A New or Improved Apparatus for Ascertaining the Distance of any Object for Photographic Purposes.
Year: 1890

page_text: D.te of Application, 24th Apr., 1890
Complete Specification Left, 24th Jan., 1891-Accepted, 25th Feb., 1891
PROVISIONAL SPECIFICATION.
A New or Improved Apparatus for Ascertaining the Distance of any
Object for Photographic Purposes.
I, HENRY MITCHELL HASTINGS, of 54, Edith Road, West Kensington, Fulham,
London, W., Analytical Chemist, do hereby declare the nature of this invention to
be as follows:-
The special purpose of this apparatus is to ascertain correctly the exact distance
of the object so as to be able to adjust the lenses of cameras where the image cannot
be viewed on the ground glass. employ a lens of suitable focus fixed at one end of
a telescopic body in such a way that the image of the object required is thrown on
a disc of ground glass or other suitable material fixed within the telescopic body
itself, such image being viewed through an adjustable focussing eye-piece placed at
the opposite end of the telescopic body to that carrying the lens which throws the
image. The focussing of this image to be obtained by rack & pinion or other
suitable means such distance being registered on a scale attached.
As an alternate method an apparatus may be made of the ordinary telescope,
opera or field glass type provided with sufficient length of draw and with a scale
shewing the different distances. In this case the object is viewed direct, the inter-
vention of the disc of ground glass not being necessary.
Dated this 24th day of Anvil 1800
H. M. HASTINGS.
COMPLETE SPECIFICATION.
A New or Improved Apparatus for Ascertaining the Distance of any
Object for Photographic Purposes.
I, HENRY MITCHELL HASTINGS, of 54, Edith Road, West Kensington, Fulham,
London, W., Analytical Chemist, do hereby declare the nature of this invention and
in what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement :-
This invention relates to a telemeter or range finder particularly designed for
ascertaining the distance of an object to be photographed, in order that the photo-
graphic lens may be focussed by reference to a scale with sufficient accuracy to
produce a sharp image.
The instrument consists of a telescope having a semi-transparent screen on which
the image is thrown and viewed, and provided with a scale indicating the actual
distances of objects to which the various lengths of draw or distances between the
object and field glasses are proportional.
Reference is to be had to the accompanying drawings, forming part of this Speci-
fication, wherein
Figure 1 is a longitudinal section of the instrument and
Figure 2 is a separate view of the scale.
The instrument comprises the ordinary single or multiple draw telescopic
tube A A', object lens B, eye-piece lenses C and D of the kind known as a
Huyghenian or negative combination, and the semi-transparent screen E inter-
mediate of the field glass C and eye glass D at the focal point of the latter and at
such a distance from the field glass C that an image of the object will be thrown
on the screen E.
The lens D. which magnifies the image thrown on the screen, is adjustable,
to suit the vision of the observer, and having been first adjusted so that the grain

page_text: of the screen is perfectly sharp it is secured in that position by the clamping
screw d.
The distance between lenses B C is proportional to the actual distance of the
object whose image is focussed on the screen, and the tubes A' A are respectively
provided with an index f and scale F which is found or divided by actual trial at
known distances and is marked with the figures corresponding thereto, so that
when the image of an object at an unknown distance is clearly defined on the
screen E, the distance of the object may be ascertained by reference to the scale.
A similarly divided scale may be provided on the camera or instrument in connