Orwell Astronomical Society (Ipswich)
First Use Of A CCD Camera
At Orwell Park
In the late 1980s and early 1990s, amateur astronomers worldwide became increasingly enthusiastic and knowledgeable about the opportunities for astronomical imaging offered by electronic cameras based on CCDs (Charge Coupled Devices). CCDs offer much improved sensitivity over traditional photographic film and therefore make it possible to obtain impressive images of deep sky objects without long exposures. Several members of OASI became interested in the new technology in the early 1990s. Chief among the protagonists at Orwell Park was Ian Swann, who designed and built his own CCD camera and wrote software to process images obtained with it. On 19 May 1992, Ian became the first person to use the Tomline Refractor for digital imaging, using his home-built CCD camera in an afocal configuration. The following extracts from OASI Newsletters detail Ian's first attempt at CCD imaging with the Tomline Refractor, a later attempt after further development of the CCD equipment, and his subsequent trip to the COAA (Centre for Observational Astronomy in the Algarve) to test further the capabilities of his camera. Unfortunately, original CCD images from this era have been lost and the images below are scanned from poor quality prints.
Wednesday 19 May 1992 saw the first use of a CCD camera with the Orwell Park Refractor. Ian Swann brought to the dome his CCD camera with associated control equipment and a portable PC. We pointed the Orwell Park Refractor towards Jupiter and then mounted the CCD camera on a tripod positioned behind the eyepiece. We obtained an image of Jupiter on the PC screen as a blob with absolutely no discernible detail. It was difficult to position the camera accurately behind the eyepiece and we concluded that it would help if there were a properly aligned mounting facility. However, as no such mount was available we devised an alternative method and, in time-honoured fashion, attached the CCD camera to the eyepiece with a long length of sticky plaster from the first aid box. After much changing of the exposure time and gain controls of the CCD camera, three of Jupiter's Gallilean satellites came into view, together with a faint band across the disc of the planet.
Thursday 26 November 1992 dawned to the sound of heavy rain (that was to flood South Wales and the West of England a few days later). Obviously there was no chance of any astronomy that day! However, by early evening, the weather had changed completely! The rain had washed all the pollutants out of the atmosphere, resulting in very transparent skies. A phone call from Ian Swann bringing a request for assistance meant that re-laying some floorboards in my living room was deferred for yet another evening in favour of astronomical observing.
Ian has spent the last few months designing and building a CCD camera and, with some helpful comments from a number of the OASI Wednesday night regulars, was in a position to test the latest modifications. A CCD camera is a very sensitive device, controlled by computer, that produces image information electronically. An unfortunate drawback is that a CCD requires a large amount of ancillary equipment to be set up near the telescope, including a water filled, pumped cooling system. Anyone who has visited Orwell Park Observatory will know that the climb up the steps to the equatorial room is hard enough without carrying several crates of equipment. On this occasion we also had to carry up the steps a video camera which was to be connected to the telescope for guiding. By 21:30 everything was ready in the dome, even the obligatory band of cloud had disappeared, and we decided to test the CCD camera on a bright object. Both CCD and video cameras have a very small field of view so we decided to use the Pleiades for initial calibration, providing many stars from which to choose without having to move the telescope very far.
Our main target for the evening was to be the Orion Nebula (M42) and, although it was still at low altitude, following initial setup we began imaging. To our amazement, we found it possible to use the video camera fixed to the 258 mm Tomline Refractor, imaging the four stars in the Trapezium, for guiding. Meanwhile, the CCD camera, attached to the 100 mm guide telescope, configured to produce an image after a 10 minute exposure, provided a spectacular view of the Orion Nebula and, unfortunately, brought to our attention a fault with the drive mechanism of the telescope.
The video camera produced an image which we viewed on an external monitor. Its field of view was about 10 times the diameter of the Trapezium (approximately 47 arcseconds). Even the smallest correction in RA showed very easily and it was straightforward, despite the known worm error in the drive mechanism, to achieve accurate tracking in RA. However, the 10 minute exposure revealed a drift in declination of at least one diameter of the Trapezium, indicating a previously unsuspected problem. We moved the monitor close to the declination adjustment hand wheel on the Tomline Refractor and made another attempt to image part of M42. This time we tried a 15 minute exposure and used both RA and dec adjustments to keep the image of one of the stars of the Trapezium firmly centred in a 5 mm diameter circle drawn on the video monitor (we found this to be easily achievable). The resulting image was stunning, but our enthusiasm was tempered somewhat by the fact that it was past midnight and very cold!
We decided to try our luck on a new object: Mars. By now we were accustomed to the setup of the various instruments, and soon captured an image of Mars. However, in contrast with our success with the Orion Nebula, Mars was a washout and we could see no detail at all, only a bland featureless disk. We decided to swap the CCD and video cameras, attaching the CCD camera to the Tomline Refractor and using the video camera for guiding with the 100 mm telescope. This combination should have been ideal for capturing planetary detail (on previous occasions it had provided excellent images of Saturn). Unfortunately, on this occasion, this configuration did not provide a good image. It was time to use the telescope in its original mode: with a human eye rather than an electronic one at the eyepiece! This revealed that Mars was indeed a washout: there was nothing wrong with the CCD camera after all! We re-pointed the telescope back onto M42 and the new configuration revealed it in a glory that we had not previously seen, with strands of wispy nebulosity drifting widely from the central nebulosity. I was immediately reminded of the amazing photographs of the nebula taken by David Malin.
