Follow up on the discussion of focus error on the 50mm f/1.2 AIS
Since writing and posting my review of the aforementioned lens, I have had a few correspondences with Lloyd Chambers. So first I would like to extend my gratitude to him for taking the time out of his busy schedule in helping me understand this problem better. His generosity and patient were will appreciated by this author.
The problem I encountered trying to focus at f/1.2 (actually this can be at other aperture setting, stopped down to f/5.6) appears to be spherical aberration. It would be redundant to of me to repeat his articles, so I will just provide here the links. http://diglloyd.com/diglloyd/index.html &
As to my findings and opinions, I can say this much. To begin I must say I was wrong in calling the tests a ‘wank” for any reason. It is something that needs to be understood, if one wants to shoot with a “fast” lens at the wide apertures and get if not optimal then at least good results. Like Lloyd Chambers says, “sparkling-sharp eyes versus not-quite-there eyes”.
These fast lenses, like the 50mm f/1.2 AIS all have some spherical aberrations inherent in their optical design. There are of course aspherical corrected lenses that can eliminate the worst of the problems associated with fast lenses. These of course do not come cheap. The thing is you either like the results of a lens like the 50mm f/1.2 AIS or not. I for one do like the results, both wide open and stopped down. It really is two different looks. And from that perspective I do recommend the lens for people of similar tastes as mine. However for most people there are some much better alternatives, with or without auto-focus and at varying price ranges. For those that choose such a lens, then it is a must to “learn” the lens and it’s peculiarities. It is work, but then the rewards can be worth it.
In my review I mentioned that I had set focus to a point where the focus confirmation “dot” and the right side arrow were both flickering, when exposing at f/ 1.2 (this is the inherent problem of a fast lens wanting to back focus). This technique was my way of manually correcting the problem. Under most other circumstances I found using a “solid green dot” at aperture settings of f/2 or smaller, worked just fine. It was not until I enlarged the image to 400%, that I saw enough of a difference. In my line of work I cannot afford to be so critical. The emotions of the moment is my main concern. However possessing this knowledge and how to correct or make the proper adjustments for it, is quite essential and not a “wank” as previously stated.
For this follow up I have included a few more examples all shot at f/1.2 and one or two comparison shots at f/2.0. Many thanks again to Lloyd Chambers.