Showing posts from 2021

Processing an LHaRGB image using monochrome and colour cameras, different pixel scales and Astro Pixel Processor

Nearly nobody reads these blogs, and so I’m going to write one which is pretty much for my own benefit. I normally take notes about my workflow. I rarely actually follow them, normally getting distracted and going off on tangents, but in this case I was so out of my depth (I even needed help from a Dutch expert) I decided to figure it out beforehand, actually follow it, and record it here. Perhaps someone will benefit from the work I've done. Perhaps that person will be me. If you’ve found this blog using Google, and you’re after the actual workflow, scroll down to the section called “processing the data”. Finally, a chance for a photo A couple of weeks ago I visited the ASV’s dark sky site. It was the first time I'd been there for a while (thanks to successive COVID lockdowns) and I was looking forward to taking a decent image. In the time, I’d taken other astrophotographs, but the aim of those was more as a test for equipment, rather than the image itself. No, this was a t

Frankenscope and NGC1365 - the Great Barred Galaxy

Finally, an image! I've finally got around to processing an image of NGC1365 - the Great Barred Galaxy - that I got from the ASV's dark sky site in Central Victoria a couple of weekends ago. It isn't the best image I've taken, but it's interesting, and it's my first serious image since before the pandemic! But it was a challenge - I made things hard for myself by using two scopes, two cameras and one very rusty astrophotographer.  Frankenscope! The colour information in the image was gathered in 51 five-minute exposures using a colour camera on a Sidereal Trading modified telescope. This is one crazy machine.  The front half - the objective - of the scope is a saxon 102mm FCD100 triplet, which is a beautiful piece of glass. We removed the somewhat unworthy focuser and replaced it with an Astroworx Crayford focuser made in our own factory. This focuser will soon be launched onto the market, and we hope it will do well. The guide scope was made by Sky-Watcher, t

The tale of a cataract as told by an astrophotographer

Sight, in humans, is quite a popular thing. People regard it highly, and do seem to think it's an overall good idea. My experience of sight has been, like most other people, a given. It started great, and as a kid my family would occasionally use me to find things, like shop signs, in the distance. Of course, it does deteriorate over time, and I've worn glasses since early university. It started just for reading, but soon I was wearing them full-time.  It turned out that apart from being long-sighted, I had astigmatisms which were reasonably severe, and getting worse.  You get old Eventually I wasn't able to look through telescopes any longer: unless I had an eyepiece that I couldn't afford, the eye relief - the required distance between the eyepiece and your eyeball - was so short that I had to remove my glasses. Without glasses, of course, all I could see were comets. No, they weren't meant to be there.  Resignedly, I gave up visual astronomy and went deeper into

Video - unboxing the saxon Astroseeker 15075

We've uploaded another video onto the Optics Central YouTube channel. This one is me unboxing the saxon Astroseeker 15075. This is a 6-inch Newtonian on a light computerised alt-azimuth mount. The mount is a nifty little unit, well capable of carrying the weight of the tube. It's a heavier duty mount than the SkyWatcher mini AZGTi, and is capable of taking a heavier tube than the Newtonian here. In fact, this mount is often found with a 127mm Maksutov. The mount can be controlled by the hand controller that's included in the box. Alternatively, because the newest versions of the mount have a built-in WiFi connection, you can also control it using the SynScan app for your phone. The tube is a standard Newtonian, with a parabolic mirror and a focal length of 750mm. This makes it an f/5, meaning it's good for deep-space objects, such as galaxies and nebulas. Star clusters and the Moon are also well within your reach, especially in light polluted areas, but planets wi

Abbe numbers and refractive indices

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-Chr├ętien, 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-Chr├ętiens 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

Prasun's Uluru - a double-stacked astroterrestrial photo

I've shown astroterrestrial photos before, photos with a subject on the ground with a night sky background. Here's a stunning example. It's Uluru (obviously) from the viewing area with the South Eastern sky behind it. The photo was taken by Prasun Agrawal a little while back, and I was knocked out by its quality. I love the hook shape of the Rho Ophiuchi cloud complex near Antares. But there's more to the image than than this. You can easily see details in the rock, such as Kantju Gorge on the mid-left, that interesting line of circular features in the centre of the rock, and bushes in the foreground. It's an unusually high level of quality. How did Prasun do it? It's a composite: a common way of producing this type of image. Single images are more challenging as you need to focus separately on foreground and background. With a composite, you take a single foreground image and combine this with a "stacked" image of the sky. The stac

Problems with the Hubble Space Telescope

The Hubble Space Telescope has been in orbit since 1990. That's incredible for the high-radiation environment it has to work in. After a shaky start, it's been sending mind-boggling photos back to Earth for more than 30 years. Image: NASA But a few weeks ago the payload computer stopped. The computer equipment on board the HST has many levels of redundancies: there are backups for their backups. So the first problem is identifying the component that has failed. But even after they've found the problem, NASA can't just go up there and start soldering. Since the retirement of the Space Shuttle, they have to do it all remotely. What's currently up there is going to have to do. What's more, while many astronomers on Earth communicate with their equipment at a distance, remote maintenance is difficult when it might be the remote computer that's gone on the fritz! There are a few suspect parts. Initially, NASA though it may have been a bank

John Iramiyan's M16, the Eagle Nebula in narrowband

Just take a look at this photo of M16 - the Eagle nebula. The Pillars of Creation are right in the centre of the image, and to the left there's the Stellar Spire. Note the horseshoe shaped structure at the top of the nebula - I'll get back to that. John uses a saxon 127mm FCD100 triplet refractor. This is one of the big ones. For an imaging array, John uses the popular ZWO ASI1600MM-Pro monochrome camera and shoots through narrowband filters. All his exposures are four minutes long. John has presented his image in the so-called "Hubble Palette", where images taken though the Sulphur filter are shown as red, those taken though the Hydrogen alpha filter are shown as green and those taken through the Oxygen filter are shows as blue. As a contrast, here's one of my own photos of M16. It's taken with similar equipment, an ASI1600MM-Pro, a slightly smaller 107mm triplet refractor and narrowband filters, which are presented using the Hu

Viewing targets for the Winter (June) solstice 2020

With the winter solstice coming up, it's time to send around my regular viewing list. Those of you who have small telescopes or (like me) are stuck in the city, start by searching for clusters, either open clusters (which are pretty groups of stars) or globular clusters (which are tight spectacular swarms). Once you've done that, start looking for double stars, which are pretty in a different way. One day I'll get around to photographing some... For planets, Saturn and Jupiter are currently your best bet. Here's a photo I took of Saturn. I used budget equipment (about $1000), which I was testing for work. Open cluster: Mel 111 - Coma Berenices Star Cluster (06:55 PM) Galaxy: M 87 - Virgo A (01:55 AM) Galaxy: M 104 - Sombrero Galaxy (02:09 AM) Dark nebula: C 99 - Coalsack Nebula (02:24 AM) Open cluster: NGC 4755 - Jewel Box Cluster (02:24 AM) Galaxy: NGC 5128 - Centaurus A (02:52 AM) Globular cluster: NGC 5139 - Omega Centauri (02:52 AM) Galaxy:

Illuminated reticule eyepiece

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

Getting to Mars

There have been a lot of spacecraft arriving at Mars in the last few months. Since February, the US, China and the United Arab Emirates have all arrived there. The US and China have now landed, and the UAE will remain in orbit. The soviets did it ages ago, of course. Here's a model of their probe. This is all very cool, but more interesting is how they reached Mars, and why all three arrived at about the same time. How do you get there? I probably don't have to say this, but getting to Mars isn't as simple as hopping in your car and driving to Mildura. One of the complexities of rocket science is that to have fuel available for manoeuvre s such as landing, you have to lift that fuel off Earth's surface, and that takes ... well, fuel! How do you get to Mars using the absolute minimum amount? You figure out the shortest way. Mars is one planet out from the Sun. Because of this, it orbits slower than Earth. A Mars "year" is about 23 Earth

What type of telescope is best for me? A really rough guide based on what you want to see.

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

Review of the saxon FCD100 127mm triplet APO

  To be honest, I never thought I'd have the privilege of mucking about with a 5" triplet refractor. I love this job! Introduction The saxon (note the lower case) FCD100 series comes in three sizes, an 80mm, a 100 and the monster 127. It's this last one ( I'm talking about here. This is a variant of the scope sold as the Explore Scientific 127ED (, however there are a few differences. The focuser on the saxon is the standard barrel-type, where the ES model has a hexagonal focuser, which may be rated to a higher weight limit. First, the basics. This is a five-inch air-spaced triplet apochromatic telescope with Hoya FCD100 ED glass. That sentence alone should have you either bewildered or drooling. Suffice to say, it's a large, high end refractor. Its