Improvements in Telescopes.
Year: 1895

page_text: Date of Application, 18th Apr., 1895-Accepted, 18th May, 1895
COMPLETE SPECIFICATION.
Improvements in Telescopes.
I, ALFRED CONRAD BIESE of 32 Maassenstrasse, Berlin, in the German
Empire, Engineer, do hereby declare the nature of this invention, and in what
manner the same is to be performed, to be particularly described and ascertained
in and by the following statement :-
This invention relates to telescopes and its object is to provide means for
varying the magnifying power of such instruments, an object which is achieved by
interposing a movable convex lens between the object glass and the eye glass.
The accompanying drawings illustrate in what manner this invention may be
carried into effect.
Figure illustrates in longitudinal section a terrestrial telescope with the
interposed double convex lens.
Figure 2 shews a diagram of the object glass and the interposed double
convex lens.
The position of the double convex lens has the effect of varying the apparent
focal length of the object lens, that is, the position of the image formed by the
objective is varied as the interposed lens is moved. In Figure 2 the objective O is
of the ordinary kind and forms an inverted image at A B. By placing the lens S
between the objective O and the point B the image is removed to D and becomes
of the size CD. SF is the focal length of the lens S. The focus of the
combined lenses is thus situated at D the focus of the original objective O being
apparently shortened. The focus of the lens O and the size of the produced image
may thus be varied. If means be provided which allow the eye glass to be always
maintained at the same distance from the image C D then a telescope with variable
magnifying power is obtained.
Figure 1 illustrates one method of carrying this invention into effect. The
tube a carries the object lens O and is furnished with a sliding or movable tube b
provided with the lens S. Within the tube b slides the tube c fitted with the lens
or lenses forming the eye glass. The farther the lens S is from the objective O
the greater will be the size of the image the maximum being obtained when the
lens is placed at the point B. In this case the lens S does not act optically as the
image is formed within its substance. If the lens S be gradually brought
nearer to the objective O the image will gradually diminish until it reaches its
minimum when they are close together. As the lens moves towards the objective
and the image consequently recedes from the eye glass this latter must be
correspondingly moved.
In a Galilean telescope the greatest magnification of the image would be obtained
when the double convex lens was brought against the eye glass and the smallest
when it was brought against the objective.
In terrestrial telescopes the extra double convex lens may if desired be arranged
between the different lenses forming the eye piece.
Many methods of varying the distance between the double convex lens and the
objective and between the double convex lens and the eye glass may be adopted.
For instance, the objective may be moved away from the lens S or the lens S may
be moved away from the objective by moving the sliding tubes by hand, whilst the
motion of the eye glass may be effected by means of a worm or screw, as is now
usual in double Galilean telescopes or opera glasses.
Mechanism may also be employed which effects the movement of both tubes at

page_text: the same time. One tube may be moved at a uniform speed whilst the other may
be moved by a screw or worm the thread of which is cut so as to give a movement
corresponding with the movement of the image, so that the image is continuously in
view but is enlarged or diminished in size.
An advantage attendant upon the use of this invention is that it is possible
without removing the eye glass of a telescope to reduce its magnifying power and
thus obtain greater clearness and a larger field of vision.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. The combination and arrangement with the eye glass and the object glass of
a telescope of a double convex lens substantially as and for the purpose hereinbefore
described and as illustrated by the accompanying drawings.
2. A telescope constructed and arranged substantially as and for the purpose
herein before described and as illustrated by the accompanying drawings.
Dated this 17th day of April A.D. 1895.
W. E. HEYS & SON,
Agents for the Applicant.