Double image in out-of-focus background (Canon EF 85mm/f1.2L II USM)
Related: Canon, Canon EF, Canon EF 85mm f/1.2L II, Canon Lenses, focusing, optics
In researching a new article, I came across an interesting form of chromatic aberration with my new Canon EF 85mm/f1.2L II USM. By the way, I consider the upgrade well worth it. Though the focusing speed remains relatively sluggish and difficult to use for action, it’s a welcome speedup over the older model.
At f1.2, a magenta/green double image begins to appear about 60% of the way from the optical center to the edge of the frame. The effect is symmetric to both the left and right sides (my test was also about 10% below the vertical center of the frame).
The target patches shown below were behind the plane of focus as indicated, and also away from the optical center as indicated.
| Canon EF 85mm/1.2L II USM on Canon EOS 1Ds Mark II f1.2, 1/125 sec, mirror lockup |
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| 45mm behind plane of focus 65% from center to right edge |
65mm behind plane of focus 80% from center to right edge |
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Whether this is normal, or whether it indicates a problem with the lens is unclear. I suspect it is normal behavior related to the type of optical focusing the lens employs. Until I can test another sample, I won’t know for sure.
The double image seems to be a form of chromatic aberration, probably induced by the optical formula outside the plane of focus, since I haven’t observed any color fringing on in-focus subject matter. The color fringing is plain to see in other out-of-focus areas of the image as well.
It is disappointing that Canon didn’t completely eliminate chromatic aberration with this new version of the venerable 85mm/f1.2L. Canon’s terse press release notes only faster focusing, though sites like robgalbraith.com and dpreview.com state that the new version is “the same optically as its predecessor”. This claim appears to be contradicted by Canon’s own lens specifications. However, the apparent contradiction might simply be incomplete or poorly-explained specifications, rather than an actual difference.
Canon’s web site symbols indicates that the new version contains 3 aspherical elements and 1 “Super UD” element, whereas its predecessor indicates just one aspherical element. [See the online lens brochure, page 38, for an explanation of the symbols that Canon displays for its lenses]. Additional data was gleaned from Canon’s EF Lens Work III (well worth having in your photographic library, even if you’re not a Canon shooter).
| 85mm Lens features* | ||
| Technology | EF 85mm/f1.2L USM | EF 85mm/f1.2L II USM |
| Super UD element | 0 |
1 |
| High refraction elements | 2** |
0** |
| Aspherical lens elements | 1 |
3 |
| “Inner Focusing” (“I/R”) | unclear** |
yes |
| Floating lens element (focusing) | yes |
yes |
| Full-time manual focusing | yes |
yes |
| Circular Aperture (CA) | no |
yes |
| Super Spectra coatings | no |
yes |
*As indicated by Canon’s USA web site, lens brochure, and EF Lens Work III
** missing or conflicted data
Canon’s book “EF Lens Work III—The Eyes of EOS”, page 59 indicates “one large diameter ground and polished aspherical element” and “two high-refraction glass elements” for the original 85mm/f1.2L. Canon’s current (July 2006) online lens brochure says nothing about UD or Super UD lens elements in the original 85mm/f1.2L. There is also an Eyes of EOS CD-ROM, which I haven’t used.
I suppose it’s hard to complain much, since it’s already a one-of-a-kind lens with overall outstanding performance!
