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This page gives a few morsels of information to enable visitors to place Ravenshead Observatory on the world map and what is needed to make astronomical imaging a practical proposition. To start with - for non-UK visitors to the site - this is the only map I could find quickly that places Nottinghamshire on the map of England.
Nottinghamshire
The observatory site is located 20 km North of the City of Nottingham, England and it is 6 km South of the town of Mansfield. Ravenshead is near the left centre of the green area shown on the map. The observatory is set in the back yard of our property and is within the area that was once part of the great Sherwood Forest. For avid film-goers, it is only partly true that the men around here still wear tights - and these tend to be football players!! The village of Ravenshead is quite rural but it is increasingly threatened with infill developments. As a result there are fewer trees every year and there is a moderate but increasing level of light pollution from all directions, but most heavy from SE - SW and NE - NW. If I had been around in the 16th century the site would have looked very different. This is Nottingham Castle at that time - I assume taken with the very first Kodak Brownie CCD Camera. I would have put the observatory at the top of the tower on the left of centre! Not much else around in those days...................................
The area is very different now. At 20 km North of Nottingham Castle (which is now mainly re-built and restored) there have been many smaller towns developed - many of them grew to support the lace and mining industries until the late 20th century. At the site of Ravenshead Observatory now the least light pollution is through the directions NE to SE and the sky typically gives around magnitude 3.5-4.5 star visibility. Very occasionally the Milky Way is visible but with variable seeing (air stability). Due to nearby tree heights and the light pollution there is little opportunity to view the sky below 45° altitude and few images taken from this site have been taken when the target has passed the meridian (ie gone past South to the West).
As a concession to the semi-rural nature of the area around Ravenshead, I built this private observatory to simulate a garden summer house and to blend in with the garden setting - in other words I painted it green.
The view below is taken from the South East, looking North West. The equipment in view is currently being used for astro-imaging and is described in the Equipment section of the web site.
The wall supporting the roof rail track of the observatory was built high to shield the telescope from local lights in the house and neighbouring property security lights. The instruments I use can all "see" from about 35° altitude to the zenith - enough to keep above the heaviest light pollution.
The telescope shown here is an Astro-Physics AP155 refractor ie 155mm diameter object glass or 6.1" in old money. The focal ratio is f/7. Whenever I want to change the field of view of my imaging sessions I can add a focal reducer to the AP155 which converts the focal ratio to f/5.3. The AP155 also has a Takahashi FSQ106N astrograph refractor mounted on its back. This has a 106mm object glass and has a focal ratio of f/5.0. This is used when I want to take very wide field images such as the Pleiades image in the FSQ106 Gallery page. The steel pillar supporting the telescope assembly is bolted down to a concrete base about 1 metre deep and 1.5 metres square. The base of the observatory itself is 3.1 x 2.6 metres. Mounted on the telescope (only just visible in this picture) is the digital imaging camera:- an 11 Megapixel Santa Barbara Instrument Group ST-11000M with an integrated ST-237H self-guider guider chip and an 8-position filter wheel for taking RGB colour and narrowband images. I also have the option to use a remote guide camera on the FSQ106 when imaging with the AP155. This set-up works very well.
On top of the pier and the workhorse of the entire setup is an Astro-Physics 1200GTO electronic drive mount. This mounting has been aligned to within 40 arc seconds of the true north celestial pole to allow precise tracking of most celestial objects.
The observatory has a dedicated 800 Mhz PC that controls all the aspects of astronomical imaging. This computer is in turn controlled by a computer from inside the house using a radio link and Windows Remote Desktop. In a normal nights imaging, the only reason to be at the observatory is to roll off the roof and synchronise the telescope precisely on a star. Typically this would take 5 minutes. From that point image target finding, framing on the camera CCD, focusing and imaging sequences are all performed using Windows XP on the observatory PC but then controlled by computer inside the house. To avoid PC disk or monitor damage through damp and cold these are never switched off in winter.
Almost all images are multiple exposures taken sequentially through Red, Green, Blue and Clear filters. At times of poor visibility and/or when the Moon is causing a great deal of sky glow a special filters are used for deep sky imaging. These "see" only Hydrogen Alpha (Ha), Oxygen III and Sulphur II emissions. These filters also have a very narrow band-pass but they are ideal for imaging nebulae and some planetary nebula. The Ha filter is often used to supplement normal RGB images - Ha emission is in the red end of the visible spectrum. The (Ha), R, G, B and unfiltered luminance (except for infra-red) exposures are later combined to produce the full colour images presented in the Gallery on this web site. Special digital image development software is used to do this frame processing once the raw images have been taken and almost always this is some time after the images were taken. In some cases, the images may be taken over a span of many weeks if the weather is poor and multiple long exposures are needed.
For more detailed information about the equipment and astronomical processing used to produce these images, please see the other pages of this web site or use the eMail link below.
Thank you for your interest.
If you would like to contact me for more information - click here: jan.rek@ntlworld.com
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