Observatory construction
This page constitutes an account of the construction of my observatory in the eastern part of Scania, southern Sweden. I will add new information as it becomes available. Please scroll down for latest additions.

animation

Latest update: 2011-Aug-17. Installation complete and first light!

Background

Light pollution was on the increase in our home town of Dalby due to continual building expansion plans and a non-existent lighting policy. Simultaneously we discussed selling the house in Dalby and relocating to nearby Lund or Malmö while trying to find a summer house in the countryside. As it happens by pure chance (almost...) we found a property at one of the darkest places in Scania. We bought the property and relocated to Lund in August 2010. This of course sparked the idea of building a personal observatory at the new site. Promising indeed, but a reality check showed the night sky darkness in Scania unfortunately never reaches very favorable levels due to heavy population in the area. The best we can expect is a visual limiting magnitude of about 5.5. Good, but not exceptional. Still. the project was started in the summer of 2010. (As a side note I have bought a Unihedron Sky Quality Meter and expect to get some real in situ measurements during the coming months.)

I had the following requirements from the beginning:

  • The observatory should be fully automated with remote control support
  • Set-up and tear-down times shall be minimized
  • My current NexStar 11 GPS scope shall be used as main instrument
  • The system shall be optimized for imaging in NX 11 prime focus with option for piggyback imaging with my existing Canon lenses

A short list, but with considerable implications.

The first two items are related and refers to the weather situation in Scania, which is not the least ideal from an astronomical point of view. It is important to be able to exploit any clear weather on short notice. This implies a high degree of automation and remote control, both locally from a warm room and externally from our home in Lund.

The above in turn implied I had to replace my modified Canon 20Da DSLR as main camera since it would be possible but messy to automate and control remotely. So now I was in the market for a CCD camera. Further, since I planned to use my old NX 11 GPS scope I would need equip this with remote focus. Enter computer controlled focusing system.

The main imaging configuration would be prime focus which prompted optimization of this mode to fully exploit the CCD capabilities. I already used the Celestron f6.3 reducer/corrector but the "correcting" properties of that lens is quite limited. In particular there is significant residual field curvature. I wanted to do something to address this. Enter new SCT corrector lens.

I would of course also need a housing for the telescope. Enter automated dome system.

Equipment

To make a long story short, my research into the CCD camera domain pointed me in the direction of the cameras from QSI imaging. I settled for QSI 583 wsg. The main deciding factors were:

  • Integrated front-of-filters guiding capability
  • Integrated five-position filter wheel
  • Capable 8.3MP sensor with multiple binning options
  • Possible to mount Canon DSLR lenses
  • Low-noise electronics
  • Competitive price

I could then use my old Meade DSI camera as guider in the prime focus setup. In this mode I would bin the sensor 2x2 or 3x3 in order to match pixel scale to the expected seeing at my site. In piggyback mode, I would replace the "wsg" camera cover with a "ws" cover because Canon lenses cannot reach infinity focus with the guider port installed. This should not be a major problem since I would use the main telescope as guider scope anyway. I fitted the filter wheel with an Astrodon 2:nd generation LRGB set. For the fifth position I opted for a photometric V filter. I will use 31mm filters in special inserts instead of the standard 1.25 inch mountings in order to use my 200 mm f2.8 Canon lens without significant vignetting.

Now for prime focus focusing, I settled on the NGF-XTcM 3" motorized focuser from JMI. It has good lifting capability and is widely supported by software packages from many vendors.

The matter of reducing the SCT prime focus field curvature was a somewhat more complicated issue. I knew that Optec had designed a corrector lens for the Meade 16" SCT. I got in contact with Jeff Dickerman at Optec and he was very helpful. (Thanks Jeff!) He told me they had recently designed a f8.6 special version of the Meade reducer for the Celestron 14 OTA dubbed "NGC 314". He also showed me very impressive test images from Paul Luckas in Australia. They showed a very flat field over a 50mm diameter focal plane. Since the C14 has the same light baffle output port size as the C11 OTA, the NGC 314 should work for my scope also. But as Jeff told me, they had no test results specifically from the C11 and I should expect some vignetting because the lens system really requires a 3" exit pupil and the C14 and C11 only have 53mm (2.1 inch) or thereabouts. But looking at Paul's results lead me to believe I would only suffer about 20% light drop off for the relatively small sensor I will use (18mm diagonal for the QSI camera). Anyway, I ended up with a NGC 314 and mating adapters for the QSI camera as well as my old Canon DSLR. Since the lens barrel is 3", it was a good fit with the JMI focuser. This should enable me to get RC-type image quality for a fraction of the price, albeit with some degree of vignetting. Time will tell....

For the dome housing I became very interested in the new products from the ScopeDome folks in Poland. They are offering a 3 meter (and recently also a 5-meter) , fully automated dome for a very attractive price. All is included to enable full remote control with ASCOM compatible drivers. I had previously looked into e.g. the Astro Haven clamshell solutions. I really consider these a superior solution to a traditional dome but the price point for an automated solution was prohibitive. Therefore I obtained a ScopeDome from the Swedish reseller Astro Sweden AB and got it delivered during the summer of 2010.

