 For that reason, when using the manual aperture ring on K-mount lenses, it is necessary to set the 'Use aperture ring' setting in the 'Custom Menu' to 'Permitted' and use stop-down metering mode (Pentax calls it optical preview) to ensure proper exposure.KA and KAF lenses with aperture rings are fully compatible when the aperture ring is set to automatic ('A'), giving control over the aperture to the camera body.Under a partnership between Pentax and Samsung Techwin, the K10D is also available badged as the Samsung GX-10.