Telescope Observatory Conversion

Hello to those interested,

My name is Dave and I live in Bristol in the UK. One of my primary hobbies for a number of years now has been 'Deep Space AstroPhotography'. This is a fascinating and extremely challenging hobby which turns quickly into somewhat of an obsession - so what is it exactly ?

Deep Space AstroPhotography is all about taking photographs of all manner of space objects such as galaxies, nebula, clusters and many other deep space object normally invisible to the naked eye. We require an optically very good telescope on a computer controller tracking equatorial mount. We also need some type of camera, some use a standard DSLR. I use dedicated imaging cameras which are sensor deep cooled to around -30C the purpose of this cooling being to minimise accumulated thermal noise generated by very long (up to 30 minute) single exposures. Images are created by taking many single long exposures and then aligning them and stacking them. This stacking is performed in order to improve the signal to noise ratio SNR. In addition to images of the target a whole array of calibration frames is usually taken to characterise both the camera noise and the optical chain. In is common to require many many hours of data in order to produce one single finished image.

Here is link to my Astro Photography website : www.dt-space.co.uk/AstroImages
(click on thumb nail images to enlarge)

Until recently my imaging set up has been portable. So if a nice clear crisp night with good imaging conditions presented itself I would have to take all the gear from my workshop and set it all up out on the patio. The equipment is heavy but delicate not to mention a lot of wiring that needs doing. Once all the gear is assembled I would then have to go through a polar alignment process to line the mount axis up with the Earth's axis of rotation. All in all at least 40 minutes work assuming nothing goes wrong and then of course I would I have then to take it all apart again at some silly time in the morning when everything is covered in frost ! With the unpredictable UK weather conditions would have to be really good for it to be worth all the effort.

What I needed was a much more permanent arrangement where I could be up and running or packed away in less than five minutes with little effort. That way I could take advantage of those nights where only a few hours of good conditions were available.

Luckily I have two buildings in my garden. I have a lovely purpose built workshop, well insulated and warm. I also have a block built shed/outhouse which was begging for an observatory conversion. The subject of this article is to describe the process I went through to convert the block shed into an Astro Imaging observatory.

I hope you enjoy the description - comments and suggestions always more than welcome !

Step 1: The Donor Shed ...

Here is an image of the donor shed :) internally it measures about fourteen feet (4.2m) square. The walls are made from externally rendered block. The roof is tiled but who ever built the shed did not use appropriate timber to support the roof and so it was badly bowing.

My initial thoughts were that the roof was going to have to go and be replaced.

I decided after a lot of thinking, staring at the shed and drinking beer that I needed a new roof with an opening with weatherproof upstanding and a hatch which could be electrically retracted and closed.

This was not going to be a trivial job so before starting to butcher the shed I decided to build a mock up of the hatch opening at the correct angle. Then pop the scope and mount inside the mock up to check for correct clearances and make sure I would actually be able to see the parts of the sky I wanted to image.

There is an image showing the mock up and a series of images showing the telescope sky view inside the mock up.

Step 2: Initial Roof Conversion

Once I had decided on the size of the roof opening I pulled the mock up apart and positioned the square opening actually onto the roof in order to get an idea where I wanted it positioned.

At this point I decided I really didn't want to actually do the roof conversion myself and so sought out a local building company to do the hard graft for me.

I remember when the guy came around to hear my plan. I went through the idea with him and showed him my mock up photos and all the design work I had some so far - he didn't really say to much ....

At the end of my pitch he scratched his head and just said - 'you are a f**king lunatic but I think we can do it'

And so the roof conversion started ! Here are some images of the boys at work and the fruits of their labour.

Step 3: Finished Roof With Covering Hatch

Once the lads had finished the roof conversion they set about building the covering hatch.

Now they built the hatch on the ground in the garden and it was a VERY robust bit of wood work. As they were building it I could see it was going to be very heavy. Once the felting was done it was indeed very very heavy I would say about 100-120kg and there was no way I could even lift it never mind get it up onto the roof.

At this point I hadn't actually paid in full for the job so the builder had little choice but to turn up one Monday morning with five lads and they man handled to up onto the roof and over the upstanding.

I now had a water proof very heavy hatch covering a six foot square opening in my brand new roof.

All credit to the builders they did a fantastic job. The roof construction is very robust and the roof is completely plumb and flat. The hatch fitted perfectly and has never leaked so much as a drop of water no matter what the UK weather throws at it - brilliant job !

Step 4: So Now the Fun Begins ......

Ok the builders were done paid and left - still thinking I was a crack pot but they did say it had been fun !

So now it was over to me .... I had to design a system to retract this massively heavy covering hatch and then once retracted get it back into a closed position. I wanted this done electrically so that in the future I would be able to use remote control & ultimately computer control to automate the opening / closing operation.

There was no way the hatch could be hinged and lifted out of the way it was just too heavy and awkward.

So I decided the way to go was to put the hatch onto wheels and runners and slide it up the roof until fully open and then let gravity roll it back down the roof into a closed position.

Step 5: The Wheels & Brackets for the Hatch

Having decided on the transport mechanism I set about sourcing suitable wheels and brackets to attach the wheels to the side of the hatch.

I spent 'ages' researching different wheels and casters trying to find ones that would take the weight and would also survive outside and exposed.

