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By way of introduction

 

This isn't a website aimed at visual observing, or telescopes in general, but at how to capture images of astronomical objects and phenomenon. There's a reason for this, which is that there is plenty of information already written about the basics of astronomy, and that telescopes have in many ways developed as much as they can, and again there is plenty already written about scopes and how to choose and use them. However, in astrophotography, the digital revolution is putting equipment in the hands of amateurs which 10 years ago would have pleased most professionals, and 20 years ago may not even have been invented. The revolution is continuing, as digital products get both cheaper and more advanced.

So why take photos of the sky's objects? I don't intend to write a blow by blow account of how to be an astrophotographer, but in the blurb heading the individual sections, you'll find a few hints about how there are different techniques depending on what you're trying to capture.

There are two basic premises:

Why is so? When you try and look at things outside the atmosphere of the earth, you're up against two problems. The atmosphere is not a static piece of clear air that is optically perfect. It is turbulent - in the same way that running water distorts what is seen through it. It also is not completely transparent. Clouds are the most obvious forms of this problem, but even on nights of good seeing, you'll see the orange glow of townlights scattering off particles in the atmosphere. So instead of looking through a nice still pool of crystal clear water, we're actually trying to look through the equivalent of the Manchester Ship Canal. Bugger, we cry, and throw our telescopes into space, and call them Hubble or something with lots of initials to confuse the punters.

The second problem is not only that some of these objects are small and far away, but they are not very bright. The human eye is excellent for what it evolved to do - spot things, tell you how far away they are, then speak to your limbs via your brain so you can propel a sharpened stick through what is about to become your next dinner. However it has disadvantages. It can only gather light for about 2 seconds before it becomes saturated with whatever light there is, and after this time, gazing into the dark will not result in you seeing anything extra, not even if you eat a kilo of carrots a day. Secondly the human pupil is only 7mm wide if you're young, and shrinks to 4mm with age - so it's quite small. Thirdly, as the amount of visible light fades, human sight gradually goes monochrome.

There are ways around these problems; if you sit in a very dark room for an hour, your nightvision will be very sensitive. However one quick flash of a torch, and you've lost it again, for at least 15 minutes. A telescope works by gathering more light for your eye to see, then magnifying the image - a scope with a 70mm lens will gather 100 times more light than you unaided eye for example. But unless you have a very very clear sky, and a very very large telescope, whatever you see (excluding the planets) will be in black and white. You can drive to what is called a dark site, to escape the glow of city lights in the sky, which will allow you to see more. Some US amateurs I know have to drive for hours to escape this sky glow. What effectively happens is that city lights illuminate the particles in the sky, and the faint and fine details of the targets you seek are lost in the glow. The best example of this is the Milky Way. Easily seen with the naked eye in the countryside, but seldom, if never, in towns.

But (I hear you cry) what about filters to cut out the light pollution? And they do exist, but also cut a lot of other light out of the view, and can colour the image somewhat. They can't always make it as if light pollution isn't there sadly.

So the picture is that you're limited to black and white vision, facing either light pollution or long drives out into the sticks, and have to walk around with an eyepatch on to preserve your night vision. You will probably lust over larger scopes that will let you capture more light...... You'll pay for your neighbours to insulate their roof properly so you can see the planets at high powers with less thermal wobble...... You'll......

Stop.

Technology is at hand to rescue you. The advent of affordable digital imaging devices, from the humble webcam, through to professional DSLRs or dedicated astrocameras with cooling and all sorts has meant that many of the above problems are gone, or reduced to manageable levels. The use of webcams to reduce the effect of atmospheric wobble on planetary images gives you a form of adaptive optics (which cost millions) for 55. The DSLR, with a shutter that can be left open as long as you want, will gather more light than your eye ever could, and will give you colourful images, even if you strap on the most aggressive of filters. Then you can play with your digitally acquired images on your PC to clean them up and do other wondrous things to them. Yes, traditional photography is still an option, and indeed formed the biggest revolution in astronomy once it was applied to capturing faint stars - but as noted elsewhere, digital photography is hugely more efficient at capturing light, and does away with waiting for film to develop. In the same way the digital photography is taking over from film, so digital astrophotography is also taking over from film astrophtography. Even the quest for huge scopes can be held at bay with a good camera or imager - instead of increasing aperture to capture more light, just point it at the target for longer. Many imagers are now using 80mm scopes where once upon a time they wouldn't even have made it as spotting scopes.

So what's this all about then? It's just a point of view, of course, but I think that if you really want to see the wonders of the sky to their best, you can do a lot worse than invest in astro imaging gear.

 

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