28.10.12

Fullerscopes finder telescopes:

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Thanks to Clive, my contact in the UK, I have another selection of photographs of Fullerscopes equipment to share with you:

Fullerscopes provided many different sizes of astronomical instrument. Each would have to be pointed quickly and accurately at objects to be viewed in the night sky. Otherwise a great deal of valuable observing time could be completely wasted simply searching for the almost invisible object. Most amateurs are acutely aware of the frustration caused by this problem.

Pointing a telescope by squinting along the main telescope tube, like a cannon, will only work for very low powers and big, bright objects like the Moon. As soon as magnification increases the field of view often shrinks to only a tiny fraction of the size of the full Moon. Sometimes to only an area the size of a single, modest crater. Sighting along the tube will obviously not work at high magnifications.

The answer to this quite serious observing problem is to attach a small "finder" telescope to the tube of the main instrument. The finder need not have high magnification itself provided it is fitted with some means of sighting accurately within its own field of view. The usual means of accurate pointing is the use of crosshairs. Not unlike a telescopic sight on a rifle. The small telescope magnifies the sky by a modest amount while simultaneously providing the pointing accuracy of cross hairs. It also provides a brighter image than the human eye can manage on its own.

The size of the primary instrument dictates the size of the ideal finder telescope to some extent. A larger instrument is obviously capable of much higher powers and able to see much dimmer objects. A tiny finder will be lost trying to see the dim object. Let alone achieve the accuracy of pointing necessary at very high magnifications on the main instrument.  


Means must also be found for ensuring both the main telescope and the finder point at exactly the same point on the sky. This is easily taken care of with oversized rings and screws spaced 120 degree apart. The main instrument is pointed as something easy to find. Something like the moon is helpful. The view through both instruments is compared at lower powers while the finder is adjusted in its rings toe ensure both point at a particular object. Once this is achieved on a larger object then finer adjustment can take place on a planet or bright star.


The smallest finder in the Fullerscopes range is the 6x30. Six magnifications with a 30mm objective lens. Crosshairs are provided at the eyepiece focus. While great optical accuracy is unnecessary any distortion or false colour will be very obvious on bright objects like the Moon and planets. Thus a minimum standard of quality is set if the entire instrument is not to seem cheapened. After all, binoculars in this size are readily available at relatively low cost.

In fact many amateurs have made their own finders using plumbing tubing and binocular or opera glass objectives and eyepieces.

This view rather emphasises the relatively small size of a 6 x 30 finder. On a larger instrument it will seem even less significant. Magnification is low and light gathering power limited. It may be useful for coarse pointing of the main telescope but quickly runs out of usefulness.
To reach dimmer objects and provide greater pointing accuracy higher finder magnifications a larger finder is offered. The 10x 40 is a useful step up in power on larger instruments. The accuracy of the crosshairs pointing ability is improved. A 40mm objective brings in dimmer objects when searching for the elusive fuzzy nebulas.
 The adjustable screws for centring the finder with the main instrument are well seen here.

The quality is high and the design well thought out. With large thumb wheels and locking rings. Ideal for the many colder nights when the observer is wearing gloves. The need for tools is very undesirable for centring a finder.
It should be possible to centre the smaller telescope with the field of view of the larger instrument without serious effort.


The perennial problem with finders is achieving good eye relief. A finder which requires too close a proximity of the eye can often become completely impossible to see through at some main telescope tube orientations.

A longer focus finder thus has some advantages. A lower power eyepiece with longer eye relief can be used for the same power as a shorter focus finder with higher power eyepiece.
Having a number of finders is often an advantage with a larger telescope. The weight and complexity of multiple finders loses significance with larger instruments. They aren't usually portable anyway.

So the observer merely chooses the most appropriate finder depending on where the telescope is pointing. It should not be forgotten that many observers will have a favoured observing eye. Trying to use a telescope or finder with the "wrong" eye can mean a finder has a little value.


Here the finder has been increased to a much larger aperture and power. A 20x60 can be used as  guide telescope. As well as seeking smaller, dimmer object for the main instrument to  examine. This is quite a sophisticated finder with flared tubing and a 'proper' star diagonal. Promising high quality images and freedom of rotation of the eyepiece to match the observer's needs.
This instrument belongs to the family of "elbow" telescopes. By means of a star diagonal (or prism in some cases)  the finder can be used in the same plane as the eyepiece on a larger Newtonian reflecting telescope. This avoids unwanted observer contortions. Or having to leave the main eyepiece just to use the finder. An elbow finder can save a lot of frustration when searching for a difficult object.

