Astrophotography

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You would be surprised to know that a telescopedoes not let us see the night sky in all its glory. Everything is black and white to the eye.
Using a telescope to look closely at stars and planets has its charms, but you would be sorely disappointed if you tried to compare it with pictures off the internet.
On the other hand, a photo lets us see how colorful and dazzling the night sky can be. You can take pictures in various ways, from a simple smartphone on tripod, professional telescopes to other dedicated equipments.

Difference between astrophotography and normal photography

• The fact is, you are trying to photograph something you cannot see. The human eye cannot distinguish the colors given how dark it is. The vibrant colors of the night sky could surprise you.
  Astrophotography does not strive to resemble what is visible to the naked eye.
  You have never seen the glamorous details of the night sky with your eyes. There is an overarching idea about it, but no set standard.
• The night sky is extremely dark.
  There must be a certain level of light to distinguish between objects.
  It depends on various conditions. You can capture the Orion Nebula beautifully with a 400mm lens, which is larger than say, the 10x zoom of a smartphone.
  At F4.0, ISO 1600, light must be captured for at least 30 seconds for things to be visible.
  Taking atmospheric conditions into account, astrophotographers usually photograph the same object over an hour, portraying it in much detail.
• The earth is subject to rotation.
  Thanks to the earth’s rotation, the stars start to look like sticks instead of dots after more than 10 seconds of exposure on a 50mm lens. Accordingly, you have to use a separate tracking device for long-exposure photos.

• Post-Processing process is crucial.

Astrophotography is half post-processing.
It is rare to get a shot and be done with it, even if you use dedicated equipment.
Assume you get enough light in a photo against atmospheric conditions like wind, humidity, temperature, particulate matter, etc. But this will only apply to photographs where it is difficult to perceive details, like the stripes of Jupiter, etc.
Therefore, synthesizing multiple photos to reduce noise and increase detail is of the essence.
Also, if you shoot landscapes, you need to take the sky and the landscape apart and blend them later. You need to keep in mind that the landscape does not move, but the stars and the planets do.
If you stack it up as it is, either the landscape or the stars will be blurred in the photo.

The first photo above is of a star in movement, taken with long exposure. The other two have been taken five minutes apart.
The stars move faster than you think. Considering that, you need to separate the foreground (landscape) and the background (the sky) in long exposure astrophotography, to get a clear picture of both.

• The subjective intention of the photographer interferes a lot with the final photo.

Above are photos of the North American Nebula on Wikipedia.  The two show completely different colors.
If you search for images, you will see that, unlike ordinary photographs, in astrophotography, the same subject is processed in a wide variety of colors.
The shooting conditions may differ from normal photography, such as in infrared photography, etc. But in absence of a singular correct answer, the editing may be tinged quite a bit with the subjective intentions of the artist.

The conventional method of capturing celestial bodies using Galaxy

You can use Night Mode, Pro Mode, and Expert Raw for astrophotography on Galaxy smartphones.

Night mode

First, there is the night mode. Night mode has the advantage of easy setup and capture compared to Pro Mode and Expert Raw.

1. Open the Camera app.
2. Tap ‘More’, then select ‘Night’.
3. Select the time in the lower right corner and set it to the maximum.
4. Press the Shutter button.
5. You may shoot without a tripod. Hold the phone securely to avoid too much shaking.

Pro Mode and Expert Raw

You can also use Pro mode and Expert Raw in basic mode for astrophotography.
The configuration is complicated, but you can adjust it however you want.
The method of filming is almost identical in Pro Mode and Expert RAW.
The Expert Raw app can be downloaded from the Galaxy Store.

1. Secure the smartphone to the tripod.
2. Open the Expert Raw app or enter Pro mode in the Camera app.
3. Select one out of the UW, W, T, & ST cameras and place it in a shooting position.
4. It may be out of focus because of the dark. You need to set the focus manually in this case.
5. Configure the speed and ISO manually.
   If the sky is dark enough, fix the speed as shown below.
   Speed: UW - 30 seconds. W - 20 seconds. T - 15 seconds. ST - 4 seconds.
6. Configure the ISO.
   The ISO varies depending on things like the brightness of the sky on a specific day, the shooting location, etc.
   First, let's shoot with 800. If it comes out dark, go with a bigger number. If it is too bright, choose a smaller number. Adjust the number in this way.
7. You can set the color temperature to ‘Automatic’. You can also set it to whatever you want. It is recommended to set it to 3500K-4000K for manual setup.

Astrophotography mode

Expert Raw makes it easy for astro-photographers by supporting the astrophotography mode. It also provides a framing guide to make it easier.

The following processes are used for astrophotography usually:

Search ‘Astrophotography’ - Composition Settings - Camera Settings - Continuous Shooting – Combine/Synthesize - Post-Correction

Without specialized knowledge and experience, it could prove difficult to take photos of celestial bodies.
Normally, you can get a good shot in Pro mode by setting ISO 800-1600 for 20 seconds in a wide camera. But, it also depends on the shooting environment.
The camera takes dozens or more photos and synthesizes them  for several hours, for the sake of a good quality photo.

Astrophotography mode automates all of this, reducing it to a single touch.
It employs a lot of techniques to make complex astrophotography easy.
A tripod is also helpful for people without any prior knowledge or experience in astrophotography.

Image Stacking is
a technique that captures multiple shots of the same scene and synthesizes them to obtain sufficient light and detail.
Multiple frames with relatively short exposure are taken to get enough light and avoid motion blur for the stars in the background. This creates the effect of long exposure.
Image stacking is a great way to reduce noise and acquire extraordinary detail.

