Why don't modern aspherical lenses automatically have excellent coma correction?

Question

The Nikon Noct 58mm f/1.2 is often praised for strong wide-open coma control, and its reputation is frequently linked to its early use of an aspherical element. Since aspherical elements are now common and inexpensive even in entry-level lenses, why don’t modern fast lenses routinely match that level of coma performance? Is there something special about the Noct’s aspherical surface, or is lens design mainly about balancing coma against other aberrations and cost?

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Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

9y ago

user40937 · Accepted Answer

The Noct-Nikkor has earned its reputation on the wings of the community of internet photographers who don't know what coma is. Coma is the formation of comet-like shapes away from the optical axis. Coma has not been the dominant aberration limiting the performance of consumer lenses in a very long time. The Noct-Nikkor has a large amount of both axial and longitudinal chromatic aberration. Freeing these design variables allows the correction of the astigmatism that typically limits the performance of these lenses off-axis.

Additionally, the placement of the asphere on the front surface, as far from the aperture stop as possible, indicates that its role is to reduce off-axis aberrations. This asphere placement could be used in other designs, but having the front element be aspheric is very undesirable; it is the largest element, which makes it expensive to aspherize, and it is also the most exposed element, making it the most likely to be damaged. An aspheric surface is more sensitive than a spherical one, and it is highly preferred that it be protected in some way.

Why don't modern aspherical lenses automatically have excellent coma correction?

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