Six moons and a planet

In the race to take best resolution images of Jupiter and Saturn at highest powers and frame rates, the moons often get neglected. Personally, I do like to see entire systems with their ever-changing view.

Of course, the moons are fainter than the planet so usually the planet will be terribly overexposed when the moons are imaged. At the cost of photometric unscientificness, this can be overcome by merging multiple exposure times in a single image. Here is one of Saturn that shows six of its moons, including faint Hyperion at around 15th magnitude.

And because that is really just a lot of dots without context, here is an annotated version

The process I use is to take a few short exposure frames as for normal planetary images, then one or two longer exposures, then repeat. Each of these frame sets is combined into a meta-frame by some scripting fu that attempts to pull signal from the longer exposures into the dark areas of the shorter exposures. The composite frames can then be stacked as usual. I made a similar one in March for Jupiter

For that one I actually took a gazillion frames over three hours in the hope of making a video out of it once I fully automate the compositing process. Unfortunately I seem to be building up a bit of an image processing backlog. Even now, while I’m trying to reduce the pile, the sky turned clear and the telescope is collecting data outside – argh!


First light for Galileoscope

Ok, so I said in my last post I was going to wait for something to mount the Galileoscope on before attempting to take an image with it. But last night turned clear unexpectedly and the full moon issued the challenge: Can you fit me on a chip?

Yes, I can. Connecting the camera to the Galileoscope was straightforward. Taking an image hand-held is a trifle more challenging, basically the only way to do this is to start recording video and then pointing the tube at the object until you get enough frames that contain the object (of course, this only works for bright objects where exposure times are very short).

However, even with the reduced pixel scale of the Galileoscope my chip was to tiny to fit the image of the full moon. A 0.5x focal reducer was needed, but this turned out to require more inward focus travel than the scope was ready to give willingly. So I had to make do with unwillingly:

I NEVER run out of inward focus travel

I NEVER run out of inward focus travel

The advantage of having a cheap telescope with a flexible plastic tube assembled from a kit becomes apparent: Easy to partially disassemble and bend to your will.


A six-pack of telescopes

After seeing an image taken with a Galileoscope posted on the Astronomy Forum, I decided to order one to play around with it myself, and to evaluate its usefulness for astrophotography. However, it turned out to be difficult to obtain one at a good price in Europe. Only a few sites had it in stock, and the cost including shipping would have been around €70 ($100).

Originally introduced as a $15 telescope for the international year of astronomy 2009, it is now sold at the Galileoscope website itself in packs of six units for $150, i.e. $30 apiece. This seemed to be the most cost-effective solution, even with shipping costs of $140 added on top. The delivery arrived last week so I am now the happy owner of 7 telescopes. Of course, I neglected to consider customs for importing from the United States – another €45 ($60).

Opening the first kit revealed that there was more assembly involved than I had expected: A total of 31 parts form a motoric challenge that needs to be addressed prior to first use. However, assembly requires no tools and the provided instructions were clear enough. In fact, building the scope is an interesting and enjoyable experience, and demonstrates that a refractor really is just an empty tube with bits of glass at the end.


The first completed telescope


I tried the scope on terrestial objects first and later on Saturn. The first thing I noticed is that is really hard to keep anything in the field of view without a mount. And it is next to impossible while focussing the scope, which in turn makes it hard to achieve good focus. It is therefore advisable to practise while it is still light (but well away from the Sun!) when any direction will at least show you something.

The Galileoscope is a 50mm refractor with a focal length of 500mm. Like my Celestron, it is therefore an f/10 scope. A 20 mm eye piece (with plastic lenses but acceptable quality) is provided, this yields 25x magnification and a field of view of about 1.5°. Also provided is a dual use secondary lens that can be configured as a 2 x barlow (yielding 50x at 0.75°) or as a Galilean eyepiece (upright image but almost no field of view). Using the barlow I was just able to make out the rings of Saturn despite the planet erratically jumping through my hand-held field of view.

However, the real feature that makes this little scope more interesting than its cheap department store counterparts is that it comes with a standard 1.25″ barrel. It is therefore possible to connect all the accessories you already have or plan to splurge on. For example, below is the Galileoscope with an 8mm Hyperion wide-field eyepiece. It gives a very usable 60x magnification with a true field of view of about 1.1°. A small drawback is that the barrel does not have a thumbscrew but relies on friction from plastic ridges alone, which does not feel safe for a heavy and expensive eyepiece.


An 8mm Hyperion wide-field eyepiece all but outweighs the actual telescope, giving the setup the characteristics of a cudgel (the price imbalance is probably even greater)

Speaking of field of view, this is usually given as 1.5° for the Galileoscope. However, that is simply the value achieved with the standard eye piece and not a limitation of the telescope. A 40mm Ploessl yields a 3° FOV at 12x magnification. For the fun of it I tried adding a 0.5 focal reducer. At this point a limitation at about 5° became apparent but this is to be expected from the limited size of the pupil (minimum usable magnification). It would be interesting to connect a large chip camera at prime focus to determine the limiting FOV.

However, what I have is a very small chip Flea3 camera and at this point I’m just itching to try the scope with it. At first it may seem silly to make photos with a cheap 50mm scope when you have a 200mm (8″) scope, but actually there can be benefits

  • 4 x larger field of view even for the tiny chip, possibly just enough for full moon
  • For extended objects, light intensity per pixel is not reduced compared to a larger scope (both are f/10). In fact it might be slighlty better as the refractor does not have the obstruction of the secondary mirror
  • The reduced pixel scale allows for longer unguided exposures

However, this will have to wait until I manage to connect the scope onto my Celestron. A Celestron piggy-back camera adapter is already on its way, if this is successful I will most certainly post the results here – watch this space!

Added Blog and Gallery to Site

Welcome, all you visitors that are now magically attracted here from all over the world. This is the place where I will share my adventures in urban astrophotography from a 15th floor balcony in central The Hague, Netherlands, using an 8″ catadioptric telescope and a Flea3 industrial camera (feel free to have peek a into the gallery!)

Although this was the main motivation for creating the blog and the gallery in the first place, I have other interests related to image processing, computer graphics, and software development, and may also write on these things (or off-topic rants). This is my first attempt at blogging so I myself am curious to see how this will develop.

For the last 7 years, I maintained as a purist static HTML site, without PHP and using only Notepad as editor and a command line ftp client. However, the large overhead to write and publish proved to be restrictive, so the content was both limited and frequently outdated. I hope this WordPress-based blog and gallery reduces the hurdle to publish images and thoughts on a timely basis.

Clear Skies!