Star Trails Photography
and the comparison of editing Software available
I was finally able to get back to taking photographs after a summer recovering from an injury and having loads of summer company. On my summer list I wanted to take some nighttime star images, both sharp star images and star trails images. To that end, I downloaded several very useful “apps” on my Ipad to help me determine where the moon’s phase would be and where it would rise and set according to my photographic locations.
The first app I downloaded was “The Photographer’s Ephmeris” (TPE), which is a fairly straight forward app, telling you the phase, time of rise and set of the sun and moon on a particular date. You are able to set a pin on your location which is determined by Google maps (internet, WiFi connection necessary).
After some more web reading, I downloaded a more detailed app called, “Photopill“. It is worth going online and following along with the tutorials provided for this app. Though I have only used the most rudimentary of settings with the app, I found that it gives me some very useful information not provided by TPE. For example, along the bottom scroll bar you can see where the sun or moon is along a continuum for the day you are photographing. This was especially useful to me when determining when the sky would begin to be at its darkest for the night.
Another app I downloaded was a very interesting app called “Dark Sky“. This lets you know if there is light pollution in the area where you will be photographing. I live in rural northern Vermont, but there are small towns nearby, so it was good to check to see if even those small towns would cause light interference during the nighttime shoot. Just an aside- when scrolling through this app, I was astonished to see that from Burlington, Vermont, up to Montreal and over to Ottawa, on Montreal’s western side, all the way to Quebec City, on Montreal’s eastern side, was completely polluted by light. This totals more than six hours of complete light pollution for this region. Even the rural eastern townships were not exempt. Astonishing!
After scouring these apps, I decided that the next photo date coming up would be the first new moon of September. As luck would have it, the sky for the two nights (the night of and the night after) of the new moon were clear and calm. I scouted out several locations ahead of time to decide which lens and location would be best.
I also decided I would try two different techniques. One technique would freeze the stars and the other would be for creating star trails. With both techniques it is best to get to your site around twilight and set up your camera and tripod. This way your will be able to see to focus your lens to the correct infinity point. If you are using a zoom lens, the infinity focus point can vary slightly across the range of the zoom. So, it is best to shoot when you can get your settings locked in. Also, as it gets progressively darker and you keep taking photos, one of these photos will probably serve as a base photo which you can use for layer blending with the night sky later in post-processing.
For the pinpointed, sharp star image, you must decide on the maximum shutter speed that you can use for each range of zoom to get the sharpest images. There is plenty of information online about the 500 rule, but I found this chart to be simplest and most helpful:
Focal Length (of lens) Full Frame Camera Crop sensor 1.5 Camera
10mm n/a 33 seconds
14mm 36 seconds 24 seconds
16mm 31 seconds 21 seconds
20mm 25 seconds 17 seconds
24mm 21 seconds 14 seconds
35mm 14 seconds 10 seconds
50mm 10 seconds 7 seconds
70mm 7 seconds 5 seconds
85mm 6 seconds 4 seconds
After setting infinity and choosing your shutter speed, you then determine your aperture. A good starting place is F/4 as this gives you some depth of field and gets you to the sharpest place for your lens (if the lens is 2.8mm) and it also lets in a reasonable amount of light. When all these settings are in place, put your camera and lens into manual mode as these will be your settings for the darkest part of the night. If you are taking images earlier in the night, only adjust the shutter speed or ISO to gain the correct exposure, making sure that f/4 and focusing on infinity are not touched. Also, in your camera’s menu turn on “High ISO noise reduction” and “Long Exposure Noise Reduction”. Any exposure over 3 seconds introduces extra noise into your image. Finally, set your white balance to “daylight” as you do not want your white balance shifting throughout the night.
Now to set your ISO. This depends on the quality of the camera you are using and what are its highest ISO noise capabilities. I was using an older Nikon D700 full frame camera. First make sure you are not set to “Auto-ISO”. After making sure that setting was correct, I started with ISO 1600 and, as the night progressed, was using ISO 6400. If I would not have exceeded the number of seconds for sharp stars for my focal length, I would have preferred to use ISO 3200 for this camera. Check online to find out what would be an acceptable amount of noise for your particular camera.
