THE NIGHT SKY - How to shoot Star Trails with North Star (Polaris)

My experience in making these images for someone who wants to start with astrophotography. 
Since my school days, I was always interested to see the night sky looking out for stars and moon. Being curious, i started reading about stars and different techniques of capturing these. I studied it myself by searching for numerous articles over the internet and eventually succeeded in getting some satisfying images. Many people have been asking me how did i achieve these images and what was the study and technique required to get such results!! Well, this is not just about taking photographs with known settings, but most of the activity happens as a part of post processing in the computer using multiple software. I would like to share my experience and learning for the someone who is interested to take such images.

Star trails occur because stars "move" across the sky as the Earth rotates, and so when a camera keeps its shutter open for an extended period of time, it will absorb this moving light as light trails. The circular pattern occurs due to the fact that the Earth rotates rather than slides across the universe.

Minimum Requirements:

• Camera: Preferably a DSLR. I would prefer a full frame camera.
• Manual Mode Functionality: “M” or manual camera mode means you can manually, and independently adjust the Aperture, ISO, and Exposure settings on the camera.
• RAW: Always shoot in RAW format. This is really helpful for your post processing.
• Tripod: A well made and sturdy tripod is very important for star trail photography.
• Camera Timer / Intervalometer: A timer is essential for star trail photography. It allows you to take multiple, long exposure photos, one after another. Most cameras only allow a 30 second maximum exposure time.
• Batteries: Make sure the batteries are fully charged as you will be shooting over a time ranging from 30 minutes to 3 hours or even more.
• Wide Angle Lens (Optional): A “fast” (number under the “f” is small ) lens is still recommended. The smaller the number under the “f”, the wider the aperture in your lens will open, allowing the most light to propagate through it in the least amount of time. In turn more light will hit your camera’s sensor, providing a higher quality image at night.
• A small chair, or a fold-able chair which would be easy to carry. This is required as you might have to wait hours together in the cold night
• If you are heading into a remote location it may be much colder at night than what you are used to where you live. So be prepared with some extra warm clothing and a strong stick for any animals approaching you 

Planning:

Before you get into the method of actual shooting, there are a few things you need to take care of first, namely - finding stars, and finding a clear sky. Try to be as away as possible from the city or you will end up with a lot of light pollution in your image which will blow the stars away. 

Some good application on mobile for atrophotography are as below:

1. LPM - Light Pollution Map to check the extent of light pollution near your city.
2. Stellarium Plus - This is a realistic sky map to observe stars, planets and constellations.
3. PhotoPills - This is the best app to plan the night photography, especially the star trail and milky way photography.

My first Star Trail shoot from my apartment terrace in Bangalore. I chose a New Moon night to shoot this image. Even with city lights, you can get the star trails and it all depends on how you understand your camera and the required composition. These images are an extract from about 330 images taken during a period of 2 hours. Processing the RAW images to JPEG took about 3 hours, after which I used a software called StarStaX to stack all these 330 images in my laptop which eventually created this image. There was a of light pollution from Bangalore city with clouds interrupting the shoot. Still managed to get these images. 

Captured with Nikon D7200, 18-140mm lens, 20sec exposure with fully manual settings.

This image was taken from my mobile phone on the cold night when my camera was programmed for star trail in Bangalore, Karnataka... You really need a sturdy tripod and avoid any type of camera shake.

Star trails from Gangtok - The image making process explained:

It was my dream trip to Gangtok. And I had made up my mind that I will not return to Bangalore unless I get a good Star Trail image which I was looking for!! And I was well prepared to face all extreme conditions, and of course had done all the required homework to make sure, things fall in place.

The photography gear which made this image:

Camera: Nikon D850 DSLR camera.

Lens: Tamron SP 15-30mm F-2.8 G2 ultra wide angle lens.

Tripod: Vanguard Alta Pro 2+ Tripod with Vanguard Alta BH-100 Ball Head.

Memory Card: Got a new 128GB memory card as D850 captures images of huge file size.

