The Scruffy Astronomer

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 ...

Back in May, I posted about spectrograms . This is a way of recording a bird call (or any sound, for that matter) in a visual way. You can think about it as a pianola roll, only much more detailed. With a bit of practice, you can actually read a spectrogram and "hear" the bird in your mind. You can even pick what sort of bird it is from the shape of the specrotrogram. Here's an example for you to guess. The other day, I was out getting takeaway when I heard a bird call. It's a bird that turns up each year now in Melbourne about this time. It used to be quite a rarity, but as the years get warmer, I'm hearing them nearly very year. It was not far away from me, and the background sound wasn't too loud, so I was able to get a recording on my phone with a reasonable signal-to-noise ratio. When I got home, I used Cornell University's free Raven Lite 2 software to convert my recording to a sonogram.  The sonogram As you can see, the main note - those four black ...

I was chatting to someone a few days ago, and the subject of old photos came up. I have very few: this one is from the late 1970s. At school, we had a 4" Unitron refractor on an equatorial mount. We could take photos of the Moon, but deep sky objects were beyond us. Apart from the cost, taking single, long exposures was supremely difficult. The longer the exposure, of course, the better the photo, but how do you keep the telescope on the target? To guide the telescope, a second scope was mounted on the main scope. This one had more magnification, and an eyepiece with a crosshair. The operator would peer through the eyepiece for the entire time, staring unblinking at a star. The operator would compensate for drift with the mount's slow-motion controls, but these were the only movements they could risk. If the operator lost the guide star, the photo would be ruined. Because of the long exposures, a wasted photo would cost of a lot of time. It was a terrible j...

Today's summer solstice post is overshadowed a little by the Grand Conjunction between Jupiter and Saturn. I know you'll all be out watching that - weather permitting, of course, I wrote this post a week or so beforehand. After that, Saturn and Jupiter will go hiding behind the sun, but there are still plenty of things to watch in the sky, including Mars, which is still high, although it's beginning to get small as it moves away from the Earth. I've added a couple of clusters to my list this time. I got both of them from my light-polluted back yard a week or two back. This is my photo of M41, which I took from my back yard using a saxon 1021 doublet refractor of the type that many of you have bought for Christmas. It's very similar to our most popular refractor, the saxon 909AZ3, just a tiny bit bigger. I had it on a tracking mount though, my own NEQ6. This photo gives you an idea what you're likely to see with a small telescope. The photo also shows a fair a...

Telescope mirrors are delicate, right? Dust degrades your image, right? Can a bit of dust damage your mirror? So what happens when you shoot one with a gun? Reflector telescopes are a great way of getting some serious aperture onto a deep-space object like a nebula or galaxy. The 10-inch Dobsonians we have give a relatively inexpensive, no-nonsense and, frankly stunning view of those hard-to-see, dim fuzzies, especially from a dark sky location. New owners of reflector telescopes always ask me how often do they need to clean the mirror. They seem surprised when I tell them that with care, they probably won't ever have to. Mirrors, particularly large ones, are very forgiving. How's this for a case in point? The Harlan J Smith Telescope in Texas is a 107 inch Cassegrain (with a Caudé option as well, for the technical). To put that into perspective, the ASV's monster in Central Victoria is "only" 40 inches in diameter. On commissioning in 1968, it was the t...

Padraic Koen posted this beautiful photo taken from the helipad at Arkaroola in South Australia. I often joke that my "office" is at the ASV's dark sky site in Heathcote, but Padraic's beats that by light years . It was at 3:59am on 6 December, and the camera, with its 11mm lens, was facing West-Northwest. Arkaroola is at the northern end of the Gammon Ranges, seriously isolated in the outback. The settlements of Copley and Leigh Creek are over 100km to the West-Southwest. These places produce pretty much zero light pollution, so the Arkaroola skies are about as dark as you'll get anywhere on the planet. There are a few things going on in this picture. First, the Moon was rising in the Northeast, out of frame to the right. This is shining gentle light onto the terrain, and the ten-second, ISO800 exposure picks out some features on the ground. This is pretty much my favourite part of the sky. At the top, Orion is dominating. Orion contains all sorts o...

What's the deal with magnification? When using a telescope for visual observations, it's a simple matter to calculate how much bigger everything looks. But with a camera it's more complicated. Here, two concepts  replace magnification: your field of view and your camera's resolution. One of the most common questions people ask me is about the magnification on telescopes. For visual telescopes, it's actually pretty simple. The magnification is just the ratio of the focal length of the main mirror or lens to the focal length of the eyepiece you're using. So, for example, if you've got a telescope with a 900mm focal length, and you use a 20mm eyepiece, the magnification is 900/20, or 45 times. Swap to a 10mm eyepiece and the magnification jumps to 90 times. This is why shorter eyepieces are more powerful. But people also ask me about about magnification when you're using a camera. There's no eyepiece, so it's more complicated.  It's about fie...