Bokeh

Long time between posts. But this is a short one about bokeh. For me it has two qualities - the aesthetic look and the degree of blurring. The former can only be decided on a per lens basis and is highly subjective. The second factor, which is degree of blurring, is primarily based on the objective size. That is, the true aperture size. The larger the physical size of the diameter, the more the blur. For example, a 50mm f/2.0 has an aperture size of 25mm. A 200mm f/2.0 lens has an aperture size of 100mm. In most circumstances (i.e., same image size) the blur on the 200mm at f/2.0 will be far more than the 50mm f/2.0.

Given this, and the fact that I love blurred out background, I can make an informed choice between lenses as to which one will give me the most blur - but not necessarily the most beautiful blur. Some interesting conclusions is that the smaller the format, the larger the aperture needs to be to have good background blur.

In principle, my choices of lens for bokeh (for full frame D700) ranges between 50mm to 300mm. In this example, the following is a measure of the theoretical aperture size for various lenses. Noting that the large the aperture, the more blur.

50mm f/1.0 = 50mm (e.g., Leica Noctilux)

50mm f/1.4 = 35mm

85mm f/1.4 = 60mm

85mm f/1.8 = 47mm

100mm f/2.0 = 50mm (e.g., Zeiss ZF2 Planar)

135mm f/2.0 = 67mm (e.g., Zeiss ZF2)

200mm f/2.0 = 100mm (e.g., Nikon 200mm f/2.0 )

200mm f/2.8 = 71mm (e.g., f/2.8 70-200 zooms)

300mm f/4.0 = 75mm (e.g., Nikon 300mm f/4.0)