Construction

For the observatory layout I planned to construct a 5x5m wooden deck with a concrete pillar for the scope. The dome would stand on the deck and the pillar and hence telescope would be isolated from the movements of the dome. I managed to get my partner to agree to place the setup on the highest point of the property.

I must take this opportunity to stress that none of this would have been possible without the continual understanding and support from my partner Annie. She indeed deserves cudos for having the patience to put up with me and my hobby which requires both time and some financial input. I would be lost without you!

The image below shows Annie at the site. We have just started laying the foundations for the deck. (Click on images for a larger version.)

Observatory site

The next phase of deck construction was to pour concrete for all of the supports for the deck itself. After that, I fixed the frame and put in the major support beams.

Deck construction

Next, I began to fit the crossbeams.

Deck construction

Now, this was about as far as I could get before pouring the telescope pillar. I wanted to place it due south of the future dome center point in order to be able to get a free zenith view with the telescope as well as piggyback instruments. Some calculations showed I could place the pier center 60 cm south of the dome center to accomplish this and still not run into the dome with the scope dew shield. I had mixed the concrete for the deck supports by hand but the pier would require about 30 bags of concrete at 25 kg's each. This meant I had to borrow a concrete mixer and the image below shows the operation in progress.

Deck construction

I dug an about 0.5x0.5 and 1 meter deep hole for the pillar. The plan was to fill the first 0.5 meter with reinforced concrete and top off with a 0.4x0.4x0.5 meter pillar in which the stainless steel rods for the pier would be inserted. I made a form from some scrap plywood I had lying around. The image below shows the form with a lid holding the steel rods in the correct position for the pier base plate.

Pillar form

And putting the lid on we get the following configuration.

Pillar form

I poured the base concrete and after that I put the pillar form in the correct position as shown below, i.e. 60 cm due south of the future dome center. Note the string marking the North-South line which I had previously marked with the help of a compass. Hopefully this will get me near enough to make the final adjustments with the pillar itself.

After putting in the rebar for the pillar I had to wait for the concrete to cure somewhat in order to stabilize things before pouring the pillar. Time for lunch!

Pillar with rebar

The end result after pouring all of the concrete and putting in the steel rod template is shown below. I added some weight to ensure a tight fit between lid and sides.

Pillar base curing

This would be a good time to take a look at the dome parts which arrived previously.

The dome package was delivered directly from the factory in Poland by truck. It was neatly packaged and all parts was contained within the side panels as shown below.

Scopedome delivery

It was very easy to assemble the basic parts. There are six major fiberglass panels and one box with cabling, electronics, bolts etc. Everything included. Very neat. The image below shows the situation after I had mated the rear and front parts with the sides. Lying on the grass in from of the dome is (from right to left) shutter panel, shields for the rotation cog drive, back door panel and base roller segments.

Dome parts

Front view before installation of door panel.

front of dome

Front view after installation of door panel.

front of dome

Back side with door closed. The door has two locks with keys.

back of dome

Back side with door open.

back of dome

Side view of the dome.

dome side view

After completing the pillar I could finish the deck crossbars. Time to start with flooring!

Deck

Closeup view of the pillar.

Pillar

Decking complete with dome base ring! The yellow tubing at the right is for power connection to the main house.

Completed deck

This is view of the base ring along the north-south line. The picture was taken due north of the pillar.

Base ring

Together with Annie and friends from Societas Coronae Borealis we managed to lift the dome and put it on the deck. We were relieved to find it actually did fit on the base ring.

This is Stefan posing after a work well done.

Dome

Dome

Back of dome with door after fitting of the shutter.

Dome

Front side with shutter partly open.

Open dome

I finally got the pier and it did fit to the pillar bolt pattern! This image below shows the view from the front with my the telscope fitted to the pier. The top part of the pillar is adjustable for azimuth and elevation (see detail image below).

Front

The view from the door opening.

Back

A detail showing the pillar bolts attaching the pier to the foundation.

Pier

A detail showing one of four adjustable bolts between the upper and base part of the pillar. The oblong bolt holes in the top part makes it possible to adjust in azimuth and the nuts allows for elevation adjustments. Next step: Polar alignment!

PIer

Winter is here with a lot of snow. See below for a view of the dome this weekend (Dec 3).

The dome in winter

I have spent the summer vacation of 2011 completing the observatory and I have taken the first light image, a 10 second exposure of M57, below.

M57

Here is the control computer (Eee PC) which controls dome, CCD cameras, focuser and the telescope. I run TightVNC to enable remote control of the complete setup. The computer is also connected to a USB controlled power distributor which enables me to remote reboot the main dome electronics boxes (visible in the background).

Compute

A closer view of the main dome control box.

USB box

The power distribution box on the moving part of the dome.

Connector box

One of four IP cameras mounted in the dome. This enables me to have a good view of the telescope at all times. One of the cameras also automatically uploads images to astronomy.se once/minute.

Camera

A view of the main QSI CCD and the Meade DSI guide camera mounted on the JMI focuser setup.

ccd

The dome from outside. At the top of the telescope you can see one of the IP cameras mounted to see the same part of the sky as the imaging CCD.

Dome