field curvature, MTF, Zeiss Distagon, focus accuracy
To Making Sharp Images I’ve added/revised two pages:
- MTF Measurement vs Field Curvature (technical discussion)
- Field Curvature Focusing Tips (technique and example)
Both of these should be helpful for the photographer looking to extract maximum performance from high-resolution cameras, regardless of brand.
This example uses a Zeiss lens with modest field curvature: the 25mm f/2 Distagon.
More severe cases
As shown below, the deep dip/wave with the Leica 35/1.4 Summilux-M ASPH FLE is a prime example of a lens whose field curvature is strong enough to have a serious impact on across-the-frame sharpness of planar subjects such as a wall/building or a distant infinity scene: focusing slighty differently to take this into account can in some cases mitigate the loss of sharpness in the mid zones.