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 ...

During the latest lockdown in Melbourne, I was at home, but had taken with me a small Newtonian telescope and a guide camera. I was wondering what sort of photo of Jupiter I could get with simple and inexpensive equipment. I put the scope up onto my NEQ6 mount, but it didn't have a finderscope. Complicating matters, the guide camera was set into the focuser of the telescope and it was nicely focused. I didn't want to move it. How was I going to see where the scope was pointed? How was I going to align the scope to the sky? Reusing old equipment I have an old guide scope at home - an Orion. It's not as good as the saxon one, but it does the job. I've also got an ancient illuminated reticule eyepiece which I rescued out a junk bin at an astro meet once. I planned to use this in the guide scope. The eyepiece was filthy. When I looked through it, all I could see was nicely-focused grit and dust across the whole field. I had to pull the eyepiece apart to c...

Classifying telescopes When clients come in and ask about a new telescope, the first thing we normally ask is what they want to see with it. People often look at us weirdly when I ask this. "The sky?" they tend to venture. We're after an idea whether they want to look at planets or deep sky targets like nebulas and galaxies. What we're getting towards is what type of telescope is best for them. Telescopes aren't the same. They're highly specific tools, each with their own area of specialisation. Get the wrong one and it's not going to give you what you want. Ferraris and Land Cruisers We explain by asking people what is the best type of car: a Land Cruiser or a Ferrari? They're both great for what they're intended for, but used for a different purpose... not so much. So how do we decide what type? Aperture and focal length Telescopes are fairly comprehensively described in two measurements, aperture and focal length. Aperture - how much ligh...

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 ...