Saturday, May 25, 2019

Sigma 19mm, 30mm, Sony 50mm ~ point light source comparison

Having looked at the out of focus rendition of vintage Nikon lenses, I wanted to see what, if anything, had changed over the years of optical design and look at three current lenses.

Setup -
  • Sony NEX5T, ISO 100, 2 second timer, +1 EV
  • Big Beefy Manfrotto tripod
  • Lenses designed for Sony E-mount APS-C cameras -
    • Sigma 19mm f/2.8 EX DN E
    • Sigma 30mm f/2.8 EX DN E
    • Sony 50mm f/1.8 SEL OSS
  • 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.

Sigma, Sony APS-C Point Lightsource Comparison

Comments -

The Sigma 19mm f/2.8 EX DN E out of focus rendition confuses me.  There is a slight bright ring around the out of focus disk, along with a bright center with a dark whole in the middle.  The further out of focus the point, the more "choppy" the disk becomes.  Concentric circles form the farther out of focus the disk becomes.

The Sigma 30mm f/2.8 EX DN E out of focus rendition confuses me just like the 19mm Sigma does.  There is a bright outter ring to the disk, followed by a brighter center with a dark hole in the middle.  The "choppy" field effect across the disk is less than with the 19mm, but it's still clearly visible.

The Sony 50mm f/1.8 SEL OSS starts out having a nice smooth disk with a brighter center just like the lens is under-corrected.  But the further out of focus the point is, the stronger the outter ring becomes.  It's as if the Sony lens is both under and over-corrected.

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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