If you think that your render lacks sharpness (which i think it does not), then standard procedure is to apply it in post, either in Corona VFB, or externally in photoshop or somewhere else. There's no render setup that would make your renderer significantly sharper, but there are some settings that may help you in certain areas. For example, if you think that your textures are too blurry, then you should look at bitmap filterring and blurring settings in each texture node. On the other hand, if you feel that overall image is a bit too soft (especially on high contrast areas), then you can try to decrease image filterring radius in render setup and/or change image filter type to a sharper one. In any case, don't expect to see significant changes. If you need even more sharpness, then as i said above, apply it in post. All in all, it's always good idea to render a little bit softer and apply sharpening later. Remember - you can easily sharpen soft image in post, but it's much harder to soften oversharpened image.