My Telescopes

A chronological list of my projects

Summer 1979: My first effort, an 8" f7 mirror ended in failure when I took a gas blowtorch to the surface of the mirror to warm it up prior to pressing the pitch lap! Two seconds later I was staring down at three useless chunks of glass on the ground.  The moral of this tale is don't cut corners.

1988-9: My second mirror effort, this time a 6" proceeded further and I got to the figuring stage. Unfortunately I had ground the mirror too deep so ended up trying to correct a fairly tricky short focus surface which proved too much in my novice hands and I abandoned the project.

1995: Success at last! I completed a 6" f6 in a hexagonal wooden tube and mounted Dobsonian fashion. The mirror was a bit of a stinker - but first light on the Great Nebula in Orion took my breath away. The moral of this tale, for beginners in particular is don't be afraid to settle for a mirror that may not be too good. It will probably still work and it's better to get a substandard first mirror up and running rather than keep struggling on the polishing stand and maybe give up. Your next mirror will almost certainly be a vast improvement.

1995: After the 6" I quickly started an 8" f6. This went fairly smoothly and turned out to be good mirror. Likewise the wooden tube assembly and Dobsonian mounting were all improved and the end product proved to be a really good telescope.

1996-7: Built my first grinding and polishing machine using a salvaged golf trolley motor for the turntable and a Vauxhall windscreen wiper motor for the stroke-arm. It cost about 30 quid and with it I reground and polished the mirror from my first 6". I later pulled the motor out for something else so it never got used again as it barely had the necessary power to do the 6".

I spent a long time trying to build a motorised fork equatorial mounting for the 8". In many ways it was a good effort but it never really worked quite right.

1998: The fork mounting was abandoned and I put the telescope back on the Dobsonian mounting and built an equatorial platform instead. This was driven by a tangent arm and a salvaged stepper motor, and worked great. Moving to a house with a bigger garden allowed me to build my first proper observatory, with a run-off roof.

1999: I decided I wanted a telescope designed specifically for planetary and lunar observing so I set about building a 10" f5/f30 Dall-Kirkham. Oh boy! this was some job but I managed to complete it. In parallel with this I replaced my run-off roof with a dome, 6' in diameter and made from 1/2" ply ribs covered with a hardboard cladding.

In use the nylon castors for dome rotation have proved too light for the job and really need to be replaced. Still the observatory works fairly well and is still going strong. Not so the telescope: a system like this needs to be top-notch optically and mine simply wasn't. In addition I realised after a fair bit of observing that the telescope was far too limited in application - deep sky objects just could not be observed at all. Still the lunar view through this telescope was incredible, slowly scanning across the surface brought to mind the footage recorded by the Apollo astronauts as they prepared for the first manned landing ( I kid you not!).

Built a scaled up version of the Waineos grinding and polishing machine. I managed to pick up a great geared motor for £50. Originally three-phase, the bloke just stuck a running capacitor on it and it chugs away quite happily at 37rpm. The machine has ground a couple of 6" mirrors and a 10", but the polishing action is poor due to weakness in the mechanical linkage. I'll sort this out eventually. The picture shows the machine after I finally did get round to sorting it out.

early 2000: Did a 6" f5 to hone up my mirror-making skills. I learned from the 10" that going to faster focal ratios means a lot more difficulty in figuring. In addition this project was an experiment in building a small telescope as quickly, easily and cheaply as possible. The square tube and Dob mounting were all fabricated, in a weekend, from Contiboard (melamine covered chipboard) at a total cost of about £15. I star-tested this telescope with a Ronchi grating eyepiece and it proved to be very good, as well as a joy to use.

Sept. 2000: The Dall-Kirkham was dismantled and the mirror refigured to f4.5 for a Newtonian. The D-K's tube assembly was also modified to this end and the telescope is now in operation and performing quite well. The picture below was taken when my friend Jem and I went to Eye in Suffolk in search of darker skies. I had my first ever view of the Veil Nebula in Cygnus using an OIII filter purchased that very day at the Loughton AS Equinox Skycamp.

My chief aim however, has been to construct a computerised altazimuth for this telescope following the brilliant Mel Bartels system. The first time I came across this I thought it was the ultimate in DIY mountings for a Newtonian. I used size 17, 1.8deg/step steppers from Electromail and 289 tooth 6.5" worm gears from Beacon Hill Telescopes. The system is controlled by a second hand Toshiba 486 laptop. I've managed to achieve Goto slews within a 15 degree radius of an initialization star. The first time I accomplished this was incredible. My particular system has its shortcomings, which are entirely mechanical and I am hoping to improve on this. I would really like to rebuild the mounting in metal. We'll see!

Still seeking that planetary telescope I built a 6" long-focus (f9.8) Newtonian.  

