RECTILINEAR CORNER SHARPNESS
The Red Sea trip also gave me the chance to shoot the rectilinear 17-35mm in some more detailed field tests. As I elaborated in my D3 review, one of the potential downsides of FX is the blurred corners of wide rectilinear lenses, which have the potential to be more prevalent on the larger format.
With the D3 I was satisfied with the corner sharpness with this lens when shooting the great white sharks in Guadalupe. But I would be the first to admit that images with blue ocean in the corners is hardly a challenging test. Red Sea reefs would be a tougher proposition with plenty of detail that needed to be retained in the corners. I used the 17-35mm with a +4 dioptre behind a Subal FE2 dome and a port extension ring and shot several scenes at a range of apertures using the widest end of the zoom (17mm).
Crops (50%) from bottom left corner:
The corner sharpness results from the 17-35mm are better than I had expected. I shot subjects that I thought would highlight corner sharpness problems. I using the lens at the widest zoom setting, choosing subject matter close to the camera and lighting the entire frame, to reveal detail in the corner of the frame. I find these results completely useable at apertures of F8 and above and they even stand up well to a pixel peeping examination. As I found in my D3 review, this lens (or at least my port setup for it) is prone to chromatic aberrations on areas of high contrast (in this case tips of the fire coral). When I get a FX camera of my own I intend to experiment with my port setup and would expect to improve this performance further.
I also had another chance to experiment using the auto focus fine-tine feature to apply a focus offset, closer to the camera, for the 17-35mm in an attempt to improve corner sharpness. Frustratingly, the results were inconclusive really because the corner sharpness was so decent in the first place. In the end I could not tell any difference between the before images and the after ones, which suggests that first the effect is not very large and second I need some more controlled conditions to observe it. I’ll try and get the 17-35mm and a D700 or D3 in the pool soon.