4

While you can get good results from a single exposure, you can reveal even more detail by combining four or five exposures. Then you can manually combine them as different layers in Photoshop.

The stars will have moved over the course of these exposures, so you will have to carefully align the images so that stars line up. Now halve the Opacity of each layer compared with the layer below it. So on the first layer above the background, set Opacity to 50%, 25% on the layer above, 12% on the next, and so on.

If your shots include any foreground or land, these areas will now be mis-aligned. So you will need to add a mask to each layer, and carefully paint over the areas of the mask using a black brush where these areas appear in the top layers. Then only the landscape in the background layer is visible. As a finishing touch, combine it with an image where you set the exposure for the landscape or foreground. Add this as a layer on the top of the layer stack, add a mask and carefully paint out the areas of sky using a black brush.

Above Wave a large torch across a foreground object to make it stand out in your starscape shot.