Design requirements for a planetary telescope are rather different than those for one intended mainly for deep-sky use. Aperture is less important than good definition and contrast. One way to improve these characteristics in a Newtonian is to use a long focal length. This becomes a severe problem in mounting terms for larger apertures but a 6" should sit quite happily on a German mounting with 1" shafts. The long focus permits the use of a relatively small flat mirror, and by keeping the central obstruction small (~20%) in this way these characteristics are improved. (See here for a detailed treatment of this issue). I did record time on the mirror for this job: rough ground on monday, smoothed (by machine) on tuesday, rest on wednesday, polished and figured on thursday. A long focus mirror is quite tricky because the shadow patterns are so subtle that testing is difficult. The Ronchi method (see mirror testing) was better than Foucault but the curvature of the lines is extremely slight (at least with my 70lines/in grating). Apparently, at this f ratio the mirror could be left spherical and still satisfy the Rayleigh criterion. 

First light was early October 2000, and views of Jupiter and Saturn were good, although the planets were not well placed. Subsequent observing sessions really proved the value of this design for planetary observing. You can check out an observing report using this telescope, and plenty of contributions from others, at Alistair Thomsons excellent 150mm reflector site.

March 2001: I invested in a small lathe (180mm swing, 300mm between centres) to assist in my efforts to work more in metal. Check the Crayford link for details of a motorised alloy focuser I made. Ultimately I would like to venture into alloy casting but I haven't taken the plunge yet.

I ordered an 8" Pyrex blank and expect to get cracking on this shortly, though I've yet to decide on the design details for the tube assembly and mounting. Maybe a Dob, but incorporating fine adjustment controls, or maybe another equatorial platform (these are great and can be made without any special tools) or maybe.....

Sept. 2001: I've now upgraded my lathe to a larger model, which really allows me to do the kind of stuff I want. The 8" is now well underway. The mounting will be a German equatorial fabricated in alloy, with 1" stainless steel shafts. I hope to attach the computerised (Bartels) drives I made for the 10" Dobsonian, though in the short term I may just use a simple geared synchronous motor that I have available. This will sit on a very heavy-duty tripod made from MDF.

Feb. 2002: And the 8in Newtonian is finished at last. The final design has used PVC irrigation pipe for the tube as I was able to get some for free. The mounting uses 1in stainless steel shafts in a novel alloy insert/bushing combination. Other parts of the head use 1in thick alloy plate. The head is attached to a heavy 3in diameter piece of alloy that sits in a large spare bearing I had. The ball race had to be disabled by pouring in some cement as it had quite a lot of play, but the alloy post rotates quite smoothly in the bearing bore for alignment. The tripod is made from multiple layers of 18mm MDF. Counterweights are barbell weights. The Bartels drives from my 10in altaz have been adapted by the addition of some 5:1 gearboxes and ported over to this telescope. This transferability is yet another great feature of this drive system. You can see the white cables which lead to the interface box in the picture. 289 tooth worm gears give a total reduction of 1445:1. Some parts of the tube assembly were fabricated in fibreglass. My motorised Crayford was replaced with a commercial 2in focuser, as the former was designed for visual use and could not adequately support my newly acquired MX516 CCD. Plastic pipe form a neighbours shed clearout proved useful, as I had a salvaged 60mm objective and put them together to make the guidescope. 

In parallel with the this telescope I built new observatory to house it. I've gone back to a run-off roof design, as this makes better use of the smallish space I have. The dome proved far too small (when they say make them at least 10' in diameter then listen!), and after two years the hardboard cladding had started to deteriorate, and the plywood base ring had warped (all lessons for the future though).

November 2002: A few modifications have been made to the 8" including a homemade unit power finder and the replacement of the 60mm guidescope with a 3" Newtonian. The latter has proved quite useful, I built a two-directional mounting bracket for it though this will need some modification as it has turned out to be less than rigid.

In addition I obtained two commercially made telescopes this year. The first was a NexStar 4, intended for taking on trips. I later sold this to finance the purchase of a Tal 100RS refractor. The pic shows the telescope set up for projecting an image of the Sun.

I made several modifications to this telescope. The first was to add a drive to the RA axis. I made a worm gear on the lathe for this. First I calculated the diameter required to achieve 144 teeth. These were cut using an M8 tap, with the blank mounted in the toolpost. The worm itself is just a length of M8 threaded rod held in bearings in a small alloy bracket. The drive is powered by a synchronous motor that I had available. The output on this was 1/5th rpm, but needed to be 1/10th rpm for a 144 tooth gear, so I added a pair of nylon spur gears to achieve the required 1:2 reduction. The second modification was to attach flexible cables to the slow motion drives on the mounting. The original mounting has a 4 degree slow motion facility on both axes, with a large plastic knob attached directly to the drive screws, but this means that for many positions of the telescope these knobs are difficult (and sometimes impossible) to reach when you are positioned at the eyepiece. The cables rectify this problem, though as is often the case with this kind of mechanism they can be a bit unreliable in use (a stiff rod attached via a universal joint is for many a preferred option).

July 2003: In May I decided to build a new observatory. There were two main objectives: the first was size. All three previous observatories were based on a structure that was just 6' x 6'. This meant rather cramped working conditions, and even one other person inside the building was...... intimate to say the least! The new observatory is another run-off roof design, but is now 8' x 8'. This extra space has made a big difference. There is now comfortable working space as well as adequate room for two or even three people.