Finder field of view orientation can be a problem if it does not match the main instrument. A diagonal will reverse the view. Rotating the star diagonal will rotate its field of view. Imagine trying to match the view seen through both instruments to home in on a difficult object at the limit of vision.
Some finders are "scaled down" to non-standard eyepieces. Here a full sized star diagonal and eyepiece is used. Allowing some freedom to change powers. (provided the new eyepiece has crosshairs of course)

Here the finder rings are of generous diameter to allow the finder to be skewed relative to the main telescope. When taking photographs of dim objects (like nebula and star clusters) there may not be a suitable "guide" star. The finder is then offset on a suitable star which can be monitored for any wandering and the main instrument drives or slow motions corrected.

Here the star diagonal and standard eyepiece are clearly seen. It is not always necessary to use a very high quality eyepiece in a finder. Adequate eye relief is a far more important consideration. Some eyepiece designs offer inherently poor eye relief and small fields of view. These must be avoided so the observer can easily get behind the finder eyepiece.





Now we have moved well beyond the normal scale of telescopic finders. This is the 4" (100mm) Fullerscopes photographic guide telescope. It provides greater aperture and a longer focal length. The latter provides more "optical leverage" when trying to hold the main instrument accurately centred on the object being photographed.

The guide telescope is a 4" reflector in its own right. It has a proper rack and pinion focuser, mirror cell and diagonal spider. Such an instrument was, and remains, a popular first telescope and was sold as such by Fullerscopes with its own MkIII mounting.

The advantage of such an instrument is that it provides a brighter image. The star being followed can even be thrown slightly out of focus and held on the crosshairs more easily than in a smaller refractor finder.

Here the adjustable mirror cell is seen with spaced screws to allow accurate optical collimation.


The centring rings allow the guide telescope to be adjusted to point at a nearby star when the instrument is photographing another object.

This photographic guide telescope is about to be restored by its owner to its former glory. It sits atop a 10" Fullerscopes Photographic Newtonian.



Click on any image for an enlargement.
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26.10.12

Part 3: 12" OTA restoration.

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This is the third post in this series illustrating the restoration of a 12" Newtonian-Cassegrain, Fullerscopes reflector on a MkIV mounting.

 The adjustable Newt-Cass cell mounted on the backplate with the perforated primary in place.
The long tube is to block stray light from diluting the field of view. The observer is looking straight up at the open end of the tube. So the optical path must be reduced (by the tube) to only the area obscured by the small secondary mirror. Thus the light from the open sky is blocked.

Matt black paint is always used inside the OTA (optical tube assembly) to kill all stray light reflections.

This instrument has F5 or F30 optics depending which optical system is used. The convex Cassegrain secondary mirror amplifies the primary image to produce a large primary image scale for planetary or lunar photography. When the convex mirror is swapped for a conventional diagonal mirror the instrument performs like any other F:5 Newtonian telescope.

The main tube has been resprayed and the ring components cleaned, primed and repainted with Hammerite. It takes skill and lots of patience to achieve a fine finish like this. Making haste will never achieve such results.




A view down the main tube towards the primary mirror. Though the backplate assembly and primary mirror are absent in this view. Note the overall use of matt black paint inside the tube to kill stray light.

The secondary mirror cell will be mounted at the centre the four vane spider. The narrow blades of which are tensioned to avoid sag. Which would ruin the focussed image.

Great accuracy is required in optical alignment. Leading to potential difficulties with a convertible Newtonian-Cassegrain.
Simply changing the secondary mirror will require tiny and tedious adjustments to optical alignment.



The OTA in all its glory after restoration. The Hammerite 'Charcoal' paint offers an updated alternative over the original matt black wrinkle paint.

Note the two access doors. The larger one is to allow the primary cover to be removed before use.

The other door is to allow the secondary mirrors to be swapped between the two optical systems.

Another view of the superbly restored main tube. The mounting rings and guide telescope rings have been treated to the Hammerite finish and look fabulous compared with the tired, original paint.

