Monday, June 03, 2019

Nikon Nikkor 85mm f/2 and f/1.8 ~ point light source comparison

For many years I looked at just one dimension of commercially available optics - resolution.  With this blog entry I continue to look at other aspects of optical performance.  For the series of postings I look at under, neutral, and over corrected spherical aberration in out of focus rendition on subject matter behind the point of focus.

Setup -
  • Sony NEX5T, ISO 100, 2 second timer
  • Big Beefy Manfrotto tripod
  • Lenses using with a Lens Turbo II focal reducer -
    • Nikon Nikkor 85mm f/2 Ai
    • Nikon Nikkor 85mm f/1.8 K pre-Ai
  • NOTE1: Lenses were shot at their widest apertures only
  • NOTE2: Out of focus samples are from points _behind_ the point of focus to compare background out of focus rendition
  • RawTherapee to convert RAW files into black and white and to set the black levels
  Comparison -

If you click on the following image you can inspect it at 100 percent.

Nikon Nikkor 85mm lenses ~ Point Light Source Comparison

Comments -

NOTE: I feel the Lens Turbo II focal reducer adds a bit of under-corrected spherical aberration.

The Nikon Nikkor 85mm f/2 Ai lens shows under corrected spherical aberration as well as a bright edge ring that suggests over correction around the outside of the out of focus disk.  In normal use, I expect the out of focus rendition to be "harsher" than, say, the next lens from Nikon.
The Nikon Nikkor 85mm f/1.8 K pre-Ai lens shows classic under corrected spherical aberration with a bright dot in the center of a smooth disk.  In normal use, I expect the out of focus rendition to be "delicate" (using Nikon's own description of the effect) and smooth across the field.

Resources -

For further information on how the topic of out of focus rendition, optical properties, and Nikon lens design history, please refer to the following -

A PhD thesis on the impact of "soft focus" lenses on the history of photography -

An excellent starting point for understanding out of focus rendition (I might not completely agree with his interpretations/observations, but his foundation of understanding is quite good) -

Nikon lens design histories -

Point light source discussions -

Zeiss comments on optical design -

Metabones Focal Reducer whitepaper -

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