- Star trails, image credit: Ralph Clements
Star trail images are beautiful to look at and they are captivating because they make time visible. These images can be made either by exposing one single image over a very long period or by taking many shorter exposures and combine them afterwards. Digital cameras deliver images as electronic files, making combining very easy – particularly with software that does all the combining work automatically. One of these software tools is the program Startrails. This software has been developed by Achim Schaller, and he did an outstanding job. Not only is his software really easy to handle, but it comes with powerful features – and it is free. Startrails can be downloaded at Achim’s website.
Startrails is designed to automate star trail image processing by combining a series of input files into one final image. It is Microsoft Windows based and runs on Windows XP and later versions. Microsoft .NET framework has to be installed on the computer. Simplicity is a key attribute that sticks out immediately. Only 6 buttons maneuver through all functions of this software. It processes input files in JPEG, TIFF and BMP format and stores results also in these formats.
Processing Images with Startrails
Processing star trail images consist of the following steps:
Select all star trail images at your HD or memory card. It is recommended to go through every single image and unselect the ones that have flaws. Air traffic or blinding lights of a passing car can sometimes spoil a good series. Taking out one or two sequential images is virtually not noticeable in the final star trail image but improves the overall appearance considerably. Sometimes however, “disturbances” are wanted; the firework of a meteor or the bright reflection trail by the International Space Station (ISS) are usually considered an upgrade to most images.
Startrails software handles dark frames, or Darks for short. Darks are taken with the lid on the camera lens. This way only noise that is caused by the CCD chip is recorded. Noise in the actual images is random, but each CCD has a particular noise pattern which, can be subtracted from the final image pixels. This step improves the image quality significantly. If more than one Dark is available, Startrails averages them. Using Darks is highly recommended when images are taken with high ISO speeds.
Averaging images improves the signal to noise ratio. As a result it reduces (random) noise of the images and increases brightness (luminosity) of the stars. The averaged image becomes brighter and is blended into the resulting image.
No interaction is required during the run. After it finished, results can be saved in JPG, TIFF or BMP file format.
Note: Images can often be improved by post processing. Stars can be made brighter, background sky can be darkened. Good image processing software is available from many companies or organizations. Photoshop is probably the most common software for astrophotography, but freeware like GIMP performs also quite well.
Time Lapse Movies
Startrails has another powerful feature: it can create time lapse movies. Of course, it can create any kind of time lapse movies, not just astronomy movies. The output format is AVI with the following possible compressions:
Full Frames (uncompressed), Microsoft RLE, Microsoft Video1, Microsoft H.263 Video Codec, Microsoft H.261 Video Codec, Indeo® 5.10, Cinepack codec by Radius, Logitech Video (I420), Intel Indeo Video R3.2, Intel Indeo Video 4.5, Intel IYUV Codec.
Startrails converts the image input resolution during compilation into the wanted AVI screen size. The same is the case with the desired frame rate (fps) and some compression settings to set the streaming speed (kbps).
I’m often asked the question: What do I need to take star trail photos? Well, the answer is: not much. A camera with remote capability and a solid tripod is basically all that is needed. The camera should make JPEG, TIFF or BMP images. The tripod has to hold the camera steady, even when light wind gusts occur.
DLSR cameras are perfect, but simple point-and shoot cameras may work as well. Even smart phone cameras may be suited. There are no real strong demands on camera optics; it simply depends on what image quality level you desire. The better the optics the better the resulting images will be. The faster the lens (1/f) the less ISO speed is needed and with that, lesser noise is introduced. Other things to consider:
The memory card must offer sufficient space to hold the truly huge amount of data that will be stored during the shooting session.
Remote Control Capability
Some cameras offer image-series capability, these cameras can work on their own. Most other cameras need to be remote controlled. Whether continuous shooting mode is used or a remote control with multiple timer capability (intervalometer) is connected to the camera, depends on the preferences of the photographer. I prefer remote controls with timers because they give me most flexibility and I can choose any delay between two images. This allows setting longer intervals for time laps movies.
Wide Angle Lens
Star trail photos look better with many stars on the image. Foreground objects are improving visual image balance. Most photographers use their widest angle lens (or zoom setting) for these photos to capture as many stars as possible for best effects.
Most digital cameras have great difficulties focusing on stars when the rest of the image is extremely dark. Manual focus capability is required for star trail photography; any auto focus feature on camera or lens has to be off.
Startrails is a powerful, yet easy to use all-in-one program for star trail imaging. It allows to create time laps movies in AVI format. Startrails is great freeware and well suited for beginners and advanced amateur photographers.
