discover the universe
Wednesday October 18th 2017

‘Star trails’

Astrophotography – Without a Telescope

Milky Way, Credit: Ralph Clements

By Ralph O. Clements

When I was invited to write about this subject for Astronomysource.com, I must say I was flattered and a bit flabbergasted too, as I do not consider myself an expert on the subject, nor a writer by any means, but just a guy who likes to go out at night and take pictures of the sky. I stumbled into this hobby when my wife brought home an old 4” Meade reflector telescope with a manual equatorial mount from a yard sale that she paid $60 for.

I took that thing out in the country and set it up (completely wrong, I now understand) and as darkness approached, held my point-and-shoot camera up to the eyepiece and took a picture of Venus. Well, now that was very interesting…it was certainly not a very good photo and I have learned it is hard to get a good one of Venus, but I could tell it was not a star, it was not round but had a semi-circular shape. Wow! I took a picture of another planet! That got the gears turning in my head and I just had to do more….I mean who would think I could take a picture of another planet, with a point-n-shoot camera and an old yard sale telescope?

“Camera Only” Images

I do take images with newer telescopes and a decent equatorial mount which I have acquired since. Imaging galaxies and nebulae is an ongoing goal and interest, but I have learned that it is time consuming, tedious and has a fairly steep learning curve. My view of the sky at home is very limited. So for the time it takes to drive out to the country and get all that gear set up and working, I am limited to weekends and then only weekends when the sky is clear. Since clarity of skies does not always happen on Friday or Saturday night, I often image without the telescopes at all. All the tips and advice offered here is just what I have learned and I expect others may have better ways of doing things.

Equipment

My research indicated that Canon cameras are preferred for astrophotography and the T1i is what I use for everything. I also have an older Nikon DLSR with two lenses, a 180mm fixed focal length and a 75-300mm zoom, for which I bought a Canon adaptor, but the 18-55mm “kit lens” that came with the Canon is what I use most often.

If you read up on astronomy and astrophotography equipment you will note it is often said that the mount is every bit as important as the telescope. My camera tripod is my mount and I fully agree that a sturdy tripod is a must. I am fortunate to use a tall Berlebach tripod with hardwood legs. The cheap aluminum department store tripods are not stable enough.

Figure 1: Orion at Peaks of Otter, Credit: Ralph Clements

Widefield & Star Trails

Camera only astrophotos with a static tripod fall into these three general categories:

Widefield – Single Shot

These include what would be considered “scenic” or “landscapes” in daytime photography, that is, including some portion of the Earth, as well as constellations and shot of the Moon (See Figure 1). I try to shoot as long as possible without having oblong or streaked stars. A high ISO setting helps with this and I often use 3200 ISO unless it is twilight or too much man made light is around. Figure 1, Orion and the Peaks of Otter, is a 10 second exposure and the stars are a bit oblong but not too bad.

Widefield – Stacked Images

Images that are composed of multiple single exposures, stacked and aligned in the computer to reveal much more of the faint light features than what is visible to the naked eye. Sagittarius (Figure 2) was taken as series of short, 6 second shots and stacked in the computer using Deep Sky Stacker. The exposure time for shot like this can vary depending on the target, its location in the sky and ambient light conditions. I find that targets nearer the poles may allow a little longer exposure than those on or near the celestial equator, which appear to move more due to their location.

Figure 2: Sagittarius, Credit: Ralph Clements

Star Trails Shots

Long Exposures or combined multiple exposures that show the apparent rotation of the stars above the Earth. Of course, the stars just appear to rotate because we are riding on the Earth which is really doing the rotating (Figure 3).

Taking star trails images is fun, easy and I like the look of them. Although a star trails image of say 40 minutes can be done on the “bulb” setting with a single exposure, this requires a remote timer and more importantly, a very, very dark site as the least ambient light will over expose the shot during that time. So I just take a series of 30 second shots and combine them using “Startrails” software, another useful and free program. This software is definitely easy to use and produces good results, although I do not notice much improvement when I use dark frames with it. For noise reduction I use “Noiseware Community Edition” in the final images instead. I recently became aware of another free software to do this, “Starstax”, and will be trying it soon as it offers more features.

On these star trails shots, sometimes it is good to have some moonlight on the subject and I will go out under a quarter to half moon and shoot them. I find a full moon makes it too much like daylight for my taste and if I lower the ISO under a full moon the stars don’t show up much. So depending on the amount of moonlight, artificial light and desire ground detail, I take these star trails shots at ISO setting of 800, 1600 or 3200. Generally, I try to get 40 to 60 minutes total exposure. Less than that and the trails are too short, more than that and chances are airplane will mess it up.

