Getting a good shot at night is difficult for a lot of reasons, starting with the obvious, darkness. There are only three ways to get more light to your sensor, increasing time, increasing aperture and increasing ISO.
Increasing time has the problem of creating star trails. My experience is that with a 35 mm lens, the Earth's rotation causes a star to appear to double it's length by 30 seconds unless you use a star tracker mounted on your tripod to compensate for the Earth's rotation. This problem is helped by using a wider lens. I can get away with 30 seconds (barely) when I use my 14 mm lens.
Increasing aperture is great up to a point. The widest aperture on most lenses comes with some optical aberrations such as coma and vignetting. It's usually best to stop down one stop from the widest aperture. The other issue is the shallow depth of field. Foreground items that are too close will appear blurred. The focal point should be on the stars in my opinion.
Increasing ISO increases the amount of noise in the final image. This can be reduced in post production using Bridge, Photoshop or Lightroom. We will cover that below.
What I want to do in this blog is describe how I process the night sky images. For this example, I will use an image I captured on a raft trip down the Grand Canyon. We were stopped for the night at a rapid named Lava Chuar. Despite a long day of rafting and hiking, we were up much of the night doing more photography. I had never before photographed moving water at night. I loved the blurred water and the sense of movement it imparted to my images. I selected this image to process because I like the composition of the river's leading lines.
The raw image 14 mm, 25 seconds at ISO 3200
While the camera can see more light than I can with my naked eye because the aperture is open longer, there is still less color visible because the only illumination is moonlight. So as I opened the image in Adobe Bridge, I increased the exposure, color saturation and vibrance
Color enhanced & lighter exposure in Bridge
Once in Photoshop, the first thing I did was clone stamp out some unwanted elements, a streak in the sky from an airplane and a light from a camp on the other side of the river.
I am pretty obsessive about controlling the various elements of my image. I created layers that separated the foreground mountains and rocks from the river and also separated the stars from the sky and the foreground. These layers were isolated by using the Select/Color range tool and the Magic Wand tool to select the part of the image I wanted, then copy, create new layer and paste the item onto the new layer. This way, I have control over each element of the image. I do not delete the original, background layer.
So for example, use Select/Color range to select the whitest star in the image. Dial up the intensity until all the stars are selected. Command Copy. You will undoubtably also capture some unwanted foreground. Make a new layer. Name it “Stars”. Command Paste to paste the stars on the “Stars” layer. Use the Brightness/Contrast tool to brighten the layer to 100%. Use the eraser tool to erase any white foreground elements that you don’t want in the “Stars” layer. Because the stars are located in the sky and the foreground is not, this is the easiest way to have just stars in this layer. Keep this layer on top. You may want to desaturate all the color out of the “Stars” layer to make it whiter. Depends how much color you want in the Milky Way if that is in your shot.
Unprocessed sky with noise at 100% crop
I then selected the blue of the sky using the Select/Color range and the Magic Wand tool. I copied that, created a “Sky” layer and pasted the blue sky onto that. I adjusted the color in Image/Adjustments/Color Balance. Then applied a Noise reduction filter and Smart Blur filter to that layer. Be sure that the “Stars” layer remains on top. This separates the sky (pushes it further back) from the foreground and the stars, creating greater depth of field.
Sky post-processing at 100% crop.
The obvious change is that the color of the sky is much bluer, but if you look closely, there is far less grain in the blue of the sky and the stars are much brighter than the luminance noise. This helps separate the stars from the sky.
I also wanted to remove grain and smooth the river. It already had a creamy blur from the aperture being open for 30 seconds, but as you can see when viewing a 100% crop, it has a lot of noise. If you are just sharing this image on an iPhone, that noise wouldn't be visible. But if you want to make a large print, that noise has to go.
Grain in the river
Here is the river with Smart Blur applied. As you can see, it also has the effect of separating the water from the rocks.
Smart blur applied to the river
After all these effects were applied to each of the layers, I saved a .psd version of the image so I could come back and edit it more later if I wished. I then merged all the layers into a .Tiff file to preserve it in all it's detail and finally in a .jpg version to upload to the web. Here is the final. You may notice that the wide aperture (I shot the Rokinon 14mm wide open at f2.8) resulted in some coma and vignetting, but I think that actually adds to the look in a positive way by bringing your focus to the center of the image.
Print ready final version
If you compare it with the original below, you can see the effects of the processing. If you were to look at any part of it up close, you would see that the grain has been reduced and the elements of the photo are separated from each other by their relative blur or clarity. As you can see, the processing made it more vivid, clearer and beautiful. In this image and with the post processing, the camera has allowed us to see something we couldn't see in person with our eyes.
As the night progressed, the Milky Way appeared. Of course, without the moon, the foreground was lost. I used my headlamp to do some light painting. In this next image, I have not brightened the stars.
Next time I am in a situation like this, I think I will keep my tripod in one place so I can merge the lit foreground provided by the moonlight with the Milky Way that appears later.
I like how the river and the Milky Way converge. It gives me a feeling of floating down a river of stars.
Milky Way over the river
Back at camp, I couldn't resist one more shot. It tells the story of where we were and what we were doing.
The raft resting under the Milky Way
I love night photography, especially when it includes the Milky Way. It evokes such a magical feeling in me when I look at nightscapes. I hope this helps you create print-worthy images of your world at night.