7" f/12 iStar refractor 15: Tube balance weight.

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Sometimes the gods of the stars do smile upon us. Perhaps in compensation for missing the Lunar eclipse: I was searching for a suitable rail on which to have a sliding counterweight. And there it was, hiding under the bench in the shed with two neat brackets all in shining stainless steel. It was once a towel rail, I think, but I have absolutely no recollection of buying it on my endless rounds of the flea markets and charity shops looking for ATM materials. I just needed to curve the "feet" and find a suitable weight which would clear the main tube. A delve in the brass stock bin provided a nice sized stump to be bored and turned to make it tidy. I have a wheel and screw borrowed from another counterweight to allow it to grip the rail securely. A plastic plug will avoid marring the rod and make sliding more pleasant..

The counterweight rail is good length and the weight sufficient to make a difference in the OTA's balance point. I just have to decide where to put it. If I fix it on top of the tube there is a danger I might use it as a lifting handle. Sturdy as it might be, this would probably shorten its useful life. Underneath makes sense if I remove the handle. This will allow the weight to come a lot closer to the focuser. It would then become yet another handle for pointing the telescope. Or, I could fix it between two of the handles.

If I put it in the wrong place it will be more distant from the mounting's counterweights on the declination axis. Which will require some compensation to bring the OTA back into balance around the polar axis. If the weight is fixed too high on the tube it will tend to rotate the OTA when it is being carried. In the end I fixed it below the finder without removing any handles. The problem then was inserting my large hand through the smallest baffle to fit the lock washers and nuts on the inside of the rail post screws. Not quite "blood everywhere" but it required some dexterity to retrieve my hand. There were far too many projecting screws inside the tube holding the handles on. All of which would need removing, with one hand, before I could slide the baffles out to work on the rail screws in the bare tube. The split, lock washers will ensure the counterweight rail doesn't work loose over time. 

 The OTA is already gaining weight rapidly. I haven't tried to weigh it yet because I wanted to have everything fitted first. By "top and bottom" I mean relative to the finder being on the left side of the main tube for comfortable, right eye use.

With the new tube counterweight midway on its rail a check on the new balance point had it at 80:100cm in favour of the objective. Not too bad really but I'd much prefer a midpoint for a nicely "balanced" look when fixed to the mounting. A short "top end" above the mounting rings always looks wrong to my eye. It's as if the OTA has slipped down through the rings while pointing high in the sky. Which probably means I will have to add more weight at the focuser end. It is much easier to balance the tube on the mounting, with the axes unlocked, rather than resting it on a fulcrum bar on the workbench. The OTA tends to want to rotate on its axis to find its natural balance point. Which means the finder and counterweight try to rest on the bench and won't allow the tube to see-saw.

Before I packed in for the night I bridged the OTA on the benches with a stepladder and brought out my old Salter dial scales. The OTA now seems to weigh 17kg or roughly 37lbs complete. Given its size and construction that isn't too bad. [If I were a young muscle builder on steroids!] I'm using rubber faced workman's gloves to ensure a good grip on the smooth tube while I am carrying it about.

In anticipation of using 235mm tube rings I have been routing out plywood packing rings. My cheap plywood circle cutter began to break up at the center pin clamp as I was making practice cuts. So I had to modify the alloy angle and rails device I had made previously. I need to be able to cut circles down to 200mm internally. Which required a concave radius on the piece of alloy angle to bring the center pin close enough to the cutter. A millimeter too much in radius needs a larger external radius on the plywood packing ring. [and vice versa] Otherwise the tube ring would not close sufficiently to clamp the tube firmly. By the time I was finally ready to cut my rings to the desired size it was getting too dark to continue. The weather has been most favourable for working out of doors with daytime temperatures reaching 60F in bright sunshine.

Click on any image for an enlargement.

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7" f/12 iStar refractor 14: Countercell fixing

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Since I used an 8" main tube, with a 7" aperture lens, the cell fixing screws were very close to the tube wall. I bought some long, cross-head screws to go through the cell flange and the birch rings I had previously glued together. The small,  pressed flange on the end of the tube resists the pull of the screws and weight of the objective cell.

I needed a fixed nut, which would not rotate with screw adjustments, so I used a T-nut with one edge sawn off to just clear the main tube. The spikes on the T-nut face are bedded into the plywood ring to further resist rotation. I greased the threads to avoid rusting of the zinc plated steel. The plywood rings still need to be painted to tidy them up. I had hoped to find another 10" saucepan which can be cut off at the base and the bottom bored out to slide over the main tube. This profiled alloy ring would cover the plywood rings and hopefully look like a solid aluminium counter-cell. Not really necessary, of course, but I think it would improve the appearance without adding weight. Not only will it provide decorative weather protection but the ring will resist any expansion or loosening of the plywood rings over time.

The view of and through the iStar objective lens in place on the OTA. The matt black, painted dewshield surrounds the lens and is sandwiched between the lens flange and the plywood rings. This gives the three push screws of the push-pull, lens collimation adjustment something to press against without digging in. The screws might well sink into the surface in the long term if pressing only on the plywood which would alter the collimation.

The lens is completely transparent to the human eye but the apple green anti-reflection coating becomes visible in the camera flash. The dust is also invisible, until caught by the flash, but does no harm.

Two satin chromed, brass, drawer handles and a Skywatcher [?] 9x50 finder are now attached to the OTA. I shall probably add another handle at the focuser end to avoid having to point the telescope by grabbing the focuser. Brass lasts well out of doors while coated steel rusts rapidly. I checked with a magnet in the shop to ensure I didn't buy the rusting kind. The finder and handles only moved the OTA balance point by about an inch towards the focuser. Here the focuser is set to infinity in the middle of its travel with the star diagonal held in place by a 2" extender with compression ring. The focuser rotates smoothly in the back plate. Since the back plate is a tight, friction fit it can be aligned and then radial self-tapping screws used to hold it firmly in place. Otherwise I'd use push pull screws with a leveling plate. I am still considering mass loading the back plate out of sight inside for a better tube balance point.

