Optical design & performance
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Optical design & performance

The optical design comprises 14 elements in 11 groups. One aspherical element and two XA ('extreme aspherical') elements effectively minimize sagittal flare, also known as coma. Minimal coma is particularly important for a lens like this one that's expected to see wide use in astrophotography and nightscape applications. Our initial samples indicate that coma is indeed well-controlled.

Those XA elements also help the 14mm F1.8 GM lens achieve high central and corner to corner sharpness, even wide open. MTF charts (representing a 'perfect' instance of the design) indicate that contrast remains at nearly 100% wide open for most of the field, only dipping slightly at the extremes, but still never below roughly 95%. Central sharpness wide open is greater than 90%, remaining well above 80% for most of the frame, and only dimming slightly below 80% at the extremes. Take a look at our aperture series; you'll note impressive edge-to-edge sharpness even at F1.8.

The front XA element has a downright impressive amount of curvature that help it achieve these optical feats. As per usual with recent GM lenses, high surface precision of molds used to make aspherical elements ensures smooth bokeh without the presence of onion rings or hard edges.