Such restorations are always a difficult choice between total authenticity to the factory gate finish. Or an updated version designed to inspire potential new converts to amateur astronomy.


Stages in the restoration of the classical 3" F/15 refractor, photographic guide telescope. Fullerscopes offered both refractors and 4" reflectors as photographic guide telescopes.          
The gloss white and polished brass dewshield look well together after restoration. The great length of this small instrument can look surprising to our modern eyes. Where refractors have been reduced to a fraction of their former length. Not always with the best results. Chromatic aberration is a unavoidable with increasing aperture and reduced focal length.

An advantage of a guide telescope is that it may be used in its own right. Either for solar observation. (with a suitable solar filter and the main instrument covered) Or when a second observer is present and both wish to see the same object visually. At the time this entire instrument was built a 3" refractor was often the only instrument available to many amateurs. Many amateurs forget that a great deal of real science was done with such small instruments.

Components being painted with primer prior to a Hammerite finish. Hammerite requires its own primer to achieve good adhesion to non-ferrous materials like aluminium, brass and bronze. Warmth is useful when painting. Particularly with Hammerite. Unless warm, well-ventilated conditions can be provided, restoration is best carried out in summer. Or delayed until reasonable warmth can be provided.

The sheer bulk of the mounting rings shows the huge scale of this large instrument. The main tube is probably 15" in diameter. Telescope tubing is usually made made larger than the aperture of the instrument to avoid the light path being affected by heat currents clinging to the tube walls. A larger tube also allows ring baffles or matt black paint to avoid low angle, reflected stray light from interfering with the image. Many supposedly matt surfaces reflect very easily when the light is just glancing off the surface.

Hopefully further images showing the MkIV mounting after restoration will become available.

I am most grateful to my contact in the UK and the skilled restorer in Australia for sharing these unique and fascinating images of the restoration of such an interesting instrument.

Click on any image for an enlargement.
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Part 2: 12" Fullerscopes Newt-Cass restoration

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Back to this restoration project of a 12" Fullerscopes Newtonian-Cassegrain in Australia. The previous image shows the instrument as found on its MkIV mounting in a white GRP dome.

 The cast rear backplate houses the primary mirror cell and the Cassegrain focussing mount.

The original condition does not inspire great confidence. The paint is oxidised and the metal parts corroded.

No doubt the focusser needs careful dismantling and restoration too. The focuser has its own alignment screws. Which will need great care.

Rusty screws must be treated with patience. By applying easing oil well before any attempt is made to remove them.
 There is a lot of messy work removing old finishes even when great care is required. You can't just attack the components without the risk of damaging the original finish or fine details.

A mask is essential to avoid inhaling possibly toxic finishes from the past.
 Here is the finished and painted backplate.

Even the Fullerscopes logo has been picked out in gold. A nice touch which adds a hint of sophistication.

I believe the paint is Hammerite "Metallic Charcoal."


The Fullerscopes MkIV mounting before restoration. The paint is dull and weathered. 

The details are all badly in need of smartening up. 

Supporting the parts on a sturdy working surface with protective cover avoids unnecessary damage to finishes and parts.

Restoration requires thought, patience and care. Simply pulling a rusty shaft through a bearing can do a lot of damage.
Here the components of the MkIV have been disassembled.

The main castings now have their shafts exposed. We see the slow motion worm wheels (actually rings in this case) and their drive worms in their cast housings.

The large Declination circle is the perforated casting in the foreground.

On the right are various bolts, screws and the slow motion locking wheels and threaded rods. Two white circles are thin sheet PTFE. (Teflon)
This helps to reduce friction between rubbing surfaces.

A collection of small parts undergoing examination and restoration. Note how everything is kept tidy in shallow trays to avoid loss of vital, original parts.

Even obtaining bolts and screws with original threads can be difficult in this time of almost universal metric threads. Some of the original fasteners have coarse threads to maintain strength and holding power in the soft aluminium alloy castings. Metric threads of similar dimensions have very poor holding power in such soft castings.

Some of the weakest parts of the MkIV design are the Polar Axis pivot bolts. These pass through 'ears' on the base casting and screw into the Polar Axis casting itself. A heavy instrument or any out of balance forces can easily strip these threads. This is where an inexpensive turn-buckle is so useful. It removes the need for the pivot screws to resist unbalanced loads around the pivot screws.

This is part two of the 12" telescope restoration. The next post will show the main tube, guide telescope and their restoration.

Here is a link to Xavier's own MkIV restoration:

http://support.internetmarketingsolutions.be/gallery3/index.php/Fullerscopes-MK-IV/fullerscopes_mkiv01

Click on any image for an enlargement.
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Part 1: A 12" Fullerscopes Newtonian-Cassegrain reflector.

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My contact in the UK has been in correspondence with a gentleman in Australia who has been restoring a large Fullerscopes reflector. The pride of the Fullerscopes catalogue: A 12" Newtonian-Cassegrain on a driven MkIV mounting. The combination provided a convertible instrument. One which could provide high powers for planetary work via the Cassegrain optics. Or, with a change from a small convex secondary mirror to a flat diagonal: Provide the wider views normally associated with the Newtonian.

It must be remembered that the Fullerscopes era was prior to such large instruments becoming almost commonplace. A 12" was considered a large instrument when this one was manufactured.

The instrument is housed in a very attractive, rotating fibreglass dome. The protective enclosure may simply be a secure resting place prior to installation. Its present situation would seem to limit the view of the sky to high altitudes.

The view inside the dome proves how large the protective enclosure must be in practice. The following images are pror to restoration.

The sheer scale of the instrument is obvious from the way it makes the already-large, MkIV mounting seem small. Mounted on top of the OTA is a 3" classical refractor. The adjustable guide rings allow the smaller instrument to be used as a guide telescope for photography. It can be moved, relative to the main telescope, to point on any nearby star or object. The main instrument field of view would not be available during photography due to the film cameras used at this time. A very long focus guide telescope would allow high magnifications with low power eyepieces. The photographer could use the star in the field of view to make small corrections to the drives. Allowing the main instrument and its camera to remain fixed precisely on the object being photographed.

The view of the instrument from the other side. The smaller, finder (telescope) is of ample proportions in itself. A small finder on such a large instrument is pointless. It would mean that objects in the field of view of the finder would be so much dimmer than the main instrument. It would thus be difficult to home in on dimmer objects which are easily within the grasp of the 12". 


A closer view of the MkIV showing the AWR drive motors. These are a later addition. They provide not only greater power over the original synchronous motors but tighter control of the instrument's movements. Slewing may even be possible. A feature which eludes the slow change of speed of the original motors. The Fullerscopes paddle and VFO control unit only allowed very modest changes to the sidereal drive speed.



Another view of the telescope on its mounting. Note the poor condition of the original black paintwork. It has faded to a dull grey in the time it has been housed in the observatory. Perhaps UV light can penetrate the dome despite the white paint applied over the translucent GRP dome.  

The white paint seems to have held up better than the black over the decades. The original black paint would presumably have been Fullerscopes hallmark, black wrinkle paint. Its texture added a hint of luxury to their instruments. Though Fullerscopes did not use it exclusively. Charles Frank used black wrinkle paint as well and may well have inspired Fuller to use it in turn.

The large and heavy instrument is counterbalanced by a number of weights. Showing exactly how heavy the instrument really is. Having the finder and guide telescope beyond the main tube only adds to the counterweights needed to balance the instrument.

The telescope's main tube is fitted with a so-called "slip ring". This would allow the entire instrument to be rotated in the massive, felt-lined mounting rings. The slip ring merely stopped the tube from sliding straight through the mounting rings.

I am most grateful to the gentleman in Australia for these fine images. Also to my contact in the UK for taking the time and trouble to forward the images and technical details. My thanks go to both.

This concludes the images and description of the instrument "as found" in its dome. In the interests of keeping my blog posts user friendly I shall end here and begin another post on the restoration. A large number of images can take a while to download on a slower internet connection. To avoid such users losing patience I shall break this project into several posts. The problem with doing so is that later posts appear first. Showing the finished restoration before you will see the posts with the instrument in its original state. 

Click on any image for an enlargement.
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15.10.12

Some Fullerscopes instruments

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A British amateur astronomer has kindly been in touch to offer images and details of some Fullerscopes equipment. Some he owns, or once owned and Fullerscopes instruments belonging to other amateurs.

First is a very rare image of an even rarer 6" Fullerscopes refractor on a MkIV mounting. Very few of these instruments can have been made and sold. It is said that Wildey made the objectives. This imposing instrument belonged to another British amateur who tragically died before his time.


The classic lines of a long focus refractor is the usual image conjured up when astronomical telescope is mentioned. Such large instruments were very expensive relative to similar sized reflectors at that time. Only recent Chinese mass production has finally reduced the price of such large refractors. This instrument has a well equipped MkIV and a "proper" rack and pinion, refractor style, focussing mount. Albeit of 1.25" size it has an offset, knurled and turned brass focussing wheel. These focusers were traditional in fine instruments of the previous century. Known as the era of "brass and glass." Fullerscopes actually offered all brass refractors. At a price. Who knows how many were made? One 6" all brass refractor was illustrated in the Fullerscopes catalogue for many years.

Now some images of a 10" Fullerscopes reflector and its MkIV mounting: From top to bottom:

Here we see many typical features of a Fullerscopes reflector. A white painted PVC tube is a sign of a de-luxe model. An unpainted model was available at lower cost. Export models were of the highest standard and had polished brass crews and finer optics.

An elasticated vinyl cover for the top of the tube keeps dust, dew and spiders out.

Quite a large finder/guide telescope is fitted in adjustable, centring rings.

A large rack and pinion focuser with slow motion to one control knob is fitted. Modern focusers tend to be much shallower than this example. Allowing a slightly smaller secondary mirror to be fitted. A smaller mirror blocks less light and affects the image quality slightly less.

A so-called, "slip ring" is fitted. This was tightened firmly around the tube to stop it sliding through the twin supporting rings. Thus the tube could be easily rotated if the holding rings fasteners were left slightly loose. There would be no danger of the OTA (Optical Tube Assembly) falling out of the holding rings. Nor would the very slight slackness in support affect alignment.

Top and bottom cast rings keep the tube round and stiff.

An access door is provided at the bottom of the tube. This is for removing the primary mirror, protective cover.


Here is a close-up of the original Fullerscopes cap, finder and focusing mount.

The adjustable screws, with locking rings for centring the finder are clearly seen. I believe this may be a 60mm finder. In keeping with the needs of a 10" reflector and its greater light gathering power.

The focusing mount shows the slow motion mechanism behind the upper control knob. This looks like the Fullerscopes 2" focusing mount. Though focusers of this size are commonplace today they were considered a luxury when this instrument was built.

And now onto the MkIV mounting:

The short, sturdy pier on Heavy Duty cast iron feet provided plenty of stability for this larger instrument.

This MkIV has the "Pot Base" adaptor for fitting the mounting firmly onto a heavy 6" pipe. Screws spaced 120 degrees apart would hold the mounting firm on its pedestal. While still allowing the two to be separated at will. This made for a lighter load if the instrument had to be packed away after an observing session.

The 365 tooth bronze worm wheels are present with synchronous motors in protective brass cans to drive the slow motion worms.

The declination shaft looks like stainless steel. It has the large Fullerscopes engraved circles in place. With two collars to keep the counterweights from sliding off. While allowing removal, if necessary, to reduce the weight of the various components for transport.



Another view of the MkIV showing the original wrinkle paint. The large ring is lined with green felt to protect the tube and allow easier rotation. Rotating the tube made the eyepiece more accessible on a German equatorial mount like this.

Note how the polar axis is pivoted between two screws. Smaller altitude locking screws work in arcs cut in the ears of the pot base.

The protective, brass, motor cans are well seen in this image.


Another view of this smart MkIV showing details of the 2' long cradle for carrying the instrument via the large holding rings.

The bronze worm wheels and the long, threaded drive locking screw (with plastic knob) are better seen here.

The drive lock pushed a nylon plug against the inner surface of the worm wheel ring. This acted as a clutch. Allowing the drive from the worm wheel to drive its respective axis. In other words: The worm wheel became solid with the casting on which it normally rotates freely.

A drive lock and knob is provided on both axes. Loosening allowed rapid movements of the instrument without dragging the worm wheel teeth across their respective  worms. Power slewing is a relatively modern phenomenon.


Click on any image for an enlargement.

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