A sliding balance weight on a bar at the focuser end will help. I am looking for a suitable towel rail as a materials donor for this task. This will further improve the balance without unnecessary ballast. The counterweight can be adjusted for different weights of accessories fitted in the focuser. Such a long OTA is very sensitive to changes in moment arm. I shall add a carrying handle somewhere in the middle when I know where it will clear the tube rings. [Which are on order after sending the last ones back due to cracking.] An 8" diameter main tube is much easier to carry than a 12" but having comfortable carrying handles adds greatly to mobility and security.

The OTA is progressing nicely as it rests on my old folding workbenches. Very handy for holding the tube securely with it resting in the fully open jaws. The G-cramps are extra insurance for when I am frequently rotating the tube to work on it. Handy too as a stand for checking the half-mile distant trees through the eyepiece. Nicely crisp and free of false colour at 74x despite the shimmering thermal effects.

For scale: The 8" diameter, main tube is now 6' long from the back of the dewshield to the focuser back plate. The focal length is a nominal 7'. [7" aperture @ f/12] A handy saucepan lid slides over the dewshield for extra security. Friction fit, insertion-type, lens covers can easily take the matt black paint off the dewshield.

Click on any image for an enlargement.

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7" f/12 iStar refractor 13. First Light!

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Three weeks after ordering through the UK distributor my 7" [180mm] f/12 R35 iStar objective lens has arrived. At first it seemed to be made of lead encased in cast iron. It's remarkable weight totally eclipses my 6" f/8 Synta/Celestron! After several attempts with different scales I made it 4.9kg or 10lbs exactly. The latest spec 7" f/8 is claimed to weigh 4.65kg. I had allowed 5kg for the objective in my balancing experiments so that was close enough.

The term "yard cannon" takes on a whole new meaning at this scale! 10" diameter dewshield, 8" main tube x over 7' long overall.

First light was with a bare 8"x 6'6" tube about 7" too long for focusing with an eyepiece in the Vixen focuser. I had to resort to holding eyepieces in my fingers at the end of the open main tube. Not having any useful tube rings I had to prop the OTA on my stepladders to observe the very low, gibbous moon. Once it cleared the 10' high, eastern hedge the Moon was perfectly placed for such a humble, altazimuth mounting! You couldn't ask for better! Except, perhaps, a set of functioning tube rings and a mounting on which to hang the strangely massive OTA.

Despite the shiny [unpainted zink] of the inside of the main tube the moon looked fine at low powers. I worked my way up from 32mm to a 20mm Meade 4000 Plossl for about 105x before I completely ran out of focus in the depths of the tube. The Moon was nicely white with just a hint of green or magenta on the limb depending whether I was inside or outside of focus. At focus there seemed to be no fringing at all. Though it is far too early to judge anything else at this stage I was impressed with the lack of false colour and the sharpness of the lunar features. There was not the slightest wish for a minus purple filter so typical of my using my 6" f/8. I routinely move the Baader "Fringe Killer" filter from one eyepiece to the next on the f/8. It would have made far more sense to fit a 2" filter to the star diagonal to save all the palaver. 

Most people use a laser collimator but here I was holding eyepieces in my hand like a complete amateur. I lasted a couple of hours before the Moon was no longer at a comfortable angle for stepladder mountings. I also missed the comfort of my 2" dielectric star diagonal!

The first job this morning was to shorten the main tube. By holding up a scrap of paper to focus the moon last night I found the focal plane seemed to be right on the end of the focuser when fully racked in. Wrapping the main tube with a length of lining paper ensured the circumferential pencil line was perfectly square. I decided to cut off 8" when 6" or 7" would probably have done, leaving a tube length of 70". The hacksaw wanted to jam as I progressed around the tube resting on two folding B&D workbenches. The benches have been superb for working safely on the OTA with the jaws wide open. The thought of working on a flat bench with the terrifying risk of the tube [and objective lens] rolling right off onto a concrete floor does not bear thinking about!

Once shortened, I now needed a focuser extension tube to reach focus with an eyepiece when fully racked out! Easily achieved, as I have several 2" extenders in my collection which came free with secondhand focusers purchased online.

BTW: The galvanized, steel tube is very stiff but only 0.6mm thick and comes from Lindab's LRTR complete range of industrial extractor tubing in 2m lengths. Available in sizes from 4" up to at least 12" from memory. This is not the more common spiral tubing but has a neat, flattened, longitudinal seam. The stiffness is probably on a par with 3mm aluminium but marginally lighter. Sawing the end off removed the small flange which I had been hoping to keep for greater radial stiffness. However, once the focuser back plate was pressed firmly into the main tube everything was perfectly stiff again. I am now wondering whether I can find a donor saucepan which will fit snugly over the end of the tube instead of inside it. This would make a much neater job and hide the raw end of the tube. The difficulty is in measuring the inside diameter of the bottom 1" of tapered saucepans, often with decorative spun rings.

I had bought some matt black, blackboard paint on my shopping trip this morning. So I took advantage of today's 60F warmth to paint the inside of the main tube. A long handled, cranked paint brush made short work of the tube paint job as I was easily able to reach the middle from each end. Never pass up a dirt cheap discount offer of paintbrushes at the supermarket.

I also painted the inside of the stumpy dewshield, the baffles and the inside the focuser back plate. One generous coat of T+ was easily sufficient for a nicely black, non-reflective finish. The baffles will do the rest in killing contrast-stealing stray reflections. A perfectionists would probably give everything a second coat to hide the few remaining brush strokes but it will never be seen except by me. I have heard it suggested that adding flour or powdered grout to blackboard paint improves it even more. 

The galvanized exterior of the steel, main tube is surprisingly heat absorbent in even the weakest sunshine. Not an ideal material for a dome one would have thought! Though domed silo tops are occasionally converted for observatory use aluminium is much cooler in sunshine. Once I had finished painting I turned the tube at right angles. I was hoping to soak up the late September, afternoon sunshine to speed the paint drying. Schrinlings T+ blackboard paint is water based and very safe even for children. The far more expensive alternatives at the DIY store contained Zylene. Which had me rather worried what the solvent off-gassing might do to my objective lens or its coatings over an extended period.

