near Wiston in West Sussex
One of the major problems with astro-photography is the time it takes to set up the equipment for an imaging session. The larger the telescope, the longer it all takes. All too often, I have spent up to 40 minutes setting up, Polar aligning, connecting cables and firing up software only to find that the clouds have rolled in and it has all been in vain! The net result of this is that I end up using my simple 'grab and go' system and leave my real kit inside. This is ridiculous, all that investment sitting idle so I decided to look into building an observatory so that I could have my system set up ready for almost instantaneous use whenever there is a break in the cloud cover! The following is a report of my progress.
I have considered the two main types, 'roll off roof' and 'rotating dome' and have decided that the latter would be the most useful for my purposes because of the additional protection from the elements and obstruction of stray light afforded by it's design. The choice now is whether to build my own from scratch of install a commercially available version. Although I have no doubt that I could design and construct my own, time constraints have led me to purchase a simple commercial design which I will then modify to suit my exact requirements thereby allowing me to get on imaging quickly and giving me time to determine the changes that I want to incorporate once any limitations have been found in use.
The cost of commercially available domes varies enormously and as my requirements are pretty modest, I have chosen a 7 foot Dome manufactured by Pulsar of Cambridge, the company who quite coincidentally, I have bought most of my astronomy equipment from. This unit is manufactured from glass fibre and is well suited to my 10" Reflector although it will support up to a 12" instrument. Pulsar also offer a fairly reasonably priced Pier and understand the requirements of my EQ6 mount so I will obtain this from them as well.
Following some extensive research on the Internet, I have tracked down a user of this Dome in the New Forest and he has kindly offered to demonstrate it to me and I will be visiting him during July. If I like what I see (and he speaks very highly of the dome he has) then I will probably go ahead and order the dome, pier and GoTo update soon afterwards.
As part of my deliberations, I needed to see what the observatory would look like in my own garden so as part of my 'selling the idea to my wife', I made a composite photograph of our garden and an existing 7 foot dome so that I could show her what it would look like at worst case - i.e. before I had camouflaged it a little with potted plants and some low trellis! I know that I will have to cut the height of the hedge to about 6 foot and may well replace this end of it with fencing to improve my eastern horizon but that was on the cards for this year's garden tidy anyway!
This is how I see it appearing:-
I have seen photographs of the Pulsar Dome but they all seem to have twin fork mounted Schmidt Cassegrain type telescopes installed in them and as I have a Newtonian mounted on a German Equatorial Mount, I needed to check that the dome and dome aperture would be suitable so I produced a scale drawing to show the worst case offset of the telescope with regard to the aperture opening. From this scale drawing, I was able to determine that even at worst case (viewing due South or due North), the dome would be useable with this telescope.
It is vital that the Pier is well installed as much improvement in the stability of the system for astro-photography purposes will be achieved by this simple piece of equipment being solidly placed so I have decided to bolt it to a separate block of concrete from that poured for the dome itself. The pier support concrete will be a 2 foot cube air separated from the rest of the concrete by a gap filled with polystyrene foam. To achieve this, I will pour the Pier base first and once this is cured, I will replace the supporting shuttering with polystyrene sheet and pour the concrete for the rest of the dome to a depth of 5".
I have now had a really close look at the Pulsar 7 foot Dome by kind invitation of the existing owner in the New Forest and have decided that it is exactly what I need so the project is now on.
I will dig the foundations shortly and then order the dome and pier while I am waiting for the concrete to cure completely. I have decided to hold off from the purchase of the SkyScan GoTo upgrade until a later firmware version becomes available as I am a little concerned that there is currently no 'Sync' command.
I have now completed the groundwork for the Observatory and on Friday I will pour the concrete for the Pier. The following shots show the work carried out so far.
The hole for the pier was dug 30" deep by 24" square and shuttering installed
The rest of the base area was cleared and shuttered
Simon and I started mixing the concrete in a cement mixer kindly lent to me by a neighbour and we started the pour for the pier - this went very smoothly indeed and by 10:00 a.m. we were finished!
I have now poured the concrete for the base with much assistance from my sons Simon and Adam but before doing so, I made a polystyrene foam jacket around the pier base. Additionally, I made a small channel that I filled with polystyrene beads and then sandwiched a sheet of plastic membrane over this thus making it impossible for the main base concrete to touch the pier concrete - this worked very well and I now have a total 'air gap' between the two pourings that will ensure that I do not transfer any vibration to the pier as I move around the dome!
Having poured the concrete for the pier, I let it cure for 24 hours and then removed the shuttering. The extended portion of the pier was then clad in polysterene foam sheets. I did this with two layers, the first layer is shown here but the second layer was used to sandwich the polythene sheet that would later help to separate the pier from the dome base. You can just see the polysterene beads that I poured into a channel all round the pier which were then covered in the polythene sheet. This combination of foam sheets, beads and polythene sheets will stop the concrete for the dome base coming into contact with the pier itself.
The concrete base for dome itself
I have two conduits, one for power and the other for data and 'security'. The data link comprising a CAT 5 cable will be for remote operation from my 'warm house' and this conduit will also take my 'security link' - it is a sad statement of the times that I have had to consider theft during my planning stages and this conduit will allow me to interface the dome with my home alarm although it will also have a self contained RF pager as well!!
I intend having the whole system running on 12v so that even if there is a power cut ( great news - less light pollution!! ) I can still image. The 'Mains' power supply will be for charging/conditioning the portable 12v power supply although I will normally run all the 12v systems from a homebrew 15 amp 12v PSU.
For alignment of the Pier, I needed to ascertain the position of the NCP so having found it using my Polar Alignment Scope, I marked it on the pier base in readiness.
The following series of photographs shows the installation including the problems of getting the dome over my neighbour's workshop into final position in my garden! Many thanks to Keith for letting me use his garden and for his help on the day, my youngest son Adam for taking two hours off work to assist and Dave the 'guy from Pulsar' who gave us the confidence to transport the dome over the workshop roof!
The finished dome installation showing the pier in place
I promised my wife that I would make the installation as 'attractive' as possible (bearing in mind it is a large white dome!) and the process of making the dome fit into the garden less obtrusively has started with the laying of a boundary of decorative bricks. This shot shows the 'dry lay' version to make sure that the idea will look OK but the finished lay will have pebbles laid inside the brick surround and then the potted plants can start in earnest!
The pier that I have was designed to take a Meade LX200 mount so I have had an adapter plate made by Pulsar Optical and this is it! The two tapped holes are for the RA adjustment post.
So that I could still easily use the EQ6 tripod for 'away from home' viewing, I made my own RA adjustment post using a 10mm bolt with the head cut off.
This shot shows the 'owls nest' access hole in the North side of the pier to allow the mount to be bolted to the pier/adapter plate.
The 'camouflage' process is now complete with the pebbles and flower pots - mission accomplished to everyone's satisfaction! The two shots below show the finished project (right) alongside the original mockup.