As with the art explanations, this introduction to our Astro-imaging section isn't intended exclusively for those folks who might have a specific interest in astronomy or Solar System imaging in particular: as the site develops more detailed information on capturing & processing these objects will be included for these people , explaining more advanced techniques etc...but the following has been written just as much for those people who find the images interesting in a more general way & merely wish to have a rough familiarity with how we go about creating them! J
This section makes no mention of the imaging of what are termed "deep space" objects like galaxies, nebulae or similar objects - this is an almost completely different type of imaging with a very different approach...& whilst we occasionally do this type of imaging it is not our particular forte.
Photographing/imaging the Sun &
Moon is, however, very similar to planetary photography & you will see a
section dedicated to these objects on this website! J
Having said that, planetary imaging does require a certain amount of insanity/obsessiveness to achieve good results (like art!) We often need to travel around the countryside in what is termed "chasing the seeing" to find somewhere that the meteorological indicators predict will be good for imaging on any particular night - & like all weather forecasts we often find out that the conditions aren't really as good as predicted!
The ideal indicators are in an area of the countryside where the surface winds & also high altitude winds (ie, the jet-streams) are relatively slow & smooth & all heading in the same general direction, which is often not the case - & of course no clouds!
This means looking at the
weather predictions on the internet & going to a favourable place,
ideally somewhere situated on a large flat plain so that the winds travel
smoothly without bouncing up & down as they do in hilly terrain: but
quite often good conditions can be found where the location & forecast
doesn't suggest so - & of course vice-versa...so there really is an large
element of gambling involved!
Planetary imaging uses high magnifications (termed image scale, or focal length) & requires well-made lens/optical systems: some folks might recall historical photographs or drawings of old telescopes that appear to have insanely long tubes held up to the sky in absurdly fantastic ways...this is because in the "old days" some of the (often) limited optical qualities of telescopes were countered in this manner as well as giving high magnifications. :)
It is the
very fact that we need this long focal length or high magnifications to
create our images that puts such demands upon the weather or
"seeing" conditions - everything, including little atmospheric
variations in wind etc are magnified enormously - & when you consider
that those little points of light in the sky we see with our eyes are
magnified to the size of a tennis balls on the laptop screen, it gives you an
idea of the magnifications we use..!
For planetary imaging we currently use a Celestron 14-inch SCT, this telescope being one of the best "off-the-shelf" types for this undertaking; they are compact (which is good!) but still possess a long focal length (ie, magnifying potential) through being able to fold the optical system back & forth in a short tube to keep the whole setup compact: the photograph adjacent shows how our scope appears when set up ready to image with various cables for powering & controlling it, plus the auxiliary equipment. Being "14 inches" (350mm) indicates the size of the main optical element...giving us the ability to "see" & magnify things much like as if we had 14 inch pupils in our eyes!!! The freeware computer program "FireCapture" is also shown open on the laptop screen, ready to start capturing images: the bright "star" seen in the background is Venus, the "evening/morning star."
We conduct "mono imaging" where we record multiple videos with each different filter one after the other...red ("r channel") green ("g channel") & blue ("b channel") which are processed separately & then combined to make a full-colour image. ("rgb") Colour cameras can also be used which display a full-colour image during capture & processing: these are very good at showing what's happening with a telescope to a group of people at the same time. We were given one of these to test at one stage & we used it in an image on this page to provide a more graphic illustration of the particular computer processes we employ.
Other special filters such as various wavelength infra-red ("ir) are also used to reveal other details not seen with colour images - & the individual r, g & b images we obtain can also reveal specific details in their particular wavelengths.
The filters are loaded into a revolving chamber much like the old "six-shooter" of the Westerns, except this is a 7-shooter with 7 filter chambers! J We select whichever filter we wish to use via the computer screen. The actual filter chamber can be dimly seen in front of the cherry-red camera itself, which has a blue cable attached...
A special focuser is required for the telescope that features a digital readout display so that we can accurately focus the onscreen image & also note the display reading for the next capture - each channel usually requires a different focus setting & this might alter constantly during a long imaging session...this focuser has the white cable running from it - & the dim green screen to the left of the laptop is the digital readout screen.
Focus is very important: I liken the activity to being very similar to the tracking skills of my ancestors, where faint but nonetheless real details exist amongst the multitude of confusing background information - but in this case the confusing information is all the noise etc on the computer screen & the planet itself often appears rather hazy because the noise is covering it also, making it very difficult to judge best focus. (noise is similar to the appearance of a television image when the reception is very poor) With the focuser we use we can (theoretically) make adjustments in 2 micron steps (in practical terms 4 to 8 microns is the accuracy we usually apply) and when you consider that the average human hair is 100 microns thick you get an idea of the tiny adjustments we are making to get the most accurate focus...
most important element for successful imaging (along with good seeing &
focus) is collimation or "fine-tuning" of the telescope...this can
be viewed as vaguely akin to the fine-tuning of a racing-car engine to get
the best performance: it needs good seeing conditions and a scope whose
optical components have reached a similar temperature to the surrounding air
temperature to collimate properly, just like for the imaging itself - &
why we collimate immediately before the actual imaging session. This is the
reason why we have a dual-temperature gauge on the rear of the scope, to tell
us what both temperatures are...& we try to keep a 1°C or less difference
between them through various means when we image.
When everything is ready video movies are taken of a planet using the chosen filters (r, then g then b in succession for a full-colour end-result) & then we use special software (much of it free! :) ) to look at each frame of each video/movie: this grades them from best to worst frame in terms of quality/appearance & allows you to choose however number of the better frames you wish to use...
These are then selected & stacked together in the same program to create a single image which is best described as being " smoother & able to be developed to show far more detail" than any single frame image could ever be...by using additional software programs to sharpen this "stacked image" into something far superior, or for that matter much better than anything that you could ever expect to see by looking through the telescope with your eyes...
Other programs complete the final stages of image-processing: Photoshop is one well known program that we utilise to put the "final touches" to the images, & can also be used to create "animations" where we produce a "movie" showing a planet rotating, with its' moons circling around it at the same time...
Adjacent is a colour example of the basic progression of image-processing described, using Mars & showing what we judged as the best single frame (left) of the video, then the stack of around 2000 of the best frames from the video (middle) & that stack "sharpened" & enlarged to display the details best (right)...this is not a very good example, done with a colour camera on an average night but it does demonstrate fairly well the end-results of what I have just been explaining here: the white patches at opposite ends on Mars are the North & South Polar regions whilst those soft white patches towards the upper left are actually clouds floating in the Martian atmosphere.
In each specific planetary images section you look at you will see some of the results of our activities, plus additional information on any particular planet...
And remember - although it might appear
very involved we are actually out there sitting under the night sky for much
of the time when we do this: shooting
stars, some of them real fireballs,
the magnificent Milky Way, all the rising & setting stars (which might
also include The Moon) & a host of other fantastic occurrences from night
birds to luminous bugs are constantly parading around us as we sit there -
making us feel very much alive..!