The T+ paint went a very long way and had a slight jelly-like consistency which completely avoided the usual drips. The perfect thickness and low odour made it very pleasant indeed to work with. Cleaning my hands and the brushes in water afterwards was completely effortless. So different from the stench of turps and scrubbing to get one's hands clean with the usual oil-based paints, followed by cracked cuticles. The T+ paint dries to a matt finish remarkably quickly [even at a mere 15C, 60F] and is claimed to be waterproof after 48 hours. I may leave re-assembly of the OTA until tomorrow to be sure the paint has fully hardened and released whatever drying agents are involved. I also need to consider how shortening the main tube affects the baffle assembly. The supporting threaded rods are now far too long and moving the nuts along too time consuming to do it twice. I still have my full size drawing to ensure the baffles are arranged correctly.

I used my full size drawing to confirm the placement of the baffles in the shortened tube and cut off the excess of threaded rods. After refitting the objective I double checked the focal plane on the sun. A couple of sunspots suddenly popped into sharp relief. The blackening of the OTA innards and baffles has greatly improved the contrast on distant trees. No sign of the purple wash, which plagues my 6" Synta f/8 on terrestrial subjects, which is very pleasing.

Click on any image for an enlargement.

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7" f/12 iStar refractor 12: Reinventing the wheel!

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The trailer nose wheels have arrived but I have no 10mm x 65mm, galvanized coach bolts in stock.

Galvanized bolts later bought at a builders merchant. The quality was dreadful and I had to try a number of nuts and bolts before I found a reasonable fit. Then they had the temerity to charge me over £1 each!

The next problem is drilling the legs for the wheel jack-post clamps. The pier is so heavy and awkward that it can't be easily set up for accurate drilling. With the box section legs 50mm wide it would be very easy to drill askew. Fortunately the clamps only have two bolt holes each. Some clamps have four corner holes in their base plate which wold have double the work of drilling.

I decided to lean the pier over onto a folding workbench. It was quite a struggle to get it tipped over from upright and then to stop it from crashing down onto the workbench. Once the pier pipe was resting safely on the bench two pier legs remained on the ground for stability. With the third upright and at a comfortable height to be drilled.

I marked the first hole to clear large studs in case I wanted it reuse them for stabilizers. A G-cramp held the clamp base plate firmly to the leg while I worked. Once the first bolt was fitted and tightened I inserted and clamped the jacking post and squared it against the leg with a large try-square. The second hole could then be marked and center punched for drilling. I used 5 drills in stepped sizes up to 10mm for each hole. Drilling goes much more quickly this way than trying to force a large drill straight through from the start.

Once the first clamp was fitted the pier could then be brought back upright, tipped between two more legs and the next leg worked on in turn. The final result was an easily moved pier for the first time since I welded it together. With the correct tire pressures the pier does rock when pushed about. Though it is difficult to say whether this would occur with the telescope in use.

There are puncture free wheels available in this size. [Standard sack-truck size.] Which would be considerably more stable but tend to dig in more on soft grass. I fitted puncture free wheels to the garden wheelbarrows and quickly discovered their firmness. Nor do the solid foam tires roll so effortlessly as the pneumatic variety. The great advantage is, of course, a complete freedom from punctures when our tall hawthorn and blackthorn hedges have to be clipped.

If the pier legs were longer I could have added jacking stabilizers but there is not much room when the trailer wheels have to castor to allow free movement in any direction. Fitting clamps and jacks inboard of the wheels would  make rather a small triangle. While moving the wheels inboard of jacks would make the pier much more unstable when being moved about. The stabilizing jacks use the same 48mm clamp size as the wheels.

The images shows the trailer nose wheels fitted with a considerable gain in pier height over the old castors. Handy for ground clearance when viewing near the zenith.  I shall have to clearly mark the jack posts to achieve an average height before jacking up the pier. Even in daylight it is difficult to judge. I shall also have to dismantle the jacks and grease the threads since they seem rather stiff. The wheel's roller bearings were not lubricated either when I removed a wheel to gain better access to the valve.

The temporary 8" tube rings are simple alloy straps to allow me to hang the tube while I wait for new rings to arrive.  It started raining just as I finished so I had to put the tools away in a hurry. So there was no chance to take any more images.

I shall have to consider the pros and cons of different types of storage. If the OTA could be permanently mounted it would greatly increase the chance of observation under a clearing sky. The sheer inertia of lifting a heavy OTA onto the high mounting has always been a huge hurdle to observing on a sudden whim. Even worse was the thought of getting it back down again when it was wet with dew or covered in a film of ice or white frost.

Short of a lottery win, a suitably large, commercial dome is completely out of the question. The latest Pulsar 3.5m dome costs somewhere around £7k by the time it is delivered and erected on a suitable observatory wall or flat-roofed building.

I have often considered a [semi-cylindrical] rotating, barrel-roofed plywood "dome" as ideal for a long refractor. The gentle bending radius of the roof is easily within the range of 4 or 6mm BWP birch plywood. Though the "dome's" finished weight would probably require a good number of skate wheels to support it with low enough rotational friction.  The inertia might prove a  burden for manual rotation. Aluminium would be much lighter but I have no idea where to obtain enough material for a 10' x 10' half cylinder at low cost. A half cylinder would require at least four 8'x4' sheets of material plus the shutter materials and two semicircular ends. 

I suffered from years of shoulder pain due to industrial repetitive strain injury. This severely hampered my ability to lift anything above shoulder height. Nor do stepladders lend themselves to loading an OTA onto a high mounting. The stepladders always gets in the way of the pier or its legs however they are arranged. Climbing  the ladder without a free hand requires the balancing skills of an acrobat. Metal, U-shaped drawer handles greatly reduce the risk of dropping the OTA but do not make it any lighter. Nor less cumbersome while climbing a ladder.

Click on any image for an enlargement.

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7" f/12 iStar refractor 11: Curing that sinking feeling.

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After endless struggling to move my welded pier around the lawn I suddenly had a new idea. The small, solid tired, castors which I had been using sank far too easily into the soft lawn.

Then I noticed the nose [or jockey] wheel on my trailer. A local discount store sells complete nose wheel assemblies including the fixing clamps and the screw jack posts. I just need to fix a jockey wheel clamp to each leg of my massive steel pier and I shall have the mobility I have been seeking for years.

