If you follow this blog, you’ve seen photos taken with decentered SLR camera lenses, on the Sony a7R. Those photos typically show a lot more blur on one side of the image.
So if lenses can be that bad, what about the adapters that they are mounted to? Can the cheap NEX emount adapters be crooked somehow, and cause decentering? There is a ton of hype surrounding this issue. Lets just cut to the chase, and sum up the two photos below. All shots were taken with the Sony a7R.
The first picture combines horizontal sections of two photos, both taken with the same Canon FDn 24mm f/2.8 lens, shot at ~f/10. That lens was mounted on a generic FD to NEX emount adapter and a Fotasy FD to NEX emount adapter. Both pictures are nearly identical, so at this ~f/10 aperture, neither of the emount adapters appears to be having any effect on the picture.
The second picture combines horizontal sections from four photos, same aperture, taken with a Tamron 28-70mm Adaptall-2 zoom, model 159A, shot at 28mm. That lens is not one of the Tamron SP lenses, but it uses the same Adaptall-2 adapters. So three out of the four sections of this second pic were shot using a combination of Adaptall-2 adapter and NEX emount adapter. Stacked adapters like that have to be the worst-case scenario, right? Won’t all that “misalignment” cause major decentering?
To recap this second photo: one lens, four pics sliced together, shot using seven combined adapters.
Well, as it turns out, the lens was already heavily decentered on the left-hand side, it’s a blurry mess; all of those stacked adapters didn’t magically move the decentering effect over to the right side, because cheap adapters don’t have any glass to alter the path of the light coming in.
The first horizonal slice is probably the worst, largely because the center focus point on the “5610″ address number was slightly off. As we saw with the Konica Hexanon 24mm f/2.8 lens, a very slight center misfocus with certain lens designs, can have a significant effect on how field curvature affects the sides of the image. The remaining three horizontal slices are more consistent, but still not perfectly identical. This Tamron lens was difficult to focus, because it has a long focus throw, in the critical focus area, so this Adaptall-2 exercise needs to be repeated with a different lens design.
As always, view these photos at 100% full size: