Focus stacking is a common technique used by landscape photographers for images in which ultra-deep depth of field and high levels of sharpness are desired. You can use it for nighttime landscapes that incorporate things like the Milky Way as well, though it takes some additional considerations. This excellent video tutorial will show you a workflow for the technique as well as offer some helpful tips to ensure you get the best quality images.
Coming to you from Milky Way Mike, this great video tutorial will show you how to use focus stacking for nighttime landscape images. Focus stacking is a very useful technique for landscape photographers, as it allows you to ensure you get maximum sharpness across the entire depth of the image without running into issues with diffraction from using too narrow of an aperture. It can be a bit more challenging when shooting at night, however, as you will likely vary not only your focal point, but some exposure settings as well, since you can only shoot the sky without a tracking mount for so long before it will start to blur, while you can afford to expose the ground for much longer in most situations. Check out the video above for the full rundown.