Leveling, raising and lowering can be all be easily achieved with a spin of the handles on the screw jacks. Locking of the wheels, if necessary, is easily done. The screw jacks allow a considerable change in pier height as the tubular body is allowed to slide through the clamp. Once jacked up with the screw, the leg can rest on a lump of timber to allow the jack to be rewound and then slid down through the clamp. Once the clamp is re-locked the screw jack can lift the pier off the timber props for even more height. Ideal when viewing high overhead to avoid muddy knees. When viewing at lower altitudes the pier height can be just as easily lowered again to avoid climbing a stepladder. 

The wheels turn and castor freely to allow rapid changes in direction in a confined space. Handy for rough polar alignment.  The 260x85 [10" x3.5"] pneumatic tires have 150kg capacity. Each well beyond the weight of the complete instrument.

I revisited the rotating focuser to remove the slack. There were a couple of burrs left on the back plate cut-out which were easily sanded away. Re-assembly resulted in smooth, slop free rotation.

I shall need to fix the 8 x 50 finder support stalk directly to the main tube. When the dovetail was fitted to the focuser slot the finder was physically blocked by the 8" [20cm] back plate diameter.

I have cleaned the algae from the pier. The dark blue Hammerite paint has lasted remarkably well considering it has been standing out of doors and exposed to the weather for years. A scrub with a washing up brush and a little washing up liquid quickly cleaned back to the paint. I am uncertain whether I want to repaint it in another Hammerite colour or leave it as it is. The Fullerscopes MkIV mounting could also do with a repaint. Which leaves me wide open to a complete update in appearance. Many modern mountings are often light coloured. Though I rather an favour overall grey as a tribute to famous, classical refractors from Clarke and Cooke. Lighter coloured pier legs/feet would certainly be far more visible in the dark. Though the shiny plated surface of the wheel jacks should help to make them much more visible.

After searching for details on repainting old Hammerite I discovered that its properties had changed dramatically since environmental and safety issues had altered its original ingredients. Opinions on a boating forum were very negative about the more recent product on rust protection of their highly vulnerable trailers.  

I would also like to arrange control rods for the slow motion axis locks/drive engagement. The original "radio" control knobs are often difficult to find in the dark and are sure to become harder to reach due to increased pier height. Most classical refractors had long control rods coming right back to the eyepiece to allow the observer to easily make such adjustments. Connection will require flexibility or universal joints to be connected to the present short stalks on the mounting.

The Fullerscopes MkIV uses a threaded rod [stud] to press a nylon plug against the inside of each, ring-like wormwheel. This locks the shafts by using the worm itself to deny rotation to the 6" 359t wormwheels. Because the locking takes place between the castings and wormwheels it simultaneously engages the drives if the synchronous electric motors are actually running. Not quite on a par with a dedicated screw down friction lock [MkIII] or circumferential clamps. The worms can slip against the very fine wormwheel "teeth." This can most easily occur under conditions of serious imbalance and should not be automatically trusted without some prior thought.

Having much easier mobility for the entire instrument opens up the distinct possibility of parking it under a secure, overhanging structure. Provided it is sheltered but not tightly covered the birds should stay away. The excellent weather proofing, wind shelter and security from predators seems to make protective tarpaulins act as bird magnets.

Click on any image for an enlargement.

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Fullerscopes MkIV in primer on eBay 25th March 2015

I missed this auction despite having a Fullerscopes "saved search" on eBay[UK]

Sellers text:

"Selling a MKIV Fullerscopes mount. 

It is at the moment in original powder crackle finish but am repainting grey primer. so revised photos to follow.

RA and Dec axis mild steel 1.25" shafts are being cleaned up and re greased. RA wheel in good condition, worm may need re working. 

Old spec showed 12" Newtonians with cast aluminium rings so will take newer 14" scopes, very sturdy mount capable of excellent tracking, easily fitted with AWR goto.

Includes Pier base as shown and 1 x 10Kg counterweight

For clarification.  The first two photos show the mount on a short pier/pipe so that i could photograph and this is not included. 

The third photo shows the parts of the mount that includes a stand off plate that allows you to mount the MKIV to your own pier.

Pick up Fareham or can courier at cost. Pier not included"

 The MkIV looks almost modern with a light coloured finish.




Stand-offs to raise the mounting base from the pier top plate. An idea I might copy myself. 

A 6" slow motion worm and wormwheel set.

The MkIV wormwheel had 359 teeth.

This is a later, fully enclosed worm and housing.

The auction finished on £125 after only one bid.

Click on any image for an enlargement. 

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Video of MkIV with Goto!

Here is a MkIV which has been converted to Goto with belt drive.

 

Published on 10 Sep 2015

Conversion of a old Fullerscope (ca. 1970) with Servo's and new Encoder for use as GOTO. Unfortunately, the RA axe is bent at the end, but the Mount (about 30Kg) runs very well. Carrying capacity is 50kg. Video runs about 8x faster. The decl. makes 1 revolution in 60 seconds, Servo is only 8 x 3 cm with a gearbox 1:80

7" f/12 iStar refractor 10: When is an observatory not...?

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When it can't see the sky?

Here is another random, scatterbrained discussion of my difficulties in overcoming a lack of clear sky. Our house runs along the southern border of our rural property. There is a shelter belt of trees to our west. The northern and western  borders of our garden are also wooded for all intents and purposes. Our eastern border has an 8' hedge and another 8'+ hedge on the far side only a few yards away. Lifting myself and my telescope by 8' from the ground gives a remarkably improved view of the sky except to the north and west. The lower altitudes are hardly worth having anyway due to much poorer seeing. I have always tended to set up on the parking area north of the house. Several large trees stole my view from the main lawn over the years as they rose by at least 20'.

I am still struggling with the problem of improving the OTA balance point while avoiding adding unwanted mass at the focuser end. Observatory telescopes often have added weights but I am not supposed to be building such an instrument. This OTA is supposed to be light enough to be fitted and removed from the hinged mounting rings by one person. Recently, I watched three men, lifting, moving and mounting a modern, commercial, 8" refractor OTA on a YouTube video. Whoah! I am past retirement age and would be working entirely alone under much more difficult conditions!

What about a crane? A boat winch attached to a simple frame built rather like a garden swing? It need not be very heavy but could have wheels to bring the OTA to the mounting. Except that a fixed mounting is so limiting down at ground level.

I could make a waterproof "roof" for the complete telescope but worry about rapid deterioration. A lens cap would keep the worst of the weather off the precious objective. While the OTA rests horizontally and permanently on its mounting under its minimalist cover. But! I already have birds nesting in the MkIV mounting under its closely wrapped and tightly secured tarpaulin! Imagine what the little devils could get up to with a bare telescope tube under a simple cover? There would be standing room only! How is this supposed cover to be supported? How light can it be made? Who will lift it down? How will it survive a wind storm or heavy snow? A steeply pitched, A-frame shelter could be wheeled away from the complete telescope on its mounting. Back to the poor, sky visibility, ground based telescope problem.

A number of secure outdoor "cupboard" options occur to me but these would still require extracting and lifting the heavy and cumbersome OTA onto the high mounting. And, taking it back down again when I am tired. Probably in the early hours of the morning when it is pitch dark and the telescope is quite literally sheathed in ice. I thought of a series of hooks or lipped shelves to be fixed to each rung of a builder's stepladder. The OTA could be lifted and lowered in small, secure steps while kept safely horizontal. I could rest at any point in the manhandling of the OTA. The difficulty is in raising myself to match the present height of the OTA so tat I am not lifting overhead.

A carport or garage would offer decent cover and weather protection but I don't have a carport. There is plenty of room for one but it would add considerably to the expense. Though the raised platform idea is not impossible if built with DIY skills rather than a commercial kit. All of which leaves me torn between several, completely conflicting choices.

I would much rather be observing from the roof of this non-existent carport. Which automatically demands some kind of totally weatherproof cover for the telescope since it cannot be taken up and brought down again between observations.

Say I built a platform in front of the shed's southerly gable end. The existing shed could even have rails bolted to the roof to allow a similarly pitched, lightweight roof to roll back to uncover the instrument. Except that the rolling roof would be far too low to cover a refractor on a platform on an even taller pier. A steeper pitched, roll-off roof would add a little extra clearance height but might then act as a sail. Let's not forget about building that sky-scraping pier while we are pondering this option.

A telescope cover always assumes it is easily removable to allow whole sky views. Isn't that what is usually known as an observatory? Do you know any carports which have a huge pier right in the middle? The pier would make a mockery of my already limited parking skills. Build the pier in the unused space between two adjoining carports? Yeah, right! Let's double the expense!

Climbing stepladders on a raised platform to fit a recalcitrant tarpaulin? You are joking? It is already a struggle to cover the mounting on its pier at ground level using a sturdy builder's stepladder for support! Now add the spinnaker required to cover a 7' long telescope on that same, 8' tall mounting. With all of the above raised on an open platform without the protection of our own, soaring hedges.

Something to house a 7' long instrument [with added 2' dewshield] preferably needs completely safe standing and sitting room for the observer on all sides. All of this raised high above the ground? What about that incredibly tall and massive pier? Something solid enough to support the telescope and mounting free of the platform and the inevitable tremors that is somewhere around 16' high? What about that "something" which can protect the telescope permanently from the weather. Yet allow rapid access without my lifting anything heavy nor risking my life?

Better surely to move the whole instrument on large pneumatic wheels on the ground? Wheels which can carry and move the load regardless of the firmness and flatness of the ground? [Snow, ice, soft gravel, soggy lawn, wheel tracks and melting permafrost.] Wheel the instrument to positions in [and out of] the garden where more of the sky can be seen. The fat tyres are easily firm enough to ignore telescope movements and a modest wind.

What about screening from several neighbour's comfort blanket "security" lights and passing traffic headlights? It's much like the contact scenes from Close Encounters around here in winter. With those blindingly bright strips of "landing lights" left on all night just in case. I kid you not!

I could build huge castors with the wide, 40cm/16" pneumatic wheels which I already own. These would automatically provide an altitude boost depending on their exact design. In fact, only a single wheel actually needs to be castored to allow steering.  There would then be no need to build a massive wheelbarrow, or cart, to move the pier around.

Building a practical cart has already proved far more difficult than I ever imagined after wasting a whole morning with a stack of 8' lengths of slotted angle iron. The sheer effort required to lift and move the pier with such a contraption easily outweighs any possible advantages. The same would hold true for a converted car trailer chassis. The ground is not level and landscaping to make it level is not remotely an option. Think in terms of contractor's digging machines and lorry loads of imported sand or soil. It's just not going to happen.

The cost and disruption of covering the entire garden in concrete slabs, to allow easier movement on the existing castors, is a complete non-starter. Rails are similarly out of the question. The area to be covered would require much of the garden, parking space and drive be turned into a paved surface. It would require attacking the existing trees and tall hedges just to be able to move the whole pier and its telescope freely around. If I cut down all our own trees and hedges the neighbour's obscuring greenery, and adjoining small "forest," would still be there.

Building a platform in front of the house would expose it to gales, the neighbour's overkill security lights and very public view. Not an option I really favour for all of the above reasons. Though it would gain much more southerly sky despite the high, shelter hedge. This forward position has already been vetoed by the constant gardener.

I could build a temporary scaffolding platform in front of the shed but am unsure how to source such material. Aluminium scaffolding towers are ridiculously expensive and have very small working platforms anyway. Perhaps a few 4"x4" pressure treated posts and some joists and planks is the best answer? Though still leaves me with the problem of the tall pier.

Old TV lattice masts might be the answer here. There is a steady trade in old and new masts in Denmark. Being self-standing [on concrete foundations] avoids the need for guy-lines, massive concrete castings or triangulation. Getting them home might be the biggest problem apart from the weight. They are far too long to simply put on a car trailer. I have sourced an unused mast not far away at an acceptable price but fear the huge effort in setting it up vertically and keeping it that way. These things are deliberately massive, galvanized, solid steel bar and intended to last for many decades without safety issues.

