GB2308676A - Terrestrial telescope having four mirrors - Google Patents

Description

TERRE5TRI AL TELESCOPE This invention relates to a terrestrial telescope.

Terrestrial telescopes are telescopes used for viewing objects on the ground the right way up. They can also be used for astronomy.

In order to view objects upright modern telescopes use a refractor (lens) system to magnify and focus the image. This system has been used for many years without change, except in the most expensive types of terrestrial telescopes where prisms are included to invert the image and shorten the overall lengh of the telescope.

On the other hand most telescopes that are used for astronomy use a reflector (mirror) system to magnify and focus the image, unfortunately the image is always upside down, but this is accepted because reflectors produce a brighter clearer image than refractors.

According to the present invention there is provided a terrestrial telescope which uses a reflector system of mirrors to produce an image the right way up so it can be used for terrestrial viewing as well as for astronomy.

According to the present invention the upright image is produced by utilising 4 mirrors and an eyepiece (eye lens) mounted in and around a suitable length of open-ended tube, capable of observing an image, inverting thet image and presenting that image to the eye in an upright form and without 'mirror image' i.e. lettering appearing backwards.

There is also included in this present invention a 'sighting' mirror positioned adjacent to and in line with the eyepiece and angled at 45' > to the observer's left eye to enable the observer to roughly align the telescope with the object to be viewed.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows in perspective a simplified view of the arrangement and relative positions of the four mirrors 5,6,7 a 8 and the eye lens 9 along the focal path 19 which together produce the upright image.

Figure la shows in perspective a simplified view of a common Newtonian reflector telescope in use today. Its inclusion is for comparison purposes and to help understand the working of this present invention.

Figure 2 shows e side view of housing 20 that contains mirrors 6,7 & 8 and rack & pinion focusser 12 within a working model of the present invention.

This complete unit is housed on a seperate sleeve 11 which is held in position on tube 10 by two screws 18. The whole unit can be removed from tube 10, this then allows access to mirror 6 through aperture 22 for cleaning purposes. Mirror 6 is positioned in the centre of tube 10 and angled at 45 in relation to the direction of the focal path reflected from mirror 5, this 450 angle faces mirror 7. Mirror 5 is not shown in this drawing because the side elevation makes it difficult to include, however the direction of mirror 5 is indicated by arrows in figures 3 & 4. The exact distance of mirror 5 to mirror 6 is not a fixed distance but is determined by the focal length of mirror 5, which can vary in manufacture.

The focal path 19 is indicated between mirrors 6 a 7 also between mirrors 7 & 8 and between mirror 8 & eyepiece 9 Figure 3 shows a birds-eye view of housing 20 containing rack & pinion focusser 12, diagonal mirror 6, diagonal support body 25, support arm 24, sighting mirror 15 and adjusting screw 16. The direction of mirror 5 is indicated by the dotted arrow. Sighting mirror 15 is elliptical in shape and is angled at 450, it is adjustable so that an observer can line up the telescope with the object to be viewed with the left eye while the eyepiece is focussed for the right eye.

Figure 4 shows a front view of housing 20, rack & pinion focusser 12 and sleeve 11 together with 'sighting' mirror 15.

Figure 5 shows sections of tube 10, main mirror 5, mirror support cover 28, removable end cover cap 27, rubber cusion 29, tripod securing nut & platform 26.

A list of components is included on page 6.

Referring to the drawing Fig 1 the image viewed enters the tube on the right indicated by the arrow, travels the full length of tube 10 and strikes mirror 5. Mirror 5 being concave reflects the image 'upside down' and focusses the image back towards mirror 6. Mirror 6 being angled at 450 in relation to the direction of the optical path, reflects the image at an angle of 900 towards mirror 7. Mirror 7 which is also set at 45 in relation to the direction of the optical path, reflects the image at an angle of 90'' towards mirror 8 where the image is inverted by mirror 8.

Mirror 8 being also set at 450 in relation to the direction of the optical path, reflects the inverted image at an angle of 900 towards the eye lens 9. The eye lens 9 focusses the image into the eye where the image is received by the eye the right way up. It should be noted that the complete inversion of the image takes place due to the position and angles of mirrors 7 and 8 in relation to the direction of the optical path 19 and the position of the eyepiece.

Referring to the drawing Fig la, depicting a common Newtonian telescope in use today, the image enters the tube on the right as in Fig 1 striking mirror 5 which reflects the image back 'upside down' to the diagonal mirror 6, this mirror being angled at 45'' towards the observer, reflects the image to the eye lens and then to the eye where the image is received by the eye in an upside down condition.

