Shots like this never fail to mesmerize and blow the minds off. It is often the case that seeing such amazing photographs fills us with an enthusiasm to capture the heavens above. But getting to know the starting cost of DSLRs takes out all that was pumped in. Isn’t it so? Yes, I know, it is.
But it is more important to get started and all that is required to get started with night sky photography is a smartphone with a decent camera and a tripod(optional). It does give good results and to get 30 percent of the desired results, post processing often helps.
Here is an example of what iPhone 7 can do.
These images were captured on iPhone 7 before sunrise on 11th September, 2020 using Milky Cam and post processed in Snapseed.
So, in this article, I will be discussing a few basic terms of astrophotography and how smartphones can give decent results.
Basics to be Learnt
The three most important factors for night sky photography are the Aperture, the Shutter Speed, and the ISO. These three terms can be best understood with the help of an analogy.
Suppose, there are two equal sized buckets which are to be filled with rain water but one bucket has a wider mouth than the other bucket. If the rain water flows into the buckets for 5 minutes, then which bucket will have more water? Obviously, the one which has the wider opening. Same is the case with the camera lens. The wider the lens is opened, the more light it gathers and the brighter the image is.
It can be understood by taking the term ‘exposure time’ into consideration. Suppose, you have two identical buckets into which the water has to be filled from two taps. One tap is kept open for 3 minutes and the other tap for 5 minutes. The term ‘Shutter Speed’ is analogous to how long the tap is open. Now, clearly, the bucket which had in flow of water for 5 minutes will have more water as compared to the other bucket. Similarly, the longer the time for which the camera lens is kept open (or exposed to light), the more light it gathers. And the amount of light entering is directly related to the brightness of the image.
The slower the camera shutter, the longer is the exposure time.
The ISO is the light sensitivity of the camera lens. Suppose, you cover the base of one bucket with a piece of cloth and the base of the other bucket with a sponge. Now, if 10 glasses of water is poured into each bucket, which bucket will absorb more water? The answer is clear- the bucket whose base has been covered with a sponge because the sponge is a better absorber than the cloth. In other words, the sensitivity of the sponge for water is more than that of the cloth. That is why it is capable of absorbing more water. So, if the camera ISO is higher then the light sensitivity of the lens is more and hence, even the dimmer sources of light can be captured.
But increasing the ISO results in a grainier image. This is due to the introduction of noise or disturbance. For this, let us take into account another analogy. Have you ever seen the game of shooting the balloons hung on a board? If yes, then suppose that there are 20 balloons on the board and only 6 bullets in the gun. Even if you shoot one balloon per bullet then you will be able to shoot just 6 balloons at maximum and 14 will still be left. Now, the balloons on the board are analogous to the pixels on the light sensor of the camera. The bullets hitting the balloons are analogous to the light photons hitting these pixels. And the balloons left are analogous to the noise is an image. Let us now see how these points relate to the night sky photography.
Night sky photography is a low light photography, since the stars are the distant point sources of light. So, even if more pixels are made available to gather light, not all of them are illuminated and these unilluminated pixels introduce noise to the image. This noise makes the image grainier. However, there are various other sources also that can introduce noise to the image.
Here is a comparison between two images of the same part of the sky- the first one has a higher ISO value than the other.
The reason why the first image has less number of stars despite a higher ISO is because of the exposure time. The exposure time for the first image was 30 seconds whereas for the second image it was 5 minutes. But as for a comparison, the first image has a considerable number of stars despite a short exposure time because of a higher ISO.
Another key term is FPS which stands for Frames per Second. As the term suggests, it refers to the number of shots that the camera can capture in a second. The higher the FPS value, the more detailed and smoother the image will be.
Now, let us take these key points to our backyard for a practical astrophotography session.
It should be noted that the use of a tripod makes the phone steady as it eliminates the shaking of our hands. This gives better results. However, a tripod is completely optional for beginners. Instead, the phone can be kept at a place, maybe on ground or against a wall, where it remains steady.
One, Two, Three. Shoot.
This section is divided into two parts- iPhone and Android. The reader can follow any set of settings and instructions, depending on their smartphone OS.
The older models of iPhone do not have a manual mode in camera wherein the above mentioned factors- aperture, shutter speed, and ISO can be adjusted. However, the latest models have some of the manual adjustment features.
Manual Mode Settings
- Since we are trying to capture the distant point sources, the focus should be set at maximum (i.e. infinity).