I [we] could move to another house with far better access to the sky. Except that we are in the middle of a continuing housing recession in rural Denmark. The banks aren't lending all that taxpayer's bail-out money to anybody. Least of all the already retired with no capital and a lingering mortgage. Houses locally have been sitting on the market for years as their estate agent's signs slowly faded to illegibility. There is no reason to suppose anything will change soon. Nor that our own particular "des res" enjoys any greater sales potential than any of the others.

These unsalable homes usually end up on forced auction, even being abandoned or demolished. So that the area becomes an eyesore and drags other local houses further down into the mire. So a quick sale and purchasing elsewhere is as likely as all existing hens growing a smart set of teeth overnight. There is even political talk about dumping the ongoing masses of refugees into empty rural housing. Except that most refugees aren't stopping here but going straight on to Sweden and beyond. They have probably heard about the cost of living here!   

Click on any image for an enlargement.

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7" f/12 iStar refractor 9: Baffling.

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It took several hours to make and assemble five baffles neatly from thin, aluminium, flashing material. I marked all the circles out first with compasses and then cut out the circumferences with metal shears. Then I bored the centers to 12mm and spun them each on the lathe to mark out the apertures. Finally I cut around these slightly indented marks with a jeweler's saw. My hope was that the indented rings would act as knife-edge baffles leaning towards the objective. However, the thin metal was far too flexible to allow much depth of cut. In retrospect it might have been better to try and find some slightly thicker raw material. 

A little de-burring with an oval file and I was almost done. Except for drilling the pre-marked and center-punched holes for the studding. These were to hold them at the correct distance from each other and relative to the objective. Because of the fine thread it takes ages to run M4 nuts along the screwed rods! So I used a rechargeable electric drill to run some of the nuts on near the center of the rods to save time. Then it was just  matter of spacing the baffles at 40cm centers with a tape measure. I rotated duplicate holes in the middle baffle to avoid having to join the rods in line.

The problem is deciding what to to do about the first baffle behind the objective. Should there be a baffle right behind the objective to stop the baffle tree from sliding up and down inside the tube? Or a gap, with nothing at all, but requiring the baffles be fixed at some point? There isn't a lot of metal left after a 7" hole is cut out of an 8" disk. Nor does one want to lose clear aperture. Shifting baffles will risk losing the clear aperture one pays for if they move towards the lens.

The advantage of using screwed rods and nuts is the ability to place the baffles very precisely and to change them later if needed. Plywood baffles glued to wooden dowels requires far greater care in design and assembly. Otherwise they could remain in the wrong place forever.

The images show a rough mock-up and is not the final spacing. Naturally the baffles will be painted flat black to kill reflections. As will the inner surface of the telescope tube. 4mm rods was a good choice for strength and stiffness without adding too much extra weight. The flashing was the only sheet aluminium I could find locally but was ridiculously expensive.

Because the tube is slightly oval I had to make the rings undersized to avoid them jamming. Though I intended to scallop the baffle edges anyway. This is to allow any thermal air currents to flow along the inside wall of the tube. Rather than cascading over each baffle in turn, like a waterfall. Which might well affect the seeing. The scallops will have to be rotated relative to each other, on each succeeding baffle, to avoid direct leakage of stray light along the full length of the OTA.

I was determined to have an all-metal baffle system to avoid the danger of fire should I ever use a Herschel wedge for white light solar observations. The focused heat from the objective passes down the tube when it is aligned on the sun. Plywood baffles might just get a little too warm if the sun should drift off-center. Though I suppose the first baffle will shield the later ones where the most heat is concentrated closer to focus. Full aperture solar foil filters avoid this problem by reflecting the heat away before it reaches the lens.

After having some doubts about my scale drawing I found a roll of lining paper. This allowed me to draw a full size light cone using a 50mm diameter circle of illumination at the focal plane. This very quickly showed that my baffles could not be made to coincide with any likely joining place of the threaded rods. It is quite remarkable how a full scale drawing shows how far a baffle has to be shifted along to avoid vignetting. 

Now I shall have to reduce the circle of illumination to a more normal 30mm or even 25mm diameter. I had used 50mm to allow an SLR to be used at prime focus. I may still make a full aperture baffle to go behind the objective lens to tidy up the rod ends. Though I would rather not for fear of reducing the clear aperture. I wish I had made a full scale drawing first. I would then have the freedom to choose baffle spacing or the aperture of each diaphragm.

Fortunately it turned out just right using 6", 5", 4" & 3" holes in the baffles. Which reminds me I must make the holes into knife edges to avoid grazing incidence reflections off the baffle apertures. This is much more important for thick baffles but even my thin aluminium ones might as well be as perfect as they can be. Any stray reflections will lower contrast by scattering light into the field of view. The advantage of the refractor is the absence of obstructions in the light beam which can spoil other designs.

In the end I chose to use a 1.5" [38mm] diameter circle of illumination. This allowed my original, one inch stepped, baffle apertures with reasonable baffle spacing. Instead of making a thin baffle ring behind the lens I am going to slide the whole baffle assembly towards the focuser. I just need to ensure a fixing to avoid the baffles shifting about over time. Particularly if parked on its nose for compact storage. Having seen a refractor crash to the floor when it rolled off a sideboard I am squeamish about storing refractors horizontally.

I have removed the 3.5" baffle as superfluous but will probably make a 2.25" just to tidy up the rod ends. Anything smaller [like 2"] gets rather too close to the focuser. It may be more sensible to leave the choice of final baffle size and position until I know the exact focal plane with a 2" star diagonal fitted to the focuser.  I could arrange for the baffle rods to be fixed to the focuser back plate. Tiny, 4M exposed Nyloc nuts would look fine in that position. As would bronze or stainless steel, domed nuts. 

Peering into the OTA from the edge of the tube now places the edge of each baffle aperture perfectly in line. Though it is possible to see the inside wall of the tube, the reflection from the blackened surface will blocked by the next baffle along. The threaded rods now overlap considerably though this is not of much importance. Once a final decision is made with the objective lens fitted the rods can easily be shortened. As I have already mentioned, it is extremely time consuming running nuts up and down such fine threads!

Click on any image for an enlargement.

