MTF vs Field Curvature and Tips for Optimizing Focus

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.

MTF for Leica 35mm f/1.4 Summilux-M ASPH