In the end I decided on a rubber wheel caster type unit that were designed for outdoor use and were relatively inexpensive and widely available from ScrewFix here in the UK. I went for two single caster and a rear double caster per side. The reason for the rear double caster is that with the hatch completely retracted the up slope section of the hatch was actually off the back of the roof be some two feet and so the rear wheels would be under even more load hence the doubling up.

The next thing was the brackets to couple the caster wheels to the sides of the hatch. I went for 75mm stainless steel angle iron. So I bought a section of angle iron from ebay and set about cutting it into sections with my 14 inch circular chop saw.

It was a nightmare - the saw was just not up to the job and after a few cuts it was obvious I was not going to be able to finish the job. Not to mention the dozens of 8mm mounting holes I was going to have to drill - it was going to take me ages and destroy heaven knows how many tools.

Here is a video of my chop saw attempt (bad idea) :

Step 6: Bracket With Wheels Completed !

After making the decision that cutting the brackets and drilling all the holes myself was complete madness I went to a local machine shop literally just up the road - result !

A very nice machine shop owner asked and listen to my project and what I had done with the roof - he said 'you are a complete madman' but sure we can cut your brackets and drill them up for you.

So I left him the stainless steel angle and within three hours he had cut them all perfectly and drilled all the holes perfectly, even ground all the edges making them nice to handle - couldn't believe it, he only charged me £40 cash with the promise that I would send some photos of the finished observatory. For that money I couldn't have even bought the drills and tools never mind how much time it saved me - just fantastic !

Here are image of the finished brackets and with wheel attached.

Step 7: Roof Runners - Lets Get That Hatch Mobile !

OK great I now had a professional set of brackets with wheels attached.

The next thing to think about was what the wheels were going to run on in order to get the hatch to actually be mobile enough to get it up the roof.

I decided on using (yet again) angle iron although this time went for galvanised steel rather than the unworkable stainless. So two lengths were cut on what was left of my chop saw and screwed to the roof using plenty of nasty sticky sealant to stop the holes leaking water.

Here are a few images showing the brackets / wheels fitted to the hatch and the whole lot sitting on the steel runners.

Once the hatch was mobile I started getting a bit concerned - it was so heavy, I couldn't move it even an inch by hand and had to get it up almost six feet of sloping roof. I thought if this thing breaks free when retracted its going to roll under gravity and nothing is going to stop it. My Dad came around and had a look at what I was up to - he said 'you are a bloody nutter - that thing is going to kill someone' ...... bit of an overreaction I thought so ignored his advice to burn it while I still had the chance !

Step 8: OK, So Lets Figure Out How to Move the Beast Hatch !

Right so the hatch was on and mobile but apparently unmovable !

What I needed was some serious pulling power ..... so after looking around went for a 12V 2000 lb winch. The winch was fantastic and came complete with a drum of steel cable and a manual hand switch.

So here was my base plan :

Run steel cables from a common winching point inside the observatory. From this common point the steel cables run up and over a set of pulleys running left and right. Then up over another set of pulleys up through the roof. Then over a third set of pulleys left & right and the cable then down the roof either side of the hatch to finally attach to a steel mounting bar fixed to the front of the hatch.

As the cables exited the roof there needed to be a mechanism to stop water from leaking in through the cable openings. I used two water proof ABS plastic boxes to house the roof external pulleys. Also these pulleys had to be bolted to the felted roof surface and it was clear the load on the pulleys was going to damage the roof felt. So rather than mounting directly I used two steel spreader plates to distribute the downward load on the roof felt.

Bit more detail :

- The steel cable was rated at 2000 kg
- The pulleys are marine specification and rated at an operating load of 350kg
- All apertures for the steel cable lined with 15mm copper tube to act as a load bearing
- The cable on one side fitted with a length adjuster to fine tune length and even out load

I don't want to put too many confusing words here, it is much easier to watch the hatch open & close video !

Hatch open & Close video :

Step 9: Telescope & Mount Installed - Hatch in Action

Once the roof hatch and retract close mechanism was complete I set about installing the telescope mount.

I already had a sturdy telescope tri-legged pier mount but is was not tall enough to reach the hatch opening. So I built three block towers to seat the telescope pier, mount head and ultimately the telescope of choice for that nights photography.

Here is video showing the telescope performing a custom position park and subsequently the hatch closing.

Custom park & hatch close :

Step 10: Wireless H-bridge to Control the Winch

The last stage of the observatory project was to build a wireless high current H-bridge to enable the winch to be controlled using a remote control and ultimately via a PIC based microprocessor control board in turn controlled from the observatory host and resident PC computer.

Video of the H-bridge in action :

Step 11: Conclusion

The conversion and building of my observatory has added a whole new dimension to my enjoyment of deep space Astrophotography !

I can now open the roof and be up and running in about five minutes but more importantly can be packed up and in bed in a similar amount of time without all the protracted cold & late packing up of gear.

Even if there is only a short weather opportunity of an hour or two the observatory makes it worth capturing those illusive photons of light. Also if the weather turns bad fast I am closed and safe in minutes.

The other big advantage is I can take real time to get the mount polar aligned and then not have to go through the procedure every imaging session - this has really helped and improved target tracking.

Hope you enjoyed my observatory conversion posting - any questions or commons more than welcome.

Cheers & clear skies,

Dave