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8" Fullerscopes on eBay[UK]

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Fullerscopes "8 Telescope Large Vintage Telescope Wooden Tripod Industrial Prop | eBay

 

A garage find in need of some serious TLC.

8" Newtonian on a MkII/MkIII mounting with original tripod.

A finder, slow motions, RA drive motor and setting circles are all present. Hopefully the worms are not rusted solid. A Fullerscopes slip ring is provided to allow tube rotation for comfortable eyepiece angles.

The mirror sounds as if it needs re-coating. One must pray that the seller does not try to "re-polish" it himself!

Should make a nice restoration project.

The dog seems fascinated. A budding observer? Or does it want to bite the leg of the tripod?

The auction closed on £123 after 10 bids.
I can remember an almost identical instrument from decades ago.
With a little TLC this could become a fine instrument again.
Offering a level of sturdiness and ease of use which more modern instruments can only dream of.

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7" f/12 iStar refractor 8: Countercell & dewshield?

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I am presently considering how I might use the raw materials of the nesting components of the 10" steamer to best effect. Adding internal plywood rings would increase the weight and undo the entire purpose of making the counter-cell as a thin and hollow but very stiff shell. Besides my lathe is already at the limit of maximum turning diameter. Fortunately the router with circle cutting jig does a good job of achieving roundness and patience in setting will provide accuracy in diameter. Carbon fiber would be ideal for a counter-cell but I don't want to get involved in the mess or the expense. I have had quite enough experience with building things in GRP to last me a lifetime!

The 10" steamer base pretending to be an APO dewshield.

A search of the village recycling shops provided another, larger, but still lightweight, aluminium steamer. A 10" diameter one this time. It looked absolutely huge as I stuffed it into my cycle shopping bag. To add to the fun the charity shop was having a half price, sales day.  Once the steamer was safely brought home it shrank dramatically when held up against the 8" diameter main tube. Despite its considerable depth the steamer base pot looked rather tragic as a potential dewshield. The sense of scale in a larger, classical refractor demands a dewshield length of at least twice the aperture.

Dewshields are odd things from a purely aesthetic point of view. I have very specific tastes in dewshields which simply cannot be ignored. It must be neither too long nor too short. Of the correct diameter, without protruding cell flanges. Above all dewshields must be larger in diameter than the main tubes or it looks completely wrong.

My fixation is probably the result of my childhood yearning for a 3" Swift refractor. This was prominently displayed in a library book, on basic astronomy, which I often borrowed. As a schoolboy I only had a 1" draw-tube refractor at the time in which the image of the Moon at 30x was a fuzzy mess. Seeing through a pair of ex-govt. binoculars was a revelation! It was years later before I finally had a pair of binoculars to call my own. Decades before I had a half decent pair.

Far too many hobbies meant my pocket money was constantly spread too thin. Nothing has really changed in the ensuing 50-odd years. I still have a wish list twice as long as my arm and at least a hundred times the thickness of my wallet. My constant recycling of available raw materials [like cooking pots and pans] is a chronic symptom of making do with whatever was to hand at lowest cost. I also have my pride and will not tolerate shoddy workmanship or inappropriate appearance. Though I am not one to spend hours preparing a surface for a perfect paint job. Life is too short when function comes well after appearance. 

The image above shows the steamer base opened out to fit the objective cell OD and denuded of handles and drainpipe. Note the closeness of the main tube and cell diameters. It occurs to me that I could reverse the "pot" to make a shallow, mechanical dewshield. This would support the plastic dewshield and provide a really stable base on which to to rest the OTA vertically. The problem is getting a strong fixing onto the main tube. Though I have some new ideas for that too.: A couple of plywood rings can clamp the counter-cell/dewshield over the main tube flange. The rings would have to be split and glued once they are sprung over the flange. I have cut a couple of circles but could make some more with extended ears for a bolt style clamp. I'd rather avoid using a mechanical clamp over the plywood rings for aesthetic reasons. This fixing is absolutely vital from both a stable collimation and security point of view. I can't have the heavy lens falling off the end of the telescope tube! Perhaps I should reconsider a counter-cell which is inserted into the main tube? Or a belt-and-braces design.

I split the two 12mm thick Birch plywood rings I made yesterday and sprang them over the main tube flange. Once i was happy with the fit I glued and clamped them together with every clamp and vice I could muster. Wood glue is suppose to be stronger than the material it joins so it should be up to the task.

Fuzzy image in a dark shed of the clamping operation. One day they will invent a light for photography in dark places. "Flash" might be a good name for it. [sigh]

I deliberately cut the rings at an angle to increase the joint area for extra strength. Once these rings are bolted through the dewshield/counter-cell pot the whole arrangement should be more than strong enough. A few radial screws will ensure that the plywood rings never come loose even if the disintegrate over time. Though there's no reason why they should as they are WBP birch multiply. The donated steamer base weighs almost nothing and the rings are narrow enough not to add much weight of their own. I would have preferred not to use plywood but nothing else suggested itself. Only the router could manage circles of the required diameter. They were at least an inch larger than my lathe can manage.

Of course we had a cloudburst right in the middle of the clamping operation! So everything had to be rushed back into the workshop. I had been working outside for good light and maximum freedom to move around the job. I wanted to ensure I had missed no gaps between the rings and the main tube so that the cut joints were tight. I put a slight chamfer on the foremost ring to ensure it bedded as closely as possible against the main tube flange. A notch was also required for the main tube seam. Now it's just a matter of patience until the glue sets. It's a shame the temperature has dropped 20F in the last few days.

I went out in search of some 4mm screwed rods [studding] and some thin alloy flashing to start making up the baffles. Anything thicker than 4mm quickly gets quite heavy when a minimum of six is required.  The first store only had two rods and the second store was already closed. Denmark has a long history of shops closing early on Saturdays. Somewhat ironically the same shop will be open tomorrow. The important baffle hole to get right is the middle one. Since this is where the pairs of rods join leaving little room for manoeuvre. The other baffles can be moved up and down inside the tube simply by adjusting their fixing nuts. I think I shall have five baffles separated by two sets of three rods. Each set will be rotated relative to the other to avoid having to join them end to end. The middle baffle will become the joining plate for the two sets of rods.

