What is Bokeh
Wiki have a great description here : Lens Bokeh
“In photography, bokeh is the aesthetic quality of the blur, in out-of-focus areas of an image. Bokeh has been defined as “the way the lens renders out-of-focus points of light”.
However, differences in lens aberrations and aperture shape cause some lens designs to blur the image in a way that is pleasing to the eye, while others produce blurring that is unpleasant or distracting.
Bokeh is often most visible around small background highlights, such as specular reflections and light sources, which is why it is often associated with such areas.
However, bokeh is not limited to highlights; blur occurs in all out-of-focus regions of the image.”
I have been looking for a way to test this feature of my lenses for a little time, then at Christmas we put up some little led lamps as below. So using two different lenses one a Nikon 50mm f1.8 lens and A Mamiya 45mm f2.8 lens I took some images of the lights, with the lens as out of focus as I could get them.
I think that the images below clearly show the effects that are described in the Wiki link, seeing clearly the effects of the number of aperture blades and their shape.
The Nikon lens as seven blade but they are not curved , the Mamiya lens blades are curved. You can clearly see that the shapes created are very different.
Lens Bokeh examples
Mamiya Sekor lens
Nikom AIS Lens