Re: 24-70/2.8L II field curvature (is this normal?)
There is one other thing to think about here. It is a bit difficult to describe in words, but here goes.
Let\'s start by noting that the camera is angled downwards in this photograph. Keep that in mind.
Modern lenses are designed not so that everything some single distance from the camera will be in focus, but so that a plane parallel to the sensor will be in focus. Imagine the following. You are standing off to the side of the photographer. Let\'s say that 25 feet out in front of the photograph is the plane of optimal focus. Imagine something like a wall at that distance from the camera. Note that portions of the wall further away from the center point on which the photographer is focusing are actually a slightly greater distance from the camera.
Now imagine relocating the focus point in the center of the frame downwards. The plane of optimal focus is still parallel to the sensor, but since the camera is tilted down that focus plane is also on an angle — further away from the photographer\'s position that it was before in the upper part of the frame, and closer to the camera in the lower part. Things get even stranger if you focus on a point that is not in the exact middle of the frame...
The simple point is that you get a flat field of focus that is vertical only if the camera is aimed exactly straight ahead. Tilt the camera down and the focus plane also tilts, focus on a point other than the center point and the effect can be magnified.
Dan
Jeff wrote:
So, once again, after getting home from a 15-day road trip I\'m finally getting a chance to take a critical look at images from several new lenses and bodies. As one would expect from the title of this thread, I\'m seeing massive field curvature from the 24-70/2.8LII, especially in the middle of the zoom range, even at 5.6.
An example is provided below; I went through the image from one side to the other at 1:2 and put a mark where the plane of focus seemed to be. 100% crops showing different areas of the image follow.
I owned the Mark I version of this lens and never noticed such extreme curvature, and it was, in fact, my go-to lens for group portraits (which I also need this lens to be). As you can see from the plane of focus, I\'m not sure how anyone could get any sort of group portrait without lining them up along said \'line in the sand\'. And for what it\'s worth, some landscapes at 24mm and focused out towards infinity exhibited soft left and right sides as well (f/5.0), similarly alarming for me given how most contend that this lens is sharp from corner to corner. In other words, I\'m thinking that this lens just can\'t be \'right\'.
Has anyone else seen such pronounced field curvature from this lens? It\'s going back for a replacement, but I\'m wondering how likely I am to get the same thing back, as some of this is almost certainly lens design, to some degree.
Thanks,
Jeff
Aug 19, 2015 at 09:13 PM
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