Sorry, no. If it fit onto a Pentax camera then the lens has a Pentax mount. The Nikon (I assume you mean the D80 digital camera, or perhaps the N80 film camera) has a Nikon mount. Since the Nikon mount has a deeper flange distance than the Pentax mount, there are no adapters available to allow you to fit a Pentax-mount lens onto a Nikon camera.
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Sorry, no. If it fit onto a Pentax camera then the lens has a Pentax mount. The Nikon (I assume you mean the D80 digital camera, or perhaps the N80 film camera) has a Nikon mount. Since the Nikon mount has a deeper flange distance than the Pentax mount, there are no adapters available to allow you to fit a Pentax-mount lens onto a Nikon camera.