Best portrait lens for the pentax k s1?

Here is what the site says about that.

From Pentax K-S1: Pentax K-S1: A DSLR by Pentax with a 20.1-megapixel APS-C sensor, announced in 2014. Specs - Maker: Pentax - Mount: Pentax K - Sensor: APS-C, 23.5 x 15.6mm, crop factor 1.5 - Resolution: 20.1 megapixels - Stabilisation: in the body - Announced: 2014 - Type: DSLR Focal lengths on it Lenses frame like 1.5 times their focal length on full frame: 16mm like 24mm, 23mm like 35mm, 33mm like 50mm, 57mm like ...

From Portraits: Portraits: For portraits, the lens matters far more than the camera. A cheap body with a good portrait lens beats an expensive body with a kit zoom every time.

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