When doing wide-angle photography at night sometimes the scenery is made even prettier if stars or constellations do show up in the picture. However in most pictures, the stars never show up as bright and colorful as they appear visually. Prominent constellations like Orion, Big Dipper, Cassiopeia etc are barely visible on the image - their stars are captured in the image, but the constellations do not stand out and are not eye-catching. Therefore, images of a starry night quickly seem boring as they lack contrast in the night sky.
The reason for that is that in such starry night pictures, bright stars hardly seem bigger / brighter than the other stars. Especially when the picture is well focussed all stars are rather white pinpoints, not revealing the colors of their nature any more.
So how do you make bright stars also appear bright?
How do you get those little colorful halos around the bright stars without losing too much detail?
One option for creating these colorful-star-effects is using a soft fog-filter in front of the camera lens. Below is one example of the same region in the sky with the constellations of Cassiopeia ('the W') and Perseus, taken just after another with the same exposure settings. You can clearly see the effect that a soft fog filter creates.
All stars seem to have the same brightness and constellations are barely visible. Also, all stars seem to have the same color: white
Now, bright stars are shown with a little halo making them much more prominent in the picture. Also, the halo has the natural color of the star, giving an extra bonus to the picture
Of course using such an additional filter does also take away some details and sharpness. Therefore when working with fog filters for starry night photography it is important to use rather soft fog filters. Stronger fog filters do enhance this 'halo-effect' but do also take away smaller details. The best compromise between contrast and details are soft fog filters.