Axial CA on 85mm f/1.2L II

[interactii]

Hi everyone! I've managed to pick myself up an 85mm f1.2 II Lens, and I'm trying to learn a little more about this amazing piece of glass.


Below is one of the first shots I've taken with this lens with my 7D. The thing that is surprising me is the axial CA. Areas in front of the focal plane are suffering from magenta CA, whereas areas behind the focal plane are suffering from a lesser blue\green CA. This particular shot is at f/1.4.


I don't really have much experience with really wide-aperture lenses, most everything else I use is f/2.8. Is this kind of thing typical of wide-apertures? Of the 85mm f/1.2 II, or perhaps this copy specifically? I don't have much to compare it to. This CA disappears by f/2.0 or so, but winder it is visible in almost everything, even low contrast images.


Anyone have similar experiences with this or other wide lenses? What lens would you have chosen to capture this scene in a similar way?


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[Shea Design]

Hhmmn,, saw this in the review:


All three copies of the Canon EF 85mm f/1.2 L II USM Lens I have used
to date show more CA (Chromatic Aberration) than the older 85 L.
And my 85 f/1.8 shows less CA than either version of the 85 L lens.
The 85 II lenses I have used are producing noticeable CA at the widest
apertures when sun glares from something reflective in the shot (such
as a chrome car bumper).
For most applications, the CA will not be a big deal - and removing it
in post-processing is often possible.


Seems it is the nature of the beast. Maybe ND filter a few stops.

[Keith B]

All my fast lenses produce quite a bit of CA. I think the 35L is the worst but is only a problem with certain shots like you very high contrast edge shot there. I haven't played with the 50L enough to compare it's CA. I think my 85L would probably kick out similar CA. Maybe even worse, I'm not sure how or if a FF sensor affects CA differently.

[Garrett-Grimsley]

CA is the price you pay for having such a nice aperture, sadly.

[neuroanatomist]

Is this kind of thing typical of wide-apertures? Of the 85mm f/1.2 II,


Yep - pretty much every wide-aperture lens. It's just physics - light travels at different speeds after refraction through a lens. Lenses are designed to focus green light on the sensor; as a result, red light is focused a little behind and blue light a little in front, and this is most evident with the ultra-thin DoF you get with a wide aperture.


This shot from photozone.de's review of the 50mm f/1.2L should look familar:


http://www.photozone.de/images/8Reviews/lenses/canon_50_12/fringe.jpg

[interactii]

Wow. Good to know. The last time I used such wide apetures was on 35mm B&W where CA was less of a problem. Thanks for your insight everyone! I also can't understate how important calibrating the focus was with this lens, the sharpness went from "ho-hum" to "holy cow" in 15 AF micro adjustment steps :D