Referring to the drawing Fig 2, this shows the focal path 19 and indicates the way the image is inverted between mirrors 7 & 8. To ensure a perfect upright image, the image reflected by mirrors 6, 7 & 8 must be reflected at 900 sngles and the eye-piece must be exactly in line with the reflected image from mirror 8.

The rack a pinion focusser 12 being mounted across the top of tube 10 has a long adjustment, this enables a wide focussing range of the present invention to be made, from infinity right down to a few meters.

The two mirror covers 14 containing mirrors 7 & 8 are held in position by screws 23, this allows removal of mirrors 7 & 8 for cleaning purposes.

The eyepiece 9 is held in position by eyepiece holder 13 and is secured by eyepiece retaining screw 21.

The sizes of mirrors 6, 7 b 8 are determined mathematically according to the size and focal length of mirror 5. Mirrors 7 & 8 should be big enough to reflect the full focal image, while mirror 6 should be as small as possible so as not to block off too much light entering tube 10, but at the same time be large enough to reflect the full focal image.

Because the focal path 19 is folded around tube 10 this has the effect of shortening the focal length within the telescope, so o shorter telescope body can be utilised.

A terrestrial telescope as described in this present invention is not restricted to one size or one magnification but can be increased in size and magnification by using a larger mirror 5 with a longer focal length and a stronger eyepiece 9. The prototype used in this present invention uses a 66mum diameter mirror 5 with a focal length of 710mm, together with an eyepiece 9 giving a magnification of 35X and a focal aperture of F10 with an overall telescope length of 660mm.

There is one aspect of this present invention that has not yet been mentioned and that is the changes of 'mirror image' that take place along the focal path. Referring to the drawing Fig 1, the image striking mirror 5 is reflected upside down and is also a 'mirror image' i.e. any lettering would appear reversed as well as upside down. This 'mirror image' is corrected when reflected by mirror 6 but the image is still upside down.

When the image is reflected from mirror 7 it is once again a 'mirror image' and the image is still upside down, but when the image is reflected from mirror 8 it is free from 'mirror image' as well as being the right way up.

The terrestrial telescope described in this present invention can be made into a sealed unit by the inclusion of a circular flat piece of clear glass fitted inside the open end of tube 10. This would keep out dust and moisture etc. but it would have to be optically perfectly flat to prevent any distortion of the image, it may however reduce brightness slightly.

All mirrors mentioned in this present invention are surface coated (aluminised) and quartz over coated for protection and longer life, except sighting mirror 15 which is an ordinary back coated mirror.

All drawings shown in figures 2 to 5 are all drawn to size.

LIST OF COMPONENTS 5 Main or primary concave mirror (Newtonian) 6 'Diagonal' flat elliptical mirror.

7 Flat oblong mirror.

8 Flat oblong mirror.

9 Eye lens (eyepiece).

10 Tube (telescope body).

11 Sleeve.

12 Rack & pinion focusser.

13 Eyepiece holder.

14 Mirror cover.

15 Sighting mirror.

16 Sighting mirror adjusting screw.

17 Rack & pinion focussing wheels.

18 Sleeve retaining screws.

19 Focal path.

20 Housing.

21 Eyepiece retaining screw.

22 Aperture.

23 Mirror cover retaining screw.

24 Diagonal mirror support arm.

25 Diagonal mirror support body.

26 Tripod securing nut & platform.

27 Removable end cover cap.

28 Main Mirror support holder/cover.

29 Rubber cusion.

30 Retaining screws for 28.

Claims (3)

1. I A terrestrial telescope which uses a reflector system of mirrors to produce an image the right way up so it can be used for terrestrial viewing as well as for astronomy. Comprising of 4 mirrors and an eye lens or eyepiece. mounted in and around a suitable length of open ended tubing, capable of observing an object, inverting the image, magnifying and presenting the image to the eye in an upright form and without 'mirror image' i.e. lettering appearing backwards.
2. 2 A terrestrial telescope as claimed in Claim l wherein 2 extra mirrors are included in the optical path of a reflector type telescope to invert an image so that the object is viewed upright and without mirror image.
3. 3 A terrestrial telescope as claimed in Claim 1 or Claim 2 wherein a sighting mirror is provided to allow an observer to align the telescope to an object being observed with one eye while simultaneously looking through the eyepiece and observing the magnified image with the other eye.