I have been testing the balance point of my still unfinished OTA by hanging a 5kg weight to represent the objective. It will need considerable weight added to the focuser end. I can add a sliding weight and a finder but it will probably still need more ballast if it is not going to look like it has slipped down through the rings. No to mention the lack of ground clearance this causes when pointing at the zenith. My wife suggested I strip our old [small] trailer down to the chassis. So I could easily push the MkIV mounting around on its pier. That would get me some instant ground clearance! It would need some thought as to rapid stabilization and a brake once it was parked.

The suspension had rusted up years ago [as purchased!] which made it an automatic failure on the MOT. So, at least, suspension sag isn't a worry. Stripped of the bodywork it would be much lighter and have better access to the telescope at high pointing altitudes. I haven't looked at the tyres in years since it was never actually used on the road.

The supposed "Vixen" tube rings I have just received in the post have a crack in the casting right across one of the hinge "ears." The quality of the casting, machining grinding and fettling really is complete crap. Nothing like the quality of the rings which came with my [secondhand] Vixen 90M refractor. What makes matters worse is that all of the "Skywatcher" rings I have collected, for assorted OTAs and guide scopes, are also far better made and finished!

These rings will have to go back. It's lucky I didn't open out the fixing bolt hole to match the needs of the sturdy MkIV mounting saddle. It's a shame because the next ring size up is even larger than these. Nobody seems to do a budget 202mm ring. Except for Orion UK which offers "rolled" alloy rings in many sizes including a 202mm which I need. Perhaps I should make some tube rings out of birch plywood using the router? The problem then is fitting a hinge and a clamping screw. I shall have to do some online homework to see how clever people have coped with the clamping problem.

I now have 6 x 1m x M4 screwed rods to build the baffle assembly. The rods alone weigh 1lb! Fortunately the weight is evenly spread along the entire OTA.

Click on any image for an enlargement.

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7" f/12 iStar refractor 7: Rotating focuser.

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Latest progress: I have fitted the large Vixen focuser to the back plate. More by serendipity than deliberate intent the three fixing screws provided a perfect chance to make the focuser fully rotatable. I had to turn the screw heads down repeatedly in the lathe until they allowed complete freedom of movement against the inside of the back plate. Just to help matters along I added some thin plastic tubing to the screw threads but could improve these further to kill the slightest bit of "slop".

The back plate is not a finely turned surface so some leeway must be allowed for very slight irregularities. I could fit a liner between the screws and the focuser back plate. Above all, I want to avoid a circular scar in the matt black paint on the inside of the back plate due to turning the focuser repeatedly over time. The particles of scuffed paint might find themselves where they are not wanted as the telescope is constantly moved around.

This image shows the three, overlong, retaining screws in place. At first I thought I was going to have a serious problem getting a fixing on the narrow Vixen flange. When I experimentally fitted the three screws I could hardly believe my luck. It would be so easy to provide a fully rotatable focuser for very little effort. Note the scuff marks from earlier attempts with larger screw head sizes.

It was important to be able to tighten these screws fully home in their threads to ensure they were safely locked in place. I tried using pliers but there was too little room to grip the small screw heads so close to the back plate. In the end I bored a small hole in the rim of the back plate to be able to insert a long, thin screwdriver. The focuser back plate will need to be sprayed flat black inside to kill all reflections. A thin sheet of black plastic proved to be too thick and prevented the focuser from turning. The screw heads cannot be made much smaller without loss of driver function.

The objective cell fitting is another problem altogether. I had originally planned to have a flanged tube inserted into the main tube, probably using the other saucepan for raw materials. However, the difference in diameter between the 200mm main tube bore and the 195mm OD of the cell body made this impossible. Now I have a dimensioned drawing of the cell I can see that I need a much larger flange to take the cell adjustment screws. The flange must be inward facing if a larger tube is used.

Even without the focuser fitted the bare OTA now stands over 7' tall while balancing on its nose!

I have no desire to cripple my OTA with  massive, solid aluminium counter-cell. A counter-cell is really no more than a pipe-size adapter. It need not be any stronger than that required to support the weight of the glass and its cell without flexure. If it should flex then collimation will change with the OTA's attitude. If it is heavy it will force the objective towards the mounting to achieve balance in the tube. A common enough sight with refractors. APOs are particularly vulnerable with heavy triplet objectives.

The increased weight all adds up to a heavier OTA to carry about. Worse still is the increased moment arm of adding unnecessarily  heavy components on the extreme end of the long, main tube. The greater the moment arm the worse the handling and damping times on a typically undersized mounting. We are looking for a revolution in refractor weight reduction here! Weight is the one luxury which most amateur astronomers cannot afford. Yet reviews often mention the "solid construction inspiring confidence" in the quality of the instrument. Short-sightedness or just typical hype and bullshit?

I am not in the market for an AP1200 or even larger mounting as are many amateurs struggling with a heavy refractor. Adding solid "CNC'd" components to already heavy refractor tubes is much like handing out free takeaways at Weight Watchers. Can you imagine rewarding members for gaining even more weight? The whole idea is simply ridiculous in a famine of affordable telescope mountings. See me! See my pot-bellied refractor, Jimmy! 

Needing a larger counter-cell actually aids my cause when fitting a dewshield. Ideally I need another saucepan which fits comfortably over the main tube and provides a larger diameter base for the dewshield and objective cell to sit on. The base of the pan will provide the necessary flange for the "push-pull" adjusting screws of the objective cell. I will need packing between the main tube and the inside of the empty counter-cell shell. Since the main tube is flanged I shall have to use a split shell turned in the lathe for accuracy of fit. Probably made from rings of Birch plywood. Though I should also examine alternatives which would allow an easily retractable dewshield.

I would still like to arrange a solid front edge to the OTA. To allow it to be rested on its nose without risking the precious glass. My planned, self-rolling, black plastic dewshield will not take the weight of the OTA and will be highly vulnerable to damage. The plastic makes a stiff and ultra-lightweight [light and] dew shield. It is deliberately not made a structural part of the OTA. The intention was to slide the dewshield  back over the main tube, when in storage, to help reduce the great length of the OTA.

Click on any image for an enlargement.

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