The second objective was to create a more appealing interior. This was partly achieved through the extra space, but I also clad the inside with OSB (a cheap and very durable wood-chip board) which I painted light green and also threw down some vinyl flooring.

The observatory is a rather novel design. Three of the walls are fixed and full height, with only the South-facing wall being lower to permit viewing lower down in the sky (although I lose a good 15 degrees in altitude thanks to house roofs). So the roof consists of a top and front panel attached together. This is why the rails which carry the roof in the off position are different heights. This is simpler in operation than the design which runs the roof-top off, and the front panel hinges down against the wall. However, how stable this proves remains to be seen!

There has been one drawback though, and this is connected with the roof design. I intended to operate the roof using a homemade winch, at first manually and then motorised later on. However, for a winch to operate effectively the roof structure must be very stable; any flexure or skewing and the winch can't pull it off, especially when the force is applied from one side (the situation is improved if the force is applied centrally but then you wind up with a winch cable right above your head). So for now the roof has to be pushed on and off by hand. The only solution I can see is to make a new roof, but that ain't gonna happen just yet!

On to more cheerful things. I started out just intending to build a new observatory......and ended up replacing the entire telescope! The newbie is a classic Fullerscopes 8.75in Newtonian, the kind of thing I drooled over as a kid. It's about 20 years old, and complete. A beautiful instrument, and now I understand why you sometimes find wanted ads specifically looking for the Fullerscopes MkIII or IV mountings - very simple, but very, very good. I have kept the telescope as original as possible. I had to reluctantly swap in a 2in focuser for the original 1.75in to accomodate CCD. The original focuser was a treat, it was a basic manual rack and pinion, but one knob was for coarse focusing and the other for fine.

Here she is...............

Two other jobs I did on this were only additions. The first was the homemade 60mm guidescope. And of course, the Bartels drives have been moved in. I really like this marriage between the very traditional telescope design and the high tech computer stuff.

In the above pic, starting from bottom left you can just about see the little ancient Toshiba laptop that originally controlled the telescope and is now reserved for field use. Sitting on top of that is the interface box with the three cables (Dec, RA and handset) for telescope control. To the right of these is a very old AMD K6 Desktop which is now used for telescope control. This PC almost got chucked out until someone reminded me that it was the machine I originally built myself back in the early 90's, not the original of course, various upgrades mean that in fact none of the original machine remains. The open laptop to the left of the desktop monitor is used for CCD imaging, SkyMap and so on. These machines, along with another laptop and a new desktop are all wireless networked too. Part of the reason for setting up this home network was to facilitate remote operation of this set up from the bedroom. Lastly, sitting on top of the PC monitor is a black-and-white video monitor for use with a CCTV camera for moon and planetary observing.

Interestingly, this telescope is significantly more powerful than my previous "8in". That telescope in fact had a clear aperture of 7.75in, so was a full inch less in diameter compared to the Fullerscopes. This may not sound much, but light-gathering power is more directly related to surface area rather than diameter, and the Fullerscopes has 22% more surface area! This is significant.

Now, how did I come by this wonderful piece of kit? I came across an old college pal called Steve, from many moons ago, after trawling round for microscopy sites. Steve is doing some incredible stuff in that area but is also interested in astronomy. So after we got reacquainted, he says I can have this telescope for nothing, gratis, free of charge etc. Yipes. My first proper look was at M13, the bright globular cluster in Hercules. It was truly mindblowing. This object just jumped out of the eyepiece at me, and with a little averted vision loads of tiny, sparkling stars could be resolved. Yeah, I know some of you reading this are now thinking, 'yeah, I know what he means'.

Aug 2003: So, what next? I have two things on the books. The first is to move the TAL refractor on to the GEM that I made for the Newtonian. Like the reviews said, the TAL is pretty good optically, but the mount isn't really up to the job. My own job will be ideal though. I want to put it on a tall hollow wooden pier. The pier will have a door in one side, so that the telescope can be stowed inside, along with room for a battery compartment. This should make a good arrangement for storage and transport, as this telescope does not have a permanent home.

And here is Plan B.......

This is a fairly old Pyrex blank, 11.75in diameter by 1.5in thick. This telescope would collect 45% more light than the Fullerscopes! I'm thinking in terms of f5.5 and a fork mounting. But this won't see the light of night, so to speak, until next year at the earliest.

Please check back again, and I always like to hear from people about their projects too.

Sept 2004: well, observing season approaches, but the 11.5 inch (this will be the final clear aperture after bevelling the edge) is nowhere near done. The basic design has changed too. Originally I planned a f5.5 as I thought this would make a good 'compromise' telescope. It should perform fairly well on both planets and deep sky and fit the observatory. Anyway I ended up with a deeper curve than anticipated and am now doing a f4.3-ish. But I'm happy with this as it led to the idea of a dual telescope. Instead of one compromise telescope, we have a larger short focus Newtonian for deep sky, riding tandem with a long-focus 6 inch for the planets. I have built both of these types before, so I know they work. A big project, and right now all that's done is the rough grinding and up to 320 abrasive on the 11.5. Ho-hum.....