The Scruffy Astronomer

I'm a refractor guy. I've seen these things called Schmidt-Cassegrains, and someone told me they can do astronomy with mirrors. One day I might be beguiled by the hyperbolic surfaces of a Ritchey-Chrétien, or the pure beauty of a well-machined truss tube. For now, though, I reckon that if it was good enough for Galieo, Kepler, Brahe and Copernicus, then it's good enough for me. But refractors have their problems. Chromatic aberration, where the different colours components in the light from stars don't focus at the same point, is the bugbear of the design. Of course, other designs do have their problems. Newtonians have coma, Schmidt-Cassegrains have astigmatism, and Ritchey-Chrétiens have an air of intolerable smugness (with apologies to the late Douglas Adams) So how do we manage chromatic aberration? We have two main ways of controlling the way light changes as it passes into and out of a glass lens. First, the amount the light bends is determined by the ...

High clouds! I've been taking photos of star clusters for a while now. I've been trying to demonstrate how much people with small telescopes in the city should be able to see. This one didn't go so well. Clusters are not only pretty, and most don't need lots of magnification. They're also largely immune from the city's light pollution. So I went out a week or two back to the dark sky site with my largely autonomous equipment all programmed to take photos of five different clusters. I set up, polar aligned, sorted out the inevitable technical problem that cropped up (urghh) and then got started on the first of the five targets. The night was pretty good, with the Moon setting in the west and not being too much of a problem (remember star clusters aren't badly affected by stray light). The first two images went without a hitch, and so I decided to leave the telescope doing what it was programmed to and I retired to my tent. ...

Chromatic aberration can have a significant effect on your binocular's performance, especially when looking at views with high contrast. it results in poor focus and colour fringing. This article explains what chromatic aberration is, and why high contrast makes things worse. When I'm talking about binoculars to customers, most often bird watchers, but also hunters, we often discuss how they might perform in high contrast environments. What, you may ask, are these? And why is it important? The answer is associated with chromatic aberration . A while back, I was out at Lake Acraman in the South Australian outback. We were out for geology, but of course, we were also looking for birds. Because we were in the desert, the sun was shining strongly, and the shadows cast by the trees are deep and sharp. My mate Dean had a pair of Vortex Razor binoculars - a magnificent tool. Being newer to birding, on the other hand, I had a far less salubrious pair - a stopgap while I saved ...

Caution - weird photographs ahead!   Getting the colours You might remember me talking in the past about the different ways you can represent the light you capture in your camera. You can display red light as red, but more interestingly, you can display the light that comes from different elements as different colours on your computer display. This is particularly good for separating light from two gases, say, Hydrogen and Sulphur, which are both reds. You can display one as red and one as green. When I take photos, I use filters to capture different colours. For foreground stars, I typically capture using broad “red”, “green” and “blue” filters, and for background nebulas I use Hydrogen, Oxygen and Sulphur “narrowband” filters. Presenting the colours Later on, in my imaging process, I recombine these channels in any way I find aesthetic. A couple of weeks ago, a new version of my image processing software ( Astro PixelProcessor ) was released. One of the new features is that I ...

Just about everyone in Australia is now familiar with having to live in and breathe this type of smoke. The 2019-20 bushfire season is a horror. The scale of the destruction of bush and agricultural land, let alone hundreds of buildings all around the country is impossible to estimate with any level of accuracy. Add to that the human toll and it's hard to comprehend. The smoke has been visible on satellite photos, and it’s even spread as far as New Zealand. I took this photo while walking in my local park. The smoke was particularly bad that morning, and the smell was unavoidable. That's the bush going up. Of course, above all that, the sun was shining. That morning we'd been greeted by a lurid sunrise. It was filtered so heavily the sun was easy to look directly at - not that I lingered, I've been well conditioned not to look at the sun. Of course, I can't help thinking in terms of photography, and on the way home I noticed the shadow I was casting seemed to have a...