Guide to photograph Saturn and ISS transits – part 1 of a 2 part series
Have you seen our ISS-Saturn transit GIF? If you haven’t here’s the article we wrote:
And here’s the GIF again:
This is the first part of a 2 part series. We start with how to image planets, Sun and the Moon. The 2nd part of the series of this tutorial will teach you how to plan for an image the ISS transit itself. For general astronomy how-to, here’s a primer we wrote earlier: http://tinymos.com/how-to-start-astronomy-imaging/
How to image Planets, Sun and the Moon
Captured with the Tiny1 prototype
Imaging our celestial neighbors can be some of the most satisfying things in astronomy. They are close enough to show us great details and they are bright enough that they can be imaged from even the most light polluted cities, even Singapore. Currently there are several ways to capture these objects. We will cover how we did it with the Tiny1, followed by general recommendations and followed by the traditional capture methods.
Imaging with the Tiny1 camera:
A pure astronomy experience
At TinyMOS, we found that while we get professional results using the traditional methods, we thought there were too many processes involved. Tiny1 is designed to solve the complexities, to give users a pure viewing and capture experience.
Planetary imaging requires long focal lengths. We typically use lenses that are 300-500mm in true focal length. For the ISS Transit we used a 70-300mm lense we bought 2nd hand for 15USD. The more detailed image of Saturn was captured with a Samyang 500mm Mirror lens for 150USD. Adapter used was made by us. We recommend it as it comes with a tripod foot to prevent over stressing the lens mount on the camera body
For the Sun and the Moon, we are developing a 700mm equivalent focal length lens for fast and easy capture. The same lens captured the solar eclipse.
Point and shoot
Tiny1’s user interface is designed for ease of use. Just set the Tiny1 camera on a tripod and click search, enter the object you want to image for the night and it will guide you to the correct direction.
Here’s a user interface run through for the camera.
Go to the search menu by pressing the search icon.
Complete the prompt or type in the full name to begin searching
Follow the arrow prompt to find the object you are looking for.
With a bit of fine tuning, you will get the object in frame and begin capturing.
Auto capture preset gives you the correct settings for the object you are capturing. You could override it with manual settings or select the presets manually as well.
Just capture, upload to your phone and share it to your social media! Voila!
1. Avoid bright lights
Even though these objects are pretty bright, it is a good idea to avoid brightly lit locations (except the sun of course.) The reason to avoid brightly lit location is to prevent lens flares. Bright objects such as buildings, street lamps may be reflected within the optics of the lens. It causes false images and loss of contrast which adversely affects the image quality.
2. Avoid imaging across hot objects
Hot objects such as a road, an air-conditioning cooling tower or a building will cause turbulence to the air above it. If you look down a road on a hot day, you’ll see shimmering waves above it from the turbulence. This phenomenon prevents the camera from capturing a sharp image. Moving to another location where the planets are not seen through such turbulence would give much greater image quality.
Position of the object
The object that we are imaging, should be high above the horizon. If the object is close to the horizon, the light has to pass through more of the atmosphere on Earth. The atmosphere tends to move due to temperature fluctuations, creating the shimmering waves. It is especially prominent in cities with various heat producing fixtures such as air conditioning cooling towers, cars and even the roads itself. It’s best to wait until the object is 45 degrees or higher than the horizon to start imaging to avoid shooting through turbulent air.
Telescope or telephoto lens
As the astronomy objects are typically very small, it is recommended that a long focal length be employed to capture the images. A telescope of 2000mm focal length or greater is typically used, to provide more resolution and detail to image planets. A telescope or telephoto lens of 300mm focal length or greater is recommended for the Sun and the Moon.
*Important* The Sun require special care to prevent damage to the optics and the camera sensor itself, as well as your eyes. We use gel filters designed for solar viewing to capture our solar eclipse photographs. We often get questions if an ND10 filter is sufficient to capture image of the sun. We advice against this practice as the ND10 filter is not effective enough in reducing the amount of light from the sun. Besides, the solar film is much cheaper. Here’s a link to the filter we used and recommend: Thousand Oaks Optical Solar Filter
You may wish to stop here. The following is the guide for the advanced users:
Optional step: Tracking
Tracking allows you to keep the camera pointed at the same object for a longer amount of time. It may be good if the event would last a few hours such us the solar eclipse we captured.
Currently, we are using a Vixen Polarie as our star tracking mount. It is the smallest precise mount in the market at the moment. It is also easy to setup compared to a full sized telescope german equatorial mount.