Below are some sample images from those two nights. Each image is a blend of the night sky with a foreground layer taken either earlier in the night. On the Clyde River images, I increased the ISO to gain more information in the foreground of the image. In post-processing I used Topaz Denoise and some High Pass sharpening of portions of the foreground elements. In the May Pond image, I did some exposure blending of a lighter foreground layer with the night sky layer. I was also working with Photoshop CS6 standard version.
On those same evenings, I also wanted to try creating some star trails images. The best star trails, the ones creating the circle like halo of stars, comes when you have a full northern view with the northern star, Polaris, as your anchor point. Often, however, the view you want does not align true north. Nevertheless, you can capture some interesting star trails.
To create star trails, it is best if you have a timed cable release called an Intervalometer. This lets you easily set the timed exposure for your images and well as the number of images you want to take within each set. I used the recommended settings from Harold Davis’ book, “Creative Night”. As he notes, you can set up your Intervalometer to take 100s of 30 second shots or you can set up the timer to take 15-20 four minute exposures. The former will give you less noise in the image and longer processing time. The latter will give you more noise but less processing time. Davis usually uses the latter, so that is what I went with as well. My settings for this image were: Nikon D700-Nikkor 24-70mm f/2.8 lens set at 24mm-Aperture F/4- ISO 200- White Balance, Daylight-Shutter Speed set to “Bulb” mode- the use of a Nikon MC-36 Intervalometer set for 15 exposures at four minutes each. I also shot one dark frame at the same exposure reading and created this dark frame by putting the lens cap on the lens and closing the viewfinder window. The dark frame was taken at the end of the photo shoot, before packing up.
Taking the photographs was the easy part. You just sit back and let the timer do its work. The surprise for me came in post-processing. I had intended to use Russell Brown’s Stack-o Matic script in Photoshop CS6. However, much to my dismay this function is only available in the CS6 extended version. What at shame, as I have no need for the other graphic related features of the extended version. So began my search for freeware that would create star trails. I came across several which all gave varying results. For all of them, I found it helpful to look for video tutorials on the web explaining their use.
DeepSkyStacker– Deep Sky Tracker is freeware software and there are some wonderful tutorials online by Doug German. This program seems to be best for Star Nebula and, as the name says, deep sky images. Also, as you look at Doug’s tutorials you will see that he advises using a program called GradientX Terminator that cost $49.95. Also with this program you need to shoot a specific number of dark frames and offset frames during the shoot, which I had not done. If I ever shoot deep sky images, this will be my go- to program.
Startrails– The advantage to this program is that it is very easy to use. Simply load the files and then load the dark file and let the program process the image. As you will see in the image below, the star trails are not as smooth as in other programs. Also the foreground of the stacked image had a sickly green/orange cast. Therefore, I used a foreground from earlier in the evening to blend in with the star trails image. (See application image comparisons below)
Star Trails Stacker– This is a script that you load into Photoshop (File/Scripts/star_trail_stacker…). You will have two choices, one as a layers files and one as a flat file. I used the flat file and just closed down each dialog box as it opened. This program as seen in the image below provides much smoother star trails. As with the Startrails program, the foreground in this image also had sickly green/orange cast. I used the same blending technique as with the Startrails program and used a foreground image from the earlier in the night.
Star Trails Action– This version of stacking star trails downloads as an action in Photoshop, which will then batch process your images (File/Automate/Batch). This is an action created by Chris Schur and he recommends creating a blank, black image the same size as the images you wish to stack. The black image can be created in Photoshop and does not have to be created during the nighttime photo shoot.
Comparing the images from each application:
Star Trails Images:
Perhaps it will depend on the images being used, but for these images, I would create yet a fourth image using the foreground and background in the Star Trails action, and then paint in the stars and orange mountain glow from Star Trails Stacker script. The Star Trails action also seems to create more star trails and a richer blue nighttime sky, so that will be my future first attempt when stacking stars. Then I will run the Star Trails Stacker script and compare. It might seem like a lot of work, but between the action and the script, Photoshop makes the stacking very easy.
So, in conclusion, no one software creates the perfect final image, but they are all free and give one a work-a-round if you don’t own Photoshop Extended.