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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