Monday, May 27, 2019

Nikon Micro-Nikkor, Nikkor 105mm ~ point light source comparison

For many years I looked at just one dimension of commercially available optics - resolution.  Now I continue to look at other aspects of optical performance.  For this series 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, +1 EV
  • Big Beefy Manfrotto tripod
  • Lenses using with a Lens Turbo II focal reducer -
    • Nikon Micro-Nikkor 105mm f/4 Ai
    • Nikon Nikkor 105mm f/2.5 P pre-Ai (early Sonnar design)
    • Nikon Nikkor 105mm f/2.5 Ai (later modified Sonnar, slightly more symmetrical design)
  • 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 105mm Point Lightsource Comparison

Comments -

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

 I had expected the Micro-Nikkor to show similar neutral very smooth out of focus rendition to the pair of 55mm Micro-Nikkors I looked at.  Alas, this is not the case.

These three Nikon Nikkor, Micro-Nikkor 105mm f/4 and f/2.5 P pre-Ai and Ai lenses show under corrected spherical aberrations.  At the point of focus, the Micro-Nikkor is one of the sharpest lenses I've looked at.  But that's not what this comparison is about.

In normal photography I would expect, based on these comparisons, that there will be a very smooth and delicate (to use Nikon's own word on the topic) out of focus field rendition, with the f/4 Micro-Nikkor showing a stronger "condom ring" (which will contribute to a distracting out of focus rendition) than the two f/2.5 lenses (compare the smooth, rounded edges of the out of focus disks of the f/2.5 lenses against the sharp edged disks of the Micro-Nikkor).

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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