Send us your star trail photos. Tell us where and how you made them.
Star Trails and Night Photography
Great website by Steven Christenson – highly recommended. Steven provides a wealth of information on star trail photography. His gallery shows breathtakingly beautiful star trail images.
Star Trail Photography
Harald Eden’s website offers also good information on star trail imaging. Additional information is provided on Lighting and Clouds photography.
- Constellation Orion - Image captured with Canon SX120 (10 exposures, 4 seconds each, ISO400)
Is is possible to make astro-images with entry level digital point-and-shoot cameras?
The answer to that question is a reluctant “somewhat”. With a basic camera it is indeed possible to shoot decent astro-images but the objects are rather limited: the moon and star constellations.
It is not about pixels
Basic astrophotography is not about Mega-pixels. Good images can be taken with cameras of 4 MP, or even less. What is important are three vital camera features, without them astrophotography will become a gamble. These features are:
- Manual focus
- Capability to preset exposure time (Tv)
- Capability to delay exposures.
Another component is of great importance: a solid tripod. The magic word here is “solid”.
Manual focus is important because of the way cameras perform auto focus. Some compare contrast changes. Sharp images have more pronounced contrast changes between adjacent pixels, unsharp images deliver more gradual changes. Other cameras compare bit patterns in specials sensors (phase detection). The patterns are shifted when the image is out of focus.
Either way, both methods are not really helpful when imaging a quasi black dark sky. Furthermore, if there is any contour visible in the image (f.e. a tree in the foreground), automatic focus will jump right at it, putting the actual celestial object out of focus. Astrophotography objects need to be focused manually to infinite.
Manual Time Setting (Tv)
- Moon – Image taken with Canon SX120, post-processed with GIMP
Time setting is important because the amount of light gathered by the CCD is only a tiny fragment compared to that of daylight images. This means, the exposure time need to be long. Typical exposure times for imaging stars are between 1 second and 30 seconds.
Tripod – Solid
A solid tripod will keep the exposing camera steady in position. With long exposure images, any vibration will be clearly visible in the images. The camera has to be absolutely still. For noise reduction purposes we need to take a series of at least 10 images, ideally 30-50. More on this subject later.
Even if the camera is firmly mounted on a tripod, pushing the exposure button will cause slight vibrations. The result is star streaks in the image. Exposure delay prevents this effects. Many cameras have a built in 2 seconds or 10 seconds delay. When the button is pushed, there are still initial vibrations, but the delay allows mount and camera to stabilize. The result will be significantly sharper images.
Zoom – Better Not
Some cameras have a zoom feature. Unless you are shooting the relatively bright moon with a very short exposure time – just forget the zoom feature of the camera. Why? Because the Earth rotates. This will show badly in the images in form of elongated stars. Please try to follow the short calculation below – it is indeed eyeopening.
The earth rotates once in 24hours, one rotation equals 360 degrees. That means, in one hour the rotation angle is 360/24=15 degrees, and in one minute it is 15/60 = 0.25 degrees, right? A quarter of a degree does not sound a lot.
True, but… Lets say we want to expose a the constellation Orion for 12 seconds. The angle the earth moves during this period is 0.25/5=0.05 degrees. A 10x zoom would increase the apparent angle by the same factor of 10. Within 12 seconds the image would shift by 0.5 degree.
One might think, that still seems negligible. Does it really have an effect? – Yes it does, and very much so. Picture the moon. The angle of the moon is, well, 0.5 degrees. That’s right, within 12 seconds exposure using 10x zoom, stars in our image would become as long as the diameter of the moon is; definitely not what we are looking for.
So, how are images with a high power telescopes possible?
Astrophotography with high power telescopes requires special mounts; they are called German Equatorial Mounts (GEM). These mounts have gear and electronically controlled motors that move the telescope exactly so that it perfectly compensates for the Earth’s rotation. You have probably guessed it: these mounts are rather expensive. Price depends on their carrying capability and accuracy. Entry level models that can be used for basic astrophotography start at about $500 ($300 used), and with growing demands, mounts can reach quickly true astronomical prices.
- Make sure the battery is fully charged and the memory card offers enough space.
- Reduce the brightness of the camera display to minimum. This helps to keep / maintain the night vision.
- Mount the camera on the tripod.
- Choose your object
- If possible set your camera to the highest ISO speed.
- Manually focus to infinity.
- Set exposure delay to 2 (or more) seconds.