Figure 3: Startrails, Credit: Ralph Clements

Foreground and Framing

I try to pick a good site with some interesting foreground , although “fore-ground” in this case doesn’t mean close to the camera, rather, it means the part of the Earth that is shown.  I try to frame the shots so that the sky covers roughly ¾ of the frame, since the sky is the real subject and the foreground is really just a reference or point of interest.

Focusing

To get crisp focus on the stars and the ground, anything in the image needs to be as far away as your camera’s “infinity” focus distance, which varies with the lens. So I try to take scenes that I would focus to infinity on if I were shooting them in daylight, such as the farm you see in Figure 3.  For all my images I use the camera’s “live view “. This feature lets me zoom in on a bright star, or the moon and focus. If your target is too dim, aim at a brighter one or an artificial light a long way off and focus on it and re-aim at your target. Make sure your camera is not set to “auto-focus”, use “manual”. The Nikon I was using did not have “live view” but I used the same method, only I looked through the view finder at a bright star or light. Sometimes a few test shots were needed to get it right.   

Getting Started

As for general advice for other beginners, I offer the following

  • Read your camera’s instructions, particularly the section on manual control.
  • Learn to work your camera’s controls in the dark, the corollary of which is….
  • Don’t be afraid to experiment. I use the trial and error method, with lots of trial and plenty of errors. That’s okay though as I am having fun and try to learn from my mistakes, and I don’t have to buy film for a digital camera, so I don’t mind deleting the ones that didn’t come out. 

….just do it! Have fun with it.

 

Further Reading

 

Submit to redditShare on MyspaceSubmit to StumbleUponDigg This

Startrails – Software

Star trails, image credit: Ralph Clements
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.  

The Program

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:
  • Selecting images
    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.
  • Dark frames
    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
    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.
  • Run process
    No interaction is required during the run. After it finished, results can be saved in JPG, TIFF or BMP file format.

Startrails Software by Achim Schaller

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).
 

Equipment

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.

Camera

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:
 
  • Memory Size
    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.
  • Manual Focus
    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.

Conclusion

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.

 Further Reading

  • 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.
  • Astrophotography for $100
    Another Astronomy Source article that offers tips on astro-imaging with basic cameras.

 

Submit to redditShare on MyspaceSubmit to StumbleUponDigg This

Astro-Imaging for $100

Astrophotography on a Budget - Orion Image captured with Canon SX120 (10 exposures, 4 seconds each, ISO400)
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

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
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.

Exposure Delay

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.  

First Photos

Preparations:

  • 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.

 Shooting:

  • 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.  

Further reading

  • Catching the Light – Great site on Astrophotography with a DLSR by Jerry Lodriguss. Noise reduction in astronomy images

Coming soon:

  • Deep Sky Stacker tutorial
  • GIMP tutorial
Submit to redditShare on MyspaceSubmit to StumbleUponDigg This

A Telescope for under $100

Refractor 70mm on alt-azimuth mount
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.

Conclusion

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.   

 Further reading


  

 

Submit to redditShare on MyspaceSubmit to StumbleUponDigg This

Helio Now

Solar Dynamics Observatory

Solar Dynamics Observatory 2017-10-18T12:48:34Z
Observatory: SDO
Instrument: AIA
Detector: AIA
Measurement: 171

Latest Topics

The Moons of the Solar System

The Moons of the Solar System

More Questions Than Answers Think of our solar system, and for most of us the first thing to come to mind would be the [Read More]

Asteroid Mining

Asteroid Mining

Near Earth Asteroid Itokawa. A likely candidate for future mining opportunities. Credit JAXA Look back in history and [Read More]

Science@Home Wall of Fame

Science@Home Wall of Fame

People all over the world donate idle CPU and GPU time of their computers to support important scientific projects. An [Read More]

Top 10 Night Sky Objects for Astronomy Beginners

Top 10 Night Sky Objects for Astronomy Beginners

Your first telescope has just arrived and now you can’t wait to try it out. Trust me, I remember this feeling very [Read More]

Positions of Planets

Positions of Planets

The tables offer monthly positions of the four brightest planets: Venus, Mars, Jupiter and Saturn. Note, that a [Read More]

Observing Tips for Beginners

Observing Tips for Beginners

  Amateur astronomers have to face some challenges with equipment, weather and environment during their [Read More]

Astrophotography – Without a Telescope

Astrophotography – Without a Telescope

By Ralph O. Clements When I was invited to write about this subject for Astronomysource.com, I must say I was flattered [Read More]

Voyager Explores Stagnation Region

Voyager Explores Stagnation Region

 NASA’s Voyager 1 has entered a new region between our solar system and interstellar space, which scientists are [Read More]

Startrails – Software

Startrails – Software

Star trails, image credit: Ralph Clements Star trail images are beautiful to look at and they are captivating because [Read More]

German Equatorial Mount – Part 2

German Equatorial Mount – Part 2

The first part of this article gave an introduction of German Equatorial Mounts (GEMs) and discussed polar aligment [Read More]