- While capturing the stars or the galaxy, make sure that the exposure time is not more than 5 minutes. This is because the sky seems to rotate by 1 degree every 4 minutes due to the Earth’s rotation. This can cause a star trailing effect.
- The ISO should be suitably adjusted according to the light conditions. If the location is a dark site then higher ISOs can give good results. But if it is a light polluted location then try to keep the ISO value low because skyglow can result in a poor quality image.
- If aperture settings are available then open the shutter to the widest. For instance, f/1.4 corresponds to a wider opening and as the number after the slash increases the shutter opening gets narrower (refer to the exposure triangle).
- If you are trying to capture the Moon then keep the ISO value extremely low and choose a narrow aperture. Likewise, the exposure time should also be not more than a minute.
Milky Cam Settings
The application that I recommend for iOS is Milky Cam. It is a free application available on the Appstore.
The app offers various camera setting sliders and buttons, some of which are listed below.
- Bright Slider: This slider can be used to increase or decrease the brightness of what is visible in the night sky before capturing the image. The higher the bright value, the more light is gathered and this makes stars appear brighter in the image. However, much higher bright values tend to distort the image by pixelation.
- Focus Slider: The focus can be adjusted on a scale of 0 to 10. For capturing the night sky, the slider should be kept at 10.
- ISO Slider: The ISO value is to be adjusted according to the location and sky conditions. Higher ISO values result in a noisy image.
- Rate Slider: With this slider you can adjust the FPS value between 3 and 5. FPS value 5 results in better quality images. All the frames captured are stacked one over the other to give the final image.
- Time Slider: This lets you choose the total exposure time which ranges between 1 to 60 minutes. The time should not be more than 5 minutes as the sky rotates 1 degree in every 4 minutes. The image is automatically saved after this time slot expires. 0 exposure time gives you unlimited exposure and you need to click the save button manually.
- Tripod: Select this mode if the phone is mounted on a tripod. This will result in a steady and better image. Do not select this mode while doing hand held photography as then the phone will not reduce the effect of vibration caused by the shaking of your hands.
- Skyglow: This mode reduces the skyglow which results in more stars that are visible in the image.
- Start: After you are done with the settings, click start to initiate capturing the image.
- Pause: This pauses the capture.
- Save: If you have chosen unlimited exposure time, then clicking this button completes the capturing process and saves the image to the phone’s gallery.
These are the major settings and buttons available in the application.
Now, before pressing the start button, make sure that you choose two stars in the night sky to align your image with. This is done by selecting any two stars on your screen. As you select a star, a green square encloses it.
If you are capturing the image in limited exposure time, then after your image is automatically saved, you get a few post processing options on your screen- Bright, Contrast and Paint. Increase the bright value to see more stars in your image. Increase the contrast for a better quality image. Once you are satisfied with the result, click on the save button again. You can repeat this procedure until you press the stop button available in the post processing options.
Most of the android phones have manual camera settings or the Pro Mode which allows you to adjust the aperture, shutter speed, and ISO.
Manual Mode Settings
The manual mode settings are the same as stated above for iPhone.
There are various applications available in the PlayStore which can help doing manual adjustments. One of those applications is Adobe Lightroom which is a free app. The manual setting options are the same as stated above. It gives decent results.
Post Processing is basically editing and adjusting the image to get desired results. Snapseed and Lightroom are the two well known apps which can help produce decent results after post processing. All you need to fine tune the image is adjusting the brightness, contrast and detailing. Sharpening the image to some extent gives better results. However, you can try anything with the image during post processing.
From fine tuning, to get better realistic images to merging two images to make something impossible like this, post processing helps.
A Homework Exercise
To make this learning even more interesting and fruitful is that you try what you have learned. Try capturing your favorite constellation. Try it with different settings. Be creative with post processing. And you are good to go!
References and Further Readings
“The Exposure Triangle.” Action Camera Blog, 27 Mar. 2019, actioncamera.blog/2017/02/22/the-exposure-triangle/.
Prower, Tony. “What Is the ‘Truth’ behind Noise and High ISO?” Iceland Photo Blog, Iceland Aurora Photo Tutorials, 13 Jan. 2020, www.icelandaurora.com/phototutorials/guide-to/camera-lens/what-is-the-truth-behind-noise-high-iso/.
“What Does Frames Per Second Mean?” Shutter Muse, 26 Mar. 2015, shuttermuse.com/glossary/frames-per-second/.