- Set exposure time (Tv) to 5 sec.
- Take your first test shot. You can see if the object is framed right and the image is in focus.
- You might need to play with ISO speed and exposure time to optimize image exposure.
- Once done and you are satisfied, take a series of at least 10 images of your object (recommended 30-50).
Note: photos of stars look always quite dark in the camera monitor. It is often advised to increase the brightness of the image later during post processing.
Post processing (very basic):
This following description is for images with stars (not applicable for moon shots).
- Load your images to your computer and inspect every single image
- Sort out wiggly images, and such that have unwanted artifacts like plane or satellite trails
- Stack the remaining images with DeepSkyStacker (DSS) – setting: average
- Once DSS has created an image, optimize it with the build-in post processing tool
The advantage of stacking a series of astro-images (rather than using just one image), is that the noise portion will be significantly reduced, and the lunimance and saturation of the actual objects (stars) are emphasized. Since we are working usually with high ISO speeds, noise is much more present in astro-images than it is in daylight images.
- Catching the Light – Great site on Astrophotography with a DLSR by Jerry Lodriguss. Noise reduction in astronomy images
- Refractor 70mm on alt-azimuth mount
This article is for people who are in the market for their first telescope – but have only a very limited budget (say $100) at their disposal. Some amateur astronomers will say spending $100 on a telescope is wasted money, simply because there is no great telescope for that amount. Good optics is expensive, but not everyone has hundreds of dollars to spend and there are indeed some decent telescopes that are fun and do not break the bank. A tight budget should never prevent anyone to start a fascinating hobby.
Telescopes are available in three basic types: refractors, reflectors and catadioptrics and they come with different mounts. An Astronomy Source article “Introduction to Telescopes” in coming soon. The link from souledout.org provides also a nice overview on telescope types.
What can you see with a beginners telescope?
Quite a lot. I heard people complaining that the view through their basic telescope did not reveal bright and colorful images. Well, do not expect Hubble quality images with a $100 telescope. Suitable objects for these telescopes are the moon, the bright planets Jupiter and Saturn, some of the brighter deep space objects, and stars. Observe Andromeda Galaxy (M31) or Orion Nebula (M42), you can also see the famous Hercules Cluster (M13). Stars shine in different colors due to their different temperatures and consistence, and there are many exciting double or ever multiple star systems to watch. Did you know that Polaris, the North Star, is actually a 3-star system?
When looking for a budget telescope, keep in mind:
- Do not consider department store telescopes that come with a ton of accessories, parts and pieces, and promise magnifications of whopping 500x or even more. These items are usually toys. There is nothing wrong with toys, but really, don’t expect clear images or lasting fun and excitement with those. What you can expect is inferior optics a lot of plastic parts that will break soon.
- Glass lenses. Plastic lenses simply do not deliver the view quality of well polished and adjusted glass lenses.
New versus used
Telescopes can last very long if they are treated well. Used scopes are often available for half the price of a new one and many astronomers choose to buy used, simply because they want more: for the same money they get a much better (used) telescope, offering better images.
- Be very careful buying a telescope at a yard sale. You may get lucky and find the deal of the century. More likely is however that the item is in a bad shape, because it has been neglected over years.
- However, used equipment sold by serious amateur astronomers is usually in pretty good condition. True astronomers care about their equipment. A good source buying used telescopes and accessories is www.cloudynights.com. Check their classifieds and see what it offered here. Sellers describe their items in detail and provide usually very reliable information about the condition of their goods. Look for other dedicated astronomy sites that offer classifieds.
- If you decide to buy used, you should wait – and be quick. This sounds like a paradoxon, but you should watch the classifieds for a while to get a feeling about a fair market price of the the item you have in mind. When you see the right one, be quick to get it. Good items are often sold within a couple of hours.
Further items for amateur astronomers:
- Planisphere. Easy to operate map like device, that shows you where stars, constellations and planets are – all year long.
- Red Flashlight. Eyes adapt to the dark, this is called night vision. Night vision takes a while, about 15-30 minutes, but allows to see much more and much fainter objects in the dark. Exposure to bright light, with the exception of red, erases light vision immediately and it takes another 15-30 minutes.
- A good astronomy book about telescopes and star watching gives helpful hints for the beginner and advanced astronomer.
Beginning astronomy is the start of a great, very exciting and fun hobby. A simple 70mm or 80mm refractor on alt-azimuth mount is probably the best choice as starter telescope for around $100. These telescopes are very easy to set up and simple to operate – just point and see the universe.