Head Light: Got a new LED head lamp flash light torch. Required to adjust lens and tripod in pitch dark conditions. 

Mobile Software: PhotoPills, Stellarium plus to locate constellations, North Star or Pole Star – also called as Polaris.

Laptop Software: ViewNX-i, Photoshop CS6, StarStaX, Adobe Lightroom. 

Field setup to achieve the above image:

Find the Polaris using the Stellarium Plus:
Polaris, commonly known as the North Star or Pole Star, is the brightest star in the constellation of Ursa Minor. It is very close to the north celestial pole, making it the current northern pole star. Polaris is famous for holding nearly still in our sky while the entire northern sky moves around it. That’s because it’s located nearly at the north celestial pole, the point around which the entire northern sky turns. So it is very important to find the Polaris, imagine the frame you are looking for with surrounding good subjects like mountains or any structures. In the above image, i had considered the Polaris to be towards right side and that made my picture more interesting to see the revolutions of other constellations. Below is the screenshot from the Stellarium Plus mobile app which i took while planning the composition of the image.

A screenshot of Polaris from Stellarium Plus App.

Setting the Tripod: 

This was a scary setup as there was a steep valley down the hill. So had to plan this setup with a lot of care and worst case disaster calculations, I had setup my tripod with one leg inside the balcony, and the other two legs of protruding outside the balcony where there was a one feet slab. This was necessary as I was shooting at 15mm which is a ultra wide angle and I had to adjust the tripod as the 15mm angle was so wide that the roof of the balcony was getting in the view finder. I had to get my view perfect to cover as much sky I could.

This was a scary setup as there was a steep valley down. So had to plan the setup with a lot of care and worst case disaster calculations, I had setup my tripod with one leg inside the balcony, and the other two legs of protruding outside the balcony where there was a one feet slab. This was necessary as I was shooting at 15mm which is a ultra wide angle and I had to adjust the tripod as the 15mm angle was so wide that the roof of the balcony was getting in the view finder. I had to get my view perfect to cover as much sky I could.

Image making in the D850: Nikon D850 DSLR is a high quality, professional grade 45.7 Megapixel Back-side Illuminated CMOS Sensor camera. Some features I found useful for astrophotography were:

• Tilt screen (for live view focusing and framing, and image review)
• Illuminated buttons which are necessary in pitch dark conditions. 
• High resolution of the sensor makes cropping images a good solution when imaging small objects
• Silent Live View Photography mode, commonly called the quiet mode or quiet shutter, that employs the camera’s electronic shutter to eliminate shutter sounds. 
• Shutter to close the View Finder which prevents any light entering the sensor. 
• The low digital noise, and useful extended ISO range yield excellent results for astrophotography (even with Noise Reduction settings set to OFF in the camera).
• Inbuilt intervelometer controls how often, how long and how many shots need to be taken. 

The exposure was for 20 seconds with at ISO-1250, and 5 sec interval for the next shot. Generally people go with extended exposure time, but I planned for less exposure time and low ISO because the lens had a wide aperture of f/2.8 and the dynamic range of Nikon D850 is great to get such images in the low light conditions. There were about 100 images which made this picture. Each image is about 55-60 MB in size. All shot in RAW format. It was about 6 GB of data to make One image of star trail. The shooting of images did go for nearly 1.15 hrs. Later the images were processed to JPEG format in View NX-i. I was super excited to see the trails but StarStax crashed all the time i tried to stack the images. Later i figured out, sine the image size of the individual JPEG images was huge, the Star Stax used to get crashed. So i found out a way to somehow stack all the images in Photoshop CS6. And further processed in Adobe Lightroom to extract most of the sky and colors. Everything happened in one night which included taking images and processing. By 5:00 hours in the morning, i had the first successful image of the Star Trail. Post processing plays plays a major role in making your picture and this comes with practice. You should try with all of these softwares and enhance the creativity in you.

I hope this helps understand the technique to achieve the Star Trails and also finding the Polaris (North Star). 
If you have any questions / feedback, you can always comment and i will be happy to respond.

Thank you,
Viraj Karekar.