Star Trails, conclusion

Since I did my first star trail experiment August 28-29, it has been moonless and mostly clear, so I have done seven more overnight sessions. I used all three of my DSLRs and two lenses, trying to determine settings that will work for me if I ever find a more interesting foreground I want to use rather than my neighbors' houses. As I said in that original post, "you can make this as simple or as complex as you want to."

The simple version is: Use your camera's built-in intervalometer to take 360 images with the widest lens you have. Suggested settings are 3600K color balance, maximum aperture (probably f/2.8 or f/4), ISO 400, 30-second exposures, high-quality jpg. Import them into the free StarStaX program and hit "Start Processing." Save the result. The more complicated work flow is shown at the end of this post below the images.

The first two images are from my second session and are still a couple of my better ones. I might redo the star trails image to remove some of the extraneous noise, such as the airplane track that cuts right through Polaris. The single frame is from about an hour into the three-hour shoot and shows a satellite flare and two partial airplane tracks. The frame was processed with a color balance of 3500K and lens profile correction. One lesson learned quickly is not to use lens profile correction in Lightroom when preparing hundreds of images to be stacked. A weird moire pattern can result. But for this single image, it is fine.

Color balance 3500K, with lens profile correction

The night of Sept. 4-5 was a disaster for star trails as passing clouds muddied up the composite image. But there were moments when it was clear, and I processed this single frame of the Milky Way. My next potential project is taking multiple images of the Milky Way and stacking/aligning them to bring out more detail. This is just a single 30-second image, which is about as long as you can go with a 14mm lens before the movement of the stars becomes evident. This frame was processed with a color balance of 3300K, which is probably a bit too cool.

To this point I was shooting with my 6D because it is the only DSLR I have with an intervalometer. The maximum exposure time is 30 seconds; anything longer and you have to use the bulb setting. The maximum image count is 99 or unlimited, so if I wanted to shoot 240 images I had to set it on unlimited and go out in the middle of the night to stop the camera. For the Sept. 5-6 session, I received my new intervalometer gadget so was able to switch from the 6D to the 5D and shoot longer exposures with the bulb setting. This is a composite of 3-minute images, ISO 100, over four hours. It doesn't take Photoshop as long to stack 80 images as it does 480 images. I didn't scrub this image for color balance (which was shot at 3300K) or airplane tracks, and there is a corner of the house showing at upper right. I set the intervalometer to shoot 120 images in six hours, but I negligently put an old battery in the camera and it died after four.

For the Sept. 6-7 session, I switched to the ancient 1D, which has a sensor crop of 1.3x. This means the 14mm lens only gives coverage of 18mm, less wide in other words. This composite needed to be cleaned up due to the car headlights shining right into the lens.

The final image shows the 1D again, this time with the 24-105mm zoom set on 24mm. With the 1.3x sensor crop, it is equivalent to 31mm. Settings were 261 images over 6.5 hours, 90-second exposures, ISO 400, color balance 3600K. I shot a dark frame and subtracted it from the composite, hopefully reducing some of the sensor noise. I pointed west toward Red Lodge Mountain, which gives a different pattern than aiming north toward Polaris. It was smoky overnight, and the trails near the horizon are fainter and oranger as a result.

Here is the workflow I have developed so far. It looks like a long list but is not that complicated. Just time consuming.

• Suggested settings for a Canon DSLR are RAW file format, ISO 200, 90-second exposures, 14mm lens, f/2.8, color temperature 3600K, at least 160 images over four hours. Set up and focus the camera when it is still light.
• Turn off the overnight lawn sprinklers.
• After it gets totally dark, put the lens cap on and shoot a dark frame. It would be better to shoot the dark frame at the end, but usually the session ends when I am asleep.
• Remove the lens cap, set the number of exposures on the intervalometer and start shooting.
• Go to bed.
• In the morning, retrieve the camera and turn the sprinklers back on.
• Import the images into Lightroom, including the dark frame.
• Select a random frame somewhere in the middle of the shoot, and click "D" to show the "Develop" screen. Adjust exposure, saturation and color balance. Make sure "Enable Profile Corrections" is UNCHECKED. Leaving this checked can cause moire patterns in the combined image. I saw this with the 6D, but I forgot to do it with the 1D and appear to have gotten away with it.
• Go back to the "Library" view. Right-click on the frame you just edited, scroll down to "Develop Settings," and choose "Copy Settings."
• Select all frames, including your dark frame, right-click, "Develop Settings," and "Paste Settings." Click on an image other than your source image and click "D" to make sure the settings got copied.
• At this point, I'm done with Lightroom and switch over to Photoshop.
• Select "File," "Scripts," "Image Processor." In section 1, select the folder containing the files just processed in Lightroom. Section 2, select an empty folder to contain the converted images. Section 3 select "Save as TIFF," no compression or resizing. Ignore Section 4 and run it. It will take a while to convert all the source files to TIFF files.
• This part can get tedious. Inspect all of the TIFF files for airplane trails, satellite flashes, car headlights and anything else you don't want in the final image. Loading batches of files into StarStaX can help find the frames that need to be edited. Going back into Lightroom and looking at the high-resolution previews also will help. Usually the "Remove" tool in Photoshop is your best bet for getting rid of this stuff. Overwrite the original TIFF with the edited version.
• Select "File," "Scripts," "Load Files into Stack." Select all of the TIFF files except for the dark frame.
• It will take a while to load all the files. In the Layers window, select all of the files and change the dropdown that says "Normal" to "Lighten." The star trails will magically appear.
• Select "Layer," "Flatten Image."
• Save the image with a unique name as a TIFF (Like "StarTrails07.tif") in the same folder as your other TIFFs and close it.
• Select "File," "Scripts," "Load Files into Stack." This time select your new file ("StarTrails07.tif") and your dark frame.
• Select only the dark frame in the Layers window. Change the dropdown from "Normal" to "Subtract."
• Select "Layer," "Flatten Image."
• Select "Filter," "Camera Raw Filter" and make any last-minute adjustments to exposure, saturation and color balance.
• Save the file as a TIFF, using a new name if you want.
• Crop the file to the desired dimensions (I use 1800x1200). You can sharpen now if you want, but I usually don't. Save as JPG and post to the internet.
• Eventually you are going to want to delete those hundreds of TIFF files. They take up eight times as much space as the original RAW files because they are uncompressed. But make sure you are done with them otherwise you will have to do all the tedious edits again.