A little time ago I wrote an article for a Home Education magazine. It was a light look at how I started taking pictures of the sky and how others could easily join in. I thought this might be worth posting to my blog – so here it is …
“Always got her head in the clouds”
I was six years old and sitting in the classroom of my local village school. It had a large window which looked out across meadows & farmland. Today was summertime and I was watching the buttercups nod in a light breeze, bathed in a beautiful golden sunshine. My mind wandered, how amazing it all is from the beautiful flowers to the Sun and heaven knows what other fascinating things in the sky above.
“Jones!” yelled the teacher,”You’re not listening!”
“I am Miss” I replied, followed by a verbatim quote of the last 30 seconds of her lecturing.
Then I was punished, for showing off. I never really did get the attitude of schools & some teachers. What I did have was a fascination, a curiosity for all things ‘nature’, including the sky. Here started my voyage into Astronomy & Cosmology.
If you’re out under a clear dark sky one night soon, move away from any artificial light, turn off your torch and stare upwards. Your eyes will gradually become accustomed to the dark and more stars will come into view. Look for the milky patch across the sky, that’s the Milky Way, our own galaxy. It contains about 200 billion stars. The Universe beyond? Well there’s more stars there than all the grains of sand on all the beaches of our planet. And stars don’t account for half the matter out there.
Pictures & a thousand words
Another interest of mine is the use of cameras. I guess it really developed when I was a teenager but I have only fully indulged it within the last decade or so. Photographs can record a moment in time, a memory, that’s what most of us use them for. But that’s not all they can do. Some use them to provoke strong emotions, more than any passage of pros might do; take anti-war journalism for example. For others, the camera can show us sights that our eyes can’t – this is where one of my interests lies. Freeze the motion of a running animal with a fast shutter speed, take a macro shot of an insect feeding on a flower, point the camera down a microscope to reveal the tiny world around us; all these techniques & more, expand our awareness, our comprehension of the things around us. I suppose it was only a matter of time before I wished to put camera & telescope together.
If you have a camera that can take long exposures (more than say 30 seconds), take it out on a dark starry night, put it on something secure preferably a tripod, set the zoom to wide angle & point the camera upwards about 50 to 55 degrees (in the UK) & northwards. Experiment with the exposure time but start with 15 minutes or so.
The resulting image will show stars apparently rotating around a point (the celestial pole) in the sky. You’ve just taken your first astrophotography picture and have also demonstrated the spin of our planet on her axis!
With just a camera & tripod you can also take good pictures of the moon, aurora (if you’re lucky) and even record a few planets (Venus, Jupiter, Saturn, and Mars) but they won’t look very big, for that you’ll need a telescope.
Tamsin (our daughter) has, like most children, a wonderful imagination and it helps her jump from one thought to another. This was the case here. She had been thoroughly enjoying reading a series of books about “Stardust Fairies”. Within the tales, each fairy has their own special star; Regulus being one of them. Tamsin wanted to see Regulus (Alpha Leonis) so we checked on its positioning, first star of the constellation Leo, and pointed it out to her. Did you know that Regulus used to be called Cor Leonis, the lion’s heart, so it’s a star for all you courageous home-ed families out there.
We then became involved in a project to survey the darkness of Britain’s skies. To complete the survey you needed to count the number of stars that you can see in Orion’s belt. Tamsin loved it and from here it was but a small step to her wanting a telescope to further her interests in Astronomy.
We bought a 6 inch Schmidt Cassegrain (SCT) scope & an equatorial mount to put it on. There are several different types of scope; the SCT is probably the jack of all trades. It is good for planet viewing & deep sky objects and suited to visual or photographic use. The equatorial mount allows the scope to slowly track across the sky counteracting the rotation of our planet (as you photographed above).
The Low Down
So what do you need to get started? Well the great thing about astrophotography is that it’s easy, simple & cheap; it’s also difficult, complex and expensive. Did you get that? What I mean is that this is an interest that you can start off easily and grow it to become as involved as you wish.
Obviously some sort of camera is a necessity, your current one is probably sufficient for getting started. Modern digital cameras are great, they give you immediate feedback, are fairly sensitive and many have access to multiple settings. Read on for details of different techniques and what’s involved.
Please note: never look at the sun or image it without specialised filters – it could blind you.
Just a camera & lens can be used to take a broad picture of the night sky. Short exposures can be made on a tripod but longer exposures will need some sort of tracking mount. This can be as simple as a ‘barn door mount’ (search the web for plans on how to construct this for about £15) but is frequently done by ‘Piggybacking’ your camera on a telescope & mount whilst tracking. This requirement to track the sky for exposures above a handful of seconds is common to all astrophotography where you don’t wish to see the effects of Earth rotating.
Your telescope is all set-up and you’re viewing an interesting site through the eyepiece, the simplest way of recording this is t
o hold your digicam to the eyepiece & take a picture. There are things that you can do to refine this:
· Buy a digiscoping adapter to firmly hold your digicam to the eyepiece ~£30
· Match your camera lens to a suitable widefield eyepiece, specialist ones are available
· Set your digicam’s aperture wide open
· Use your digicam’s manual focus, set it to infinity & focus with the telescope
· Use a remote release or your digicam’s internal timer – avoid vibrations
Most of all experiment with different settings & targets, get to know what effect each change makes and have fun.
