a lens, in combination with the size of a sensor (or the film) is just as influential in determining depth-of-field — or bokeh.

Depth-of-field is also affected by the relative distance of a camera — again the focal plane of its image sensor or film — from the subject a photographer wishes to keep in sharp focus. There is an optical term for this, or scientific jargon if you will: “circle of confusion.” That’s not meant to confuse you.

One more thing: camera movements — also known as “tilt-and-shift” — affect the relative sharpness of foreground and background objects to the subject of a photograph. This, too, affects DoP. It produces what you generally refer to as a bokeh effect.

Don’t get me started on the “locus of focus,” or any other hocus pocus, involving the mathematically elegant Scheimpflug principle, which governs the optimization of depth-of-field in tandem with perspective by using tilt-and-shift.

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