Especially phase detect AF as it is using mainly off-center rays that converge outside of area of best focus. Bokeh esthetic is more important in most pictures where it is visible. Sharpness is not optimal, but sharpness is way too overrated.Implications of lenses with under-corrected or over-corrected Of under-corrected spherical aberration, displayed (again) below: If you ignore red and green coloredД®dges, it corresponds pretty well to the simulated sample There are red and green colored edges of bokeh - that is longitudinalД¬hromatic aberration. Camera is atДЄngle so that left side of LCD is farther than focus point, The test target is here: bokeh-test-lines.png (you can try it with your lenses)ДЄnd it is displayed on notebook LCD monitor. Real lenses do not behave like this, right? TheyДЄctually do. Now, this simulation above may look too artificial and Reversed in lens with over-corrected spherical aberration inД¬omparison with the original lens which was completely More detailed light field shows the bokeh appearance is Of equation was multiplied by 1.3 so the corrective effect stronger than it should be.Д®quation is x = 10*cos(alpha)+1.3*13*alpha^4 y = 10*sin(alpha). Next two images show another lens almost same as lens above,Д«ut with overcorrected spherical aberration. X = 10*cos(alpha) y = 10*sin(alpha) while the new aspheric surface has this equation: Specifically, the equation for original spheric surface Three surfaces of the two elements are same,Д«ut one has been changed from a sphere to a slightly differentД¬urve. Next two images show a different lens with two elements,ДЄlmost same as lens above, but with corrected sphericalДЄberration. Sensor would be at that position - that is the bokeh. Light field that show how would the light appear if image Next image below uses 800 rays that can overlap toДЄpproximate whole light field generated by that the single light Next image below uses white rays, but there are more of them to get better idea how this affects image plane. Rays are randomly colored so you can easily follow each Spherical so whole lens has spherical aberration with noД¬orrection. With material with refraction index of 1.5. Simulated (by my custom tool) has two biconvex elements, both Image below demonstrates spherical aberration. Image planes depending on whether the ray goes through center AnДЄberration that causes light rays to be focused on different Light source is not a point, but rather some foggy ball. So what should be a point in image plane as produced by point Single point light source to a single point in image plane (at Optimally corrected lenses focus all the entering rays from These basic types (red graphs show light intensity from the In light density around edges of out of focus highlights have It's a distribution of light inside of them. While shape of bokeh can be slightly distracting if it is notД¬ircular, there is another issue with out of focus highlights. Resulting shape is often a intersection of two non-concentricД¬ircles, often described as 'lemon shape' or 'cat eye'. Vignetting because the optical path in the lens is too narrow. The image has a lemon shape outside of center, gradually more Would be a circular out of focus highlight in the center of So what else goes into a character of bokeh? Sometimes what Rounded aperture blades are not guarantee of pleasing bokeh.

I have seen too often marketingД¬laim 'rounded aperture blades produce pleasing bokeh'. Sometimes a single blade is slightly misaligned and Lenses they may still be slightly visible in some aperture While the aperture blades are rounded in current Polygonal out of focus highlights (if aperture was slightlyД¬losed). Most of modern lenses have roundedДЄperture blades. This character is mainly given by opticalД¬onstruction of lens. The character of bokeh is best observed on small light On Bokeh Character What affects bokeh shape? Scene that is out of focus contributes to overall appearance.Д«okeh can be observed best on bright dots which are out ofДЇocus and surrounded by dark background. Effect of Electronic First Curtain Shutter (EFCS) on BokehД«okeh is a word which photographers use for an appearance of.Somewhat innovative methods to get nice bokeh.Comparison of Sigma 85/1.4 and Nikon 105DC f/2 on FX.Comparison of Sigma 30/1.4, Sigma 50/1.4, Nikon 50/1.4 on DX and FX.I plan to produce a part about bokeh size andДЄ part with some of my pictures related to bokeh theme later. The first part of article - On Bokeh Character - is

Bokeh lens