This is the main technique for serious astrophotography. The telescope is all set-up and the camera is attached via an adapter directly to the telescope. There is no camera lens between scope & camera; the telescope focuses light directly on to the camera’s sensor or film. The camera itself may be a SLR (Digital or Film), a specialist cooled astronomy CCD, or in some cases a webcam type video camera.
Most people would accept that the Digital SLR now has an advantage over film. You will need a ‘T’ adapter for your camera make, to attach it to the scope camera adapter. You will also need a remote shutter release cable. The ability to connect the camera directly to a computer is also helpful. A 90 degree viewfinder attachment can also help to avoid the need for limbo dancing lessons. (That or a good osteopath). Focusing can be awkward – autofocus is unlikely to work for all but the brightest objects. It is best to find a bright star & focus on that, then leave the focus alone for the night if possible – do take a test shot to check your focus. There are computer programs that can help you with this. Also worth noting is that most standard cameras have an infra-red filter (needed for normal daylight photography) and this reduces their astronomical sensitivity. Only Canon have made a specialist astronomy DSLR, the 20Da, but several conversions are available, particularly by a company called Hutech.
These devices are very sensitive to light; they are typically cooled to 20 degrees below ambient for noise reduction. They are however, very expensive & can only be used for this one purpose. At £1000 – £4000 this is definitely the hard core end of the hobby. They are controlled from a computer and can produce stunning images. Imaging is usually done by taking four sets of images using a filter wheel, 1 set for luminance & then 1 each for Red, Green & Blue; however ‘one shot colour’ CCD’s are available. Do not however under estimate what can be achieved with a DSLR.
This is a relatively new technique and is especially suited to planetary imaging. A short spell of video, perhaps 1000 frames, is recorded straight to PC. Each frame is then analysed by a computer program and the best are stacked together to build a detailed image. The advantage of this is that moments of good ‘seeing’ (I.e. when the atmosphere is still) can be caught and used, whilst more ‘wobbly’ moments can be discarded. The standard software for analysis & stacking is called Registax. You can build your own camera or buy a commercial one such as Celestron’s Neximage (about £90).
CCD / DSLR Processing
Typically when imaging a deep space object (DSO), you will be taking multiple exposures of the object. These exposures are called lights and they will be stacked together in a computer to create a far more detailed image. You should also be taking exposures called darks & flats. Darks are taken at the same temperature & settings as your lights, these will be used to correct the lights for hot pixels & circuit noise. Flats are taken at the lowest ISO setting of your camera and are of an evenly illuminated object, a lightbox or the evening sky just after sunset. These flats are used to correct your lights for vignetting and dirt on the imaging train. You should also take darks for the flats, no I’m not kidding! There’s various software available to help you with this process some commercial some freeware, Deep Sky Stacker is an easy start but my preference is for Iris.
I am not going to go into telescope choice very deeply here, everyone has there own preference & budget. But there are a few pointers:
· Don’t buy a Department Store special, do buy a proper astronomical scope
· Refractors will give you stunning sharp images but they’re expensive per inch of aperture and you’ll want an APO version to keep colour issues to a minimum
· Newtonians are cheap for large apertures but don’t always convert into a photographic instrument without hitches
· Catadioptics are a large group that inhabit the middle ground and are my preference, there are different types:
o Maksutovs are good visual instruments but can be a bit slow for imaging
o Schmidt-Cassegrains are a good all round scope that won’t break the bank, this was our choice.
o Ritchey-Cretiens are the desire of many an astrophotographer. Not cheap but superb for imaging – this is the basic design of Hubble.
Sooner or later you may wish to take images that require an individual exposure time of more than a minute or two & a reasonably long focal length e.g. 1500mm or more. At this point the tracking of your telescope mount may not be accurate enough, now you need a guiding system as well. This will either manually or automatically correct the telescope position at short intervals, on top of the equatorial tracking. The details of this are many, definitely beyond the scope of this article but you should be aware that several methods exist and there are several interest groups on the internet that will be willing to advise you.
I have tried to give you a brief outline of Astrophotography. There are many wonders to see, they are inspiring, they put us into our proper perspective and they are beautiful. A telescope alone is a fantastic resource for any home educator, but add a camera to the plot and you will see many more beautiful wonders.
Stardust Magic by Moonlight Linda Chapman ISBN 0141317795 Well, it inspired Tamsin
Starware Philip Harrington ISBN 0471418064 A guide to all the kit
strophotography The State of the Art David Ratledge ISBN 1852337346 You really need this book
Stars & Planets Ian Ridpath ISBN 0751327123 Finding your way around
Astronomy for Dummies Stephen Maran ISBN 0764584650 A crash course in the basics
What are you waiting for? Go put your head in the clouds.