This image is at Antero Reservoir in Colorado that I captured on June 20th, 2020. On the other side of the lake is the campground where there were several RVs and campfires.
I primarily went to this area to take my son out with his telescope because there are fairly dark skies in this area. My son has a 12″ diameter Dobsonian telescope which can show amazing things in the sky! We had a clear view of Jupiter (bright dot on the left) where we could easily see the rings and red spot of this planet. Saturn was amazing, too, and the rings were clearly seen. Then we saw several galaxies, star clusters, and the Ring Nebula
There was quite a bit of air glow in the sky (green streaks), which is charged air particles from solar radiation. I am not going to get into the details of what air glow is, but there is plenty of information on the Internet if you want to know more about it. While this adds to the challenges for seeing things in the telescope, it does have a pleasant affect in images.
Since my son and I went to this area primarily to look through his telescope, I had not planned anything exciting for photography. However, I did bring my gear and decided that it is always good to stay in practice, as well as experiment a little. Anyway, this “practice” image is the result I got from that night.
To get this image, I armed myself with my Nikon D850 that had a Sigma 35mm Art lens attached to it. I also brought a Tiffen Double Fog 3 filter (more on this later). For long exposure photography such as this image, it is a must to have the camera/lens mounted to a tripod because there are several seconds when the shutter is open and you will need the camera to be steady for a sharp image. I also brought a remote shutter release to minimize any vibrations that may occur from manually depressing the shutter button on the camera.
I turned my camera on for Live View (LCD screen on the back) to compose my image (how I want to the image to appear in the frame), and then made my adjustments for the desired exposure. After a few test exposures, I manually set my camera for shutter, aperture, and ISO ( 6 seconds, f/ 2.0, and ISO 6400).
I think here is now a good time to note about sharing exposure data (i.e. EXIF). Many times I am asked what exposure settings I used for the image. While this may be helpful as a baseline for someone to get started, it is never a, “one recipe fits all!” Unless you have the exact equipment I have, and are shooting in the same conditions, the exposure settings I share very rarely will look the same on your camera.
For the lens I used, the Sigma 35mm Art f/1.4, there are certain criteria ranges that I need to follow to get my desired image. This is a fast lens with a wide aperture at f/1.4. I rarely shoot starry night images with aperture wide open on this lens because there coma aberrations in the corners of the frame. Coma aberrations are an affect of certain optical designs due to imperfections in the lens that results in an off-axis point such as stars to appear distorted (have a tail like a comet). Some of the coma affects can be minimized by dialing the aperture down to let in less light (stopping down). This lens I used does have a fair amount of coma. For this image, I still wanted to let in enough light in, but also wanted to minimize the coma, too, so I chose an aperture of f/2.0. This was clearly not enough because the coma aberrations can be seen in the upper right and left corners of this image.
On a side note, the Sigma 35mm Art lens is great for portraits, or other dark scenes. However, I have found that this lens has not been the best to use for star images because of the coma problems. There are methods to remedy against the coma problem, such as taking a panoramic (frames to the left and right of the main image), and then crop out the coma areas. However, that is a lot of post-processing work. I normally use a Nikkor 14-24mm which is incredibly sharp, but the filter I wanted to experiment with only fit my 35mm.
The shutter speed is also important because you will need a long exposure to let in enough of the faint star light, but also minimize star trails. Star trails occur because you are on a fixed point on Earth, yet the planet is turning, so the stars appear as streaks. Depending on the lens that is used, there is a limit to how long a shutter is open before star trails start to occur. For the 35mm lens I used, 6 seconds worked the best to let in enough light and not have star trails.
Lastly for exposure, I chose an ISO of 6400. ISO is something you want to take in careful consideration. A high ISO can amplify a lot of light or signal coming in on the sensor, but that comes at an expense as noise (graininess). The amount of noise introduced by ISO depends on the size and quality of the camera’s sensor. My D850 handles high ISO well, but 6400 worked best as it amplified enough signal without introducing heavy noise that will need work in post.
When I capture starry night images, my preferred method is to take several frames and then stack them together. Stacking is a method that is very common in astro-photography and it is used to gain a greater exposure while reducing noise. Some people chose to use a tracker (a device that rotates at the same speed as the Earth), with a reduced ISO and greater exposure time, but that is more gear to bring and takes time to align to Polaris (the North Star). However, with my short shutter speed, stacking takes less time and achieves the same, or sometimes better, results.
Once I have collected my frames, I used the program called Sequator that stacks the images into a Tiff file which I can edit in a post-processing program such as Adobe’s LightRoom or Photoshop. For this image, I collected 10 frames, so it is the equivalent of a 60 second exposure. By the way, I only shoot in RAW format so as to keep all the image data.
I was also experimenting with the Tiffen Double Fog 3 filter. This filter has the affect of causing a glow around bright objects as if there was fog the light was shining through. I captured one frame with the filter on. By itself, the image is far to blurry on its own to be usable. However, when it is stacked with the previously stacked image, the brighter objects gain more glow while details are not lost.
Once I had the completely stacked image, I brought the file into Adobe Camera Raw and made minor adjustments for tone (light and dark), and white balance (color). I then opened the image into Photoshop where I used Topaz’s Denoise AI, and also did some minor curve adjustments for color ( a future blog article).
Anyway, I do hope the steps I listed above are helpful to similar images you may want to create. Please, feel free to comment on this post!
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