Photo quality improves greatly by simply taking several shots full of noise and lack of detail, and then synthesizing them.
In the astrophotography mode of Expert Raw, multiple frames are shot within a certain set time and those photos are automatically combined to create one file. The blurry stars (because they move with time) are also aligned.
For example, if you shoot with a wide-angle camera for 4 minutes, it takes 12 shots within an exposure time of 20 seconds.

1, 5, and 50 shots are stacked from left to right. The photos at the bottom are an enlarged display of the area highlighted in yellow. There is significantly less noise and heightened detail with the stacking of more shots.

• HDR

It is quite difficult to capture the night sky and bright landscape on the ground together in a frame. HDR is applied to control the saturation of bright areas in a landscape.

• Sky Segmentation

As explained earlier, the stars are in motion during the long exposure, so if you synthesize images in line with the stars, the resulting photo will have a rotational blur. To prevent this, the sky and the landscape are separated for both to come out clearly.

• Noise removal

Astronomical bodies in the night sky include stars that are not very bright. Excessive noise removal can erase stars like these. The way of processing photographs like these, vary widely depending on the photographer’s orientation.

We kept the noise removal to a minimum as bright or dark, we prefer natural-looking stars.

• Post-Correction

The purpose of the astrophotography mode is to show the sky and stars in their natural colors.
Post-correction ensures that saturation and brightness are adjusted to appropriate levels according to the concept of the photo.

Astrophotography

Astrophotography is a mode available in the Expert Raw app. Download the Expert Raw app from the Galaxy Store.
Launch the Expert Raw app and tap the gear icon in the upper left corner to enter ‘Settings’.
Activate the ‘special photo options’ to access the astrophotography mode as shown on the left below.
After that, tap the top-right icon to turn on the astrophotography mode as shown in the picture on the right.

The default shooting time is four minutes which can be adjusted up to ten.
The longer the shooting time, the less the noise and the more details.

 A lot can alter in astrophotography depending on the subjective view and taste of the photographer. Expert Raw's astrophotography mode seeks to eliminate the effects of AI as much as possible. It maximizes the performance of the hardware embedded in the Samsung smartphone camera to express the natural hue of the sky and numerous stars.

Astro Tracker

It is quite a task to tell which area you are capturing just by looking at a preview of the dark sky. This mode enables you to track constellations.
It provides minimal and non-complicated information for reference while shooting.

• Accuracy Calibration

Accuracy calibration may have errors because it uses GPS, geomagnetism, acceleration sensors, etc. like the conventional constellation tracker apps. But if you fix the tripod and wait a few seconds, a technique called ‘plate solving’ places the tracker in the same position as you see in the preview, enabling you to predict the result.

The following pictures have been taken in Korea with just a tripod and the astrophotography mode. The results are without any post-correction.

There are still limitations in capturing deep-space objects (nebula cluster galaxies). But with gradual improvements in performance, it will be able to photograph more nebula galaxies.

You can use your Galaxy in different ways to do astrophotography. Each way has its pros and cons, so you have to choose wisely according to the scenario at hand.
In terms of photo quality, it is best to shoot in astrophotography mode

It is hard to notice in the above photo given how small it is, but the astrophotography mode shows a lot of stars with long exposure, and the HDR makes sure the glimmer of the stars is unsaturated.

Photography by Astrophotographers

Let's take a look at a situation where astrophotographers go out to shoot with telescopes.

1. Loading and moving

It is difficult to get a good shot unless the sky is dark and free of light pollution from artificial lights.

Since you must carry heavy equipment, it is extremely rare to find a quiet place that can be accessed by a vehicle.
In my experience, you need to be about 50 kilometers away from the city center to get a good view of the sky.
So after disassembling a telescope made up of dozens of combinations of parts, you have to load a lot of luggage into the car before setting off to get the kind of photos you want.

1. Equipment installation and different types of settings

You get the following telescope upon assembling the parts on the site.

The picture above is the setting for observation. Setting up to shoot is much more complicated and time-consuming because you have a lot of equipment, such as wires, batteries, computers, cameras, etc. After installation, there are many processes to go through such as horizontal, polar axis, optical axis, guide test, etc. I will not explain these in detail.

1. Locating Target

You locate the object you want and place it within the camera frame. The target is tracked automatically by the computer.

1. Shooting

You configure the whole process of how many photos to shoot, and in what setting and start shooting. All subsequent processes are controlled by the computer.
There are several kinds of software to help with this, like NINA, KSTARS, etc.

1. Waiting

It may be as short as an hour or as long as till sunrise. You need to check on the equipment every once in a while to make sure the process is moving smoothly. Then, it is time to take a break the next day.

1. Post Production

All the files are sent to the computer and the post-processing starts.
The post-production work can be divided into the image stacking process and the post-correction process of fixing the tone and noise.

1. After working a total of two days from shooting to post-production, you get at most three photos.

Astrophotography is arduous, but at the same time, it is a wonderful story created by lovers of the stars.

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References

[1] ref. https://en.wikipedia.org/wiki/North_America_Nebula (captured by Wesley Chang. CC BY-SA 4.0) ref. https://ko.wikipedia.org/wiki/ captured by Oliver Stein. CC BY-SA 3.0)

[2] Astrophotography mode is currently available in beta. There may be unexpected errors. We are constantly improving it for good picture quality and usability.

[3] Astrophotography mode is not suitable for urban environments where stars are not visible to the naked eye. Long exposures of at least 5 seconds and ISO 200 or higher are taken, so We won't be able to take the photos We want unless We're in a dark sky where the naked eye can see at least 10 stars.

A photo that is too bright is taken and is missing during compositing, or the bright result is output as it is.

[4] In astrophotography mode, we can use a tripod to take the desired photos.

[5] Plate solving: A technique that analyses the distribution of astronomical bodies taken in photographs to find out exactly what the objects are and where they are headed.