Pentax K-500 has a Pentax KAF2 lens mount and currently there are 148 native lenses available for this mount.
K-500 also has a sensor based image stabilization system which means that all of these lenses will be stabilized when used on K-500.
Since Pentax K-500 has a APS-C sensor, it has a focal length multiplier of 1.5× so you have to multiply lenses original focal length with this multiplier to find the Full Frame equivalent focal length of the lens when mounted on K-500.
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Pentax K-500 Lenses with Image Stabilization
Pentax K-500 Lenses with Weather Sealings