Factors affecting bokeh
The number and shape of aperture blades
The arrangement of the lens aperture affects not so much the quality of the blur as the shape of the blur circles. In fact, so-called blurring circles rarely have a perfectly round shape. They usually look like more or less regular polygons with the number of sides corresponding to the number of diaphragm lobes. The aperture in Nikon lenses has 7 or 9 lobes, in Canon lenses – 6, 7 or 8 (occasionally 9). The more petals there are, the more rounded the blurring disk looks, and an odd number of petals usually produces polygons that are more pleasing to the eye.
In modern lenses, the aperture lobes are increasingly given a slightly curved shape, which makes the sides of the scattering polygons convex and thus visually brings the polygon closer to the circle. 9 rounded petals give an almost perfectly round bokeh.
If the photo is taken with the aperture fully open, then the blur spots on the edges of the frame will become oval or even lentil-shaped, while remaining completely round in the center of the image.
Design features of the lens
Defocus Control Nikkor is a pair of portrait telephoto lenses (AF DC-Nikkor 105mm f/2D and AF DC-Nikkor 135mm f/2D) manufactured by Nikon since the early 1990s and equipped with a mechanism that allows the photographer to directly control the nature of the bokeh, varying the degree of correction of spherical aberrations. This allows you to fine-tune the blur for either the foreground or background, as well as for specific aperture values.
Sony (Minolta) 135mm F2.8 T4.5 STF – specific telephoto lens with manual focus and apodizatsionnym element that provides a very smooth background blur.
Mirror-lens lenses (Reflex-NIKKOR, Rubinar, etc.) give bokeh in the form of clearly defined rings or bagels. The effect is purely for the Amateur.
Anamorphic lenses and attachments are used in cinematography and allow you to find yourself on the characteristic bokeh in the form of elongated ellipses in the vertical direction.
If your lens or camera is equipped with an optical image stabilizer, it is highly desirable to disable it in cases where you want to get the perfect bokeh. Most stabilization systems tend to give areas that are out of focus a somewhat restless appearance.
The more contrasting the background and the brighter the glare, the more clearly the blur discs are visible and the sharper their edges. The most obvious side is obtained when photographing the city at night or the sun’s rays pierced the foliage.
Color of out-of-focus objects
The degree of spherical aberrations varies for light waves of different lengths. As a result of spherochromatism, i.e. the chromatic difference of spherical aberrations for rays of different wavelengths, the edges of the scattering spots in the background acquire a blurred border of green, and in the foreground-the same border, but of a crimson color. This effect is especially noticeable when using lenses with a large focal length with a wide open aperture. An interesting consequence of spherochromatism is that bokeh turns out to be especially soft and beautiful when the background in the photo is green. Hence the appeal of open-air portrait photography.
Finally, let me give you a little advice: do not turn the pursuit of beautiful bokeh into an end in itself, as is often the case with beginners. No one forbids you to indulge a little, removing bokeh for the sake of bokeh, but this kind of fun quickly gets boring. Just remember bokeh as one of the expressive tools for low-depth-of-field photos, but don’t make an idol out of it.