Previously we showed you some of the common errors of night photography and how to fix them, and specifically within that tutorial we talked about making star trails. Now that you’ve had some time to try and achieve the effect in-camera using a long exposure, we thought we would show you how you can fake it and make star trails with a lot less hassle.
Capturing the movement of the stars across the night sky would normally involve exposures of several minutes, but on a digital camera this can result in unwanted noise. The easiest way to overcome this problem is to take a sequence of shorter exposures (of around 30 seconds each) and combine them into a single image in Photoshop.
We’ve used 20 images in total, each taken using a 30-second long exposure. Combined, these shots can be used to create an image that looks like it was taken with an exposure of 15 minutes. There’s also an image where we’ve used a torch to ‘paint’ the foreground tree with light, and a ‘dark frame’, which you will use to reduce noise and dead pixels.
If this is your first attempt at combining images, try it with just the first five images to give you a feel for how the technique works, then you can move on to include more of the images as you get more confident with the processes involved.
The more images you include, the longer the star trails will be. Many experienced star trail photographers combine hundreds of images, but it can be extremely time-consuming to manually combine this many. In Photoshop CS3 and above you can open multiple files in a stack automatically, which will save time copying and pasting images. Unfortunately, this feature isn’t available in Photoshop Elements, which is what we’ve used for this Photoshop tutorial and is why we’ve chosen to combine images in batches of five.
How to make composite star trails in Photoshop Elements
Step 1: Import your images
Open your batch of start images. In the Elements Organiser, go to File>Get Photos and Videos>From Files and Folders. Ensure the image name is visible by going to View>Show File Names.
Step 2: Select your shots
With the images visible in the Organiser, select the first five images by holding down Shift and clicking on the first and fifth images. Release the Shift key, right-click on the images and select the Edit with Photoshop Elements Editor option.
Step 3: Copy…
Your first five images will now open in the main editing window. In our example, we click on the Startrails_002 tab at the top of the window to make that image active, then go to Select>Select All (Ctrl+A), and Edit>Copy (Ctrl+C) to copy the image.
Step 4: …and paste
Next we click on the Startrails_001.jpg tab and go to Edit>Paste (Ctrl+V) to place the second image as a layer on top of your first image in the Layers palette. Repeat for the other three images, so you end up with a stack of five.
Step 5: Change the Blending Mode
Now we close down the four images we’ve copied, leaving just the Startrails_001 image open. Select the top layer in the Layers palette and change the Blending Mode drop-down menu to Lighten. Do the same for all of the layers. You should now see that short star trails have appeared in the image.
Step 6: Flatten the layers
To simplify the process you can now go to Layer>Flatten Image, so that the layered image is reduced to a single layer in the Layers palette, complete with short star trails. Next, open the Organiser window again and select images 6 through to 10. Again, open them in Elements’ Edit window.
Step 7: And repeat…
Repeat the process described in steps 3 to 6, only this time we start with startrails_006.jpg and copy it onto Startrails_001, which we have already produced. Do this for all five images, and again change the Blending Mode of each layer to Lighten.
Step 8: And again!
Repeat step 7 for the remaining two batches of five images, until you’ve combined all 20 of the source images into a single image that shows the full arc of the star trails across the sky. Remember to flatten this image by selecting Layer>Flatten Image.
Step 9: Lighten up
To add the torch-lit tree, we open another start file named startrails_light.jpg and then Copy (Ctrl+C) and Paste (Ctrl+V) your main startrails image onto it. Change the Blending Mode to Lighten using the drop-down menu in the Layers palette.
Step 10: Reduce noise
Now we open our other start image, the dark_frame.jpg and copy and paste this image onto startrails_light.jpg too. This time, we change the Blending Mode of the dark frame layer to Difference. This reveals detail in the lower two layers, but reduces noise and ‘hot pixels’.
Step 11: View your image
Flatten the layers by going to Layer>Flatten Image. This will leave you with your basic star trails image. However, you will notice at this stage that as well as the star trails in the sky there is also a sequence of dots created by an aircraft.
Step 12: Zoom in
To see the unwanted dots more clearly, zoom in to 200% using the zoom tool at the bottom of the main window, then hold down the space bar and drag the image around until you can clearly see the first dot, around halfway down on the right.
Step 13: Cloning around
To remove the dots, grab the Clone Stamp tool and set a Radius of around 15 pixels. Set Opacity to 50%, then select a source point by holding down the Alt key and clicking on an area that matches the background around the area of the dot.
Step 14: Work carefully
Work around the image, cloning out each of the dots visible in the sky. You’ll need to take care when selecting a source point for the dots that pass close to the tree and the star trails. Make the tool’s Radius smaller for these areas if necessary.
Step 15: Crop your shot
Next you need to tighten up the composition to remove the ‘dead’ space at either side of the frame, and the dark foreground. Grab the Crop tool and select an area that removes these areas. Once you are happy with the new crop, press Return.
Step 16: Adjust the Levels
Create a Levels Adjustment Layer by clicking on the New Fill or Adjustment Layer icon in the Layers palette. In the Levels window, drag the middle slider slightly to the left to brighten the midtones, and the left-hand slider to the right to add more contrast.
Step 17: Fine-tune colour
To reduce the glow in the sky and the blue in some of the stars, create a Hue/Saturation Adjustment Layer. In the Hue/Saturation window, select Reds; drag the Saturation slider to -15. Then select Blues, this time reducing the saturation to -35.
Step 18: And finally…
Once you’re happy with your adjustments, flatten the layer for a final time by going to Layer>Flatten Image, and then save it. Make sure that you rename the image to prevent over-writing the original startrails_light.jpg image in the folder.