By this time it was nearing 02:00 and, despite the near perfect conditions, we reluctantly concluded that it was time to terminate the session, so we removed all the gear from the dome and took it down the stairs to the car park. Apart from the problem with the declination adjustment the session had been a complete success and, in particular, our views of the Orion Nebula had been incredible!
My first family holiday for five years had to have something special for all of us, so I suggested that we go to the COAA (Centre for Observational Astronomy in the Algarve). COAA is a centre for amateur astronomers and is within easy driving distance of all the attractions that southern Portugal has to offer. The thought of flying to a warm, sunny land for two weeks excited the whole family but for me the prospect of clear dark skies and the use of my CCD camera with a 300 mm Newtonian reflector was the main attraction! I have developed the CCD camera based on the new Texas 255 chip and have been frustrated in use of it by the lack of clear nights in Britain, so COAA seemed a great place to try it out.
Our decision made, we paid the deposit, bought some suitable clothes and studied the weather forecasts intently. All was set for us to depart on 16 May 1994. All went well on the outward journey. My wife and children enjoyed the flight, although my four year old son was a little disappointed that the aeroplane did not fly upside down at least once! As we disembarked, the warm local air made a pleasant change from the cool clinical atmosphere of the aircraft. We retrieved our luggage and caught the shuttle bus to pick up the hire car. The one hour drive to COAA was easy but I was nevertheless pleased that it was still daylight as we followed the map provided by COAA and negotiated the narrow country lanes close to the centre. On arrival at COAA, Bev and Janet Ewen-Smith, the English couple who own and run the centre, gave us a warm welcome. Within COAA, Casa Adelina is Bev and Janet's home, and it is to their great credit that they open up much of it to their guests. The house is divided into apartments, each with its own facilities, and the main living/dining area is shared by all, including the Ewen-Smiths. Bev has an office adjoining the house where he has a PC which he makes available to guests who wish to use it for processing CCD images. We soon made ourselves at home in the north apartment. This had two bedrooms, each with twin beds, and a toilet/shower room. Each of the bedrooms had a door leading to the wonderfully large balcony area where the children could safely play. As it was late we settled down for the night in anticipation of the sunny days and dark nights to follow.
The following day we sat down to a continental breakfast and met the other guests, a retired couple from the Lake District. After breakfast Bev showed me the astronomical facilities at COAA. There are two 300 mm f5 Newtonian reflectors: one is on a driven equatorial mount housed in a permanent dome and the other is a Dobsonian which can be placed on one of two paved and levelled circles adjacent to the dome. A third telescope, a 100 mm refractor on a Super-Polaris mount, can also be placed on one of the paved circles and can be used for piggy-back photography or conventional observing. COAA has clear views of the horizon from the north east round through east, south, west and nearly to the north west, with slightly less sky available in the remainder. The southern horizon is 15° lower then in central Britain, so many objects not visible from home can be seen. Light pollution is low, but unfortunately increasing year by year.
The proportion of clear nights at COAA is very high, and it is unusual to have a week without at least one or two good nights suitable for observing. Unfortunately, our first week was unusual and I only managed to capture two CCD images through broken cloud in seven nights! The weather gradually worsened towards the end of the first week and we began to feel increasingly disappointed. In the Algarve, because of the predominantly good weather, life is conducted almost entirely in the open air and, when it rains, there is very little to do. Janet was keeping the children cheerful by leaving little treats for them every day, while Bev was trying hard to make his satellite weather pictures show some encouragement, but it all looked very gloomy. We were all but ready to give up, cut our losses and come home when, on the eighth day, we awoke to glorious blue skies and dazzling sunshine. The Algarve is transformed into a wonderful glowing place when the sun shines!
Thankfully the good weather lasted for the rest of our holiday and I was able to fully test the prototype CCD camera as I had intended. Unfortunately I had the Moon to contend with in the second week but this did not prove to be too obtrusive, as you can see from the images to the right. I captured the images from the camera electronics via the Centronics printer port on a laptop PC. At first Bev and I had a little trouble focussing the camera due to the mounting. With this overcome we soon settled into a smooth pattern of "focus-aim-shoot". I have to thank Bev very much for his excellent knowledge of the sky, his brilliant ability to find and centre objects in the telescope, and his patient guiding of the scope while I operated the computer. I later processed the images on Bev's desktop PC (which was much faster than the laptop I had taken). Bev took a great interest in the image processing and, with a little help from me and the book by Christian Buil1, he wrote a program to deconvolve my images. The two sets of images of M57 and M5 show most strikingly the improvement provided by deconvolution.
Despite the first dreadful week the holiday was a great success both for sun lovers, and for those bathing in the glories of more distant stars!
[1]
Christian Buil, Construction And Use Of An Astronomical CCD Camera, Willmann-Bell, Inc., 1991.
Roy Gooding, Alan Smith & Ian Swann