Nikon is excited about its latest lens, the Nikkor Z 135mm F1.8 S, even more so than usual. It's gone as far as to give the lens a name, Plena. It's the second named Z lens, following the 58mm F0.95 S Noct, an $8,000 lens that is more about what Nikon's engineers could do with an unlimited budget, and less so a practical tool for mere mortals.
The Plena is a more approachable lens; it costs about a third of the Noct, and includes autofocus, so we expect more photographers to actually own one. Its focal length and aperture make it an especially good pick for portrait work, or any photo where you want to place your subject against a blurred, defocused background.
The 135mm F1.8 isn't a unique concept, Canon and Sony both sell a version for their respective mirrorless systems. Nikon is touting a couple aspects of the Plena as difference makers versus the competition. Its 16-element/14-group optical formula uses a single aspherical element, which makes for rounder bokeh highlights toward the edges of the picture at f/1.8. Both the Canon RF 135mm F1.8 IS L USM and Sony FE 135mm F1.8 GM exhibit the cat's eye effect toward the periphery.
For stopped-down work, an 11-blade aperture maintains rounded highlights at smaller f-stops. Nikon also touts a minimal vignette as an advantage, though lens correction profiles make that more of a bragging point than practical concern for most photos.
Autofocus is a practical addition that's not included in the Noct; the Plena's STM motors work with eye detection and tracking features included in Z mirrorless cameras, so you should be able to get perfectly focused eyes, even if your model is moving. Stabilization isn't included, however, so Nikon photogs will need to be more mindful of
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