The greater the number of diaphragm blades, the more perfectly circular the aperture becomes and - if these blades are slightly curved - the better the approximation to a circle.

If the diaphragm aperture is not circular, then the angular edges do not produce perfect circles and the bokeh appears slightly harsh, because the overlap is not smoothly accomplished. The figure is a 9-sided polygon with curved edges - and reflects the 9-bladed iris diaphragm that created it. At first I found them disconcerting, but then decided I liked them because they show the faint diffraction patterns at their edges, and because the diaphragm is not perfectly circular. In the photo above, distant highlights are caused by reflection from a water surface where the dragonfly perches on a stem. If the aperture is a perfect circle, then overlapping images blend beautifully and backgrounds look smooth - that's good bokeh.īlur circles with diffraction rings around them. They are actually diffraction patterns whose edges assume the shape of the lens aperture in the diaphragm through which they pass. We can think of these blurred area as over-lapping circular pools of light where rays have spread out rather than been focused. It is not just a figure plucked from the air, for it has a firmer basis in optics and the way we view prints - as I shall explain later. This measure was chosen as the diameter of the so-called 'circle of least confusion' with 35mm format film work. These are the so-called blur circles and, we are told, that as long as these circles are no larger than 1/30mm (originally on a 35mm film), then the average human eye cannot distinguish them from a point. The sharply focused parts of any image can be thought of as points or collections of points, but away from these - the out-of-focus areas - the light spreads slightly and those points become tiny circles. What might look like good bokeh to you and me, might very well not look good to others. And again, I must stress that bokeh is a highly subjective measure. That basic aesthetic will likely pass the test, though aficionados might well develop finer definitions and, naturally, a specific vocabulary to go with it. So, what constitutes 'good bokeh'? Well, I'd say a background where highlight blurs have soft edges and demonstrate no sharp distinctions between out-of-focus elements. It all comes down to perspective and the consequence of reducing three dimensions in the real world to the two-dimensional image on a print or screen. With wide-angle lenses you are much closer to a subject than with a telephoto. Lenses treat spatial separation of elements in a picture differently according to their focal length - a good exercise is to photograph a subject with a wide-angle lens and a telephoto and move so that it occupies the same proportion of the viewfinder. Meanwhile, telephoto lenses tend to isolate subjects from the background, and it is in that background that bokeh becomes important. Typically, a wide-angle lens will render a foreground subject sharp, as well as retaining detail in the background. )īokeh tends to be less noticeable with wide lenses unless you are shooting close to a subject at maximum aperture.

(My friend and fellow IR contributor Steve Meltzer sent me this, which seems appropriate. or American version) is a capricious tongue and someone is sure to correct you no matter how you say it. There are two syllables pronounced without noticeable pause between them: the bo (as in bone or boat) and a short ke (as in kettle or kelp) assuming that your pronunciation of these is standard. I'll put my photo nerd hat on and hopefully not offend you: The term is not pronounced boke (as in poke), or even bo-kay (as in Bouquet). Much has been written since then, including guides to the term's correct pronunciation - and explanatory YouTube videos - revealing how you, too, can be a photo nerd and leap to correct your (ex) friends. As far as I can determine, bokeh first appeared as a term relating to Western photography in recent history when Mike Johnston introduced it in an 1977 issue of Photo Techniques magazine.

Good vs bad bokeh examples