Setup a sturdy tripod
- Preferably the base tripod head should be a geared head. It allows for much more control when calibrating. We are using a Manfrotto 410 Junior Gear head. It’s perfect for the job but it is very heavy. We’re looking to change to a Sunwayfoto DH-PRO. We have no experience with the latter and can’t comment on it apart from its lighter weight
- The tripod used should be as sturdy as possible. If using on soft ground, spikes are recommended. The tripod we are using is a Sirui T-2204X carbon fibre tripod. We had this tripod since Grey was a professional photographer previously. Any sturdy tripod would suffice
Level the spirit bubble level
Mount the Polarie and point it to North
- Make sure the switch is on the Northern Hemisphere mode. We used it in the Southern Hemisphere mode and pointed to North once. Took us 1 hour to realize our mistake!
Correct the angle for the lattitude
- Point the right ascension axis toward Polaris (Singapore is situated almost exactly on the equator, so our mounts are more or less perpendicular and we skip this step since we can’t see Polaris anyway
Turn on the tracking to the correct mode.
- Stars tracking mode for Planets. Lunar and Solar have their own mode selector switch
Mount and point the camera to the object at the widest zoom setting available
- Use the ball head below the camera, do not touch the tripod head below the Polarie except for tuning
- Remember to set focus to infinity first or the dim star light would not show up on the screen
- Zoom to the longest setting on the lens
- Focus again, either by the Tiny1 quality indicator or using a Bahtinov Mask
Note on Tiny1 Nikon to C mount adaptor
Note that it has its own tripod foot to prevent over stressing the C mount on the Tiny1 camera. The rear of the mount is a free rotating mount to allow easy framing of the subject being photographed.
The lens pictured and used for the ISS Saturn transit is a 70-300mm which we found in our last Japan trip for about 15USD.
Getting best focus
Traditionally a Bahtinov Mask (click for video tutorial) is the best way to ensure focus. We found it clunky and we don’t always have one at the correct size. With the Tiny1, the Bahtinov mask is no longer required. Simply turn the focus to infinity and use the focus quality guide on the Tiny1 to determine the best focus possible. Note that it will never reach 100% quality due to atmospheric effects.
Tiny1 for professional imaging
Tiny1 is designed for high speed capture. We are still in the progress of testing but it should achieve 60 fps of RAW capture at 2.5k resolution. The camera can implement some degree of lucky shot imaging and stacking to improve image quality. For professional results, download it to your PC or Mac to do the post processing. We will be releasing software to simplify image processing shortly after the launch.
For now, we can achieve this level of quality for Saturn with the above setup using a 500mm Samyang Mirror Lens.
Traditional imaging methods:
Hardware setup and capture
Traditionally the best way to image the Sun, Moon and Planets, is to use a web camera. These are scientific web cameras which are often connected to a laptop. Typical chip size for planetary image is 1/3″ diagonal to get the most angular resolution and reduce the waste of memory storage and increase capture frame rates. Typical chip size for solar and lunar imaging range from 1/3″ to 1″ diagonal.
To setup a telescope is quite a complex task, which is a post by itself. Instead of doing that, here’s a good go to guide to understand how to setup a telescope on an Equatorial mount for astronomy imaging: www.astro-baby.com
After setting up the telescope, the camera is attached to the rear of the telescope and linked to a laptop via USB cable and capture begins after the correct focus and exposure is determined. A free and excellent capture software used by enthusiast and professionals is the FireCapture software: http://www.firecapture.de/
Focusing the telescope is paramount to getting great image quality. A great way to get perfect focus for the planets is to use a Bahtinov Mask. Here’s a quick video guide on how to use one: https://www.youtube.com/watch?v=aMdkXrkygDk
Lucking imaging and post processing
The images are captured at the highest frame rates possible into a video stream. High frame rates are necessary for a few reasons.
1. Overcoming atmospheric distortion via lucky shot imaging.
Atmospheric distortion refers to the shimmer you see when looking down a hot road in the day. The fluctuation in temperature and density of the air causes distortion in the image. It is the same reason why stars twinkle at night. High frame rates allows you to capture the moment of calmness in the atmosphere when the image is less distorted. By running the image through a software, we can determine which are the images with the least distortion and select the frames for final use. This process is known as lucky imaging and was first developed by David L. Fried in the 1970s. Here’s a brief explanation of how it works and how it is improving the resolution of the Palomar 5.1M telescope.
2. Reduce noise
Having more frames allows different data point that can be averaged to reduce noise. Simply put, if we average enough good quality frames, noise information which are mostly random, will get averaged out. It results in a much cleaner looking image.
3. Rotation of planets
Planets, Jupiter in particular, rotates at high speed. In order to benefit from the above mentioned improvements, more frames are required. However if imaging duration is too long to capture enough frames, the details on the planet will get smeared out as it rotates.
Lucky imaging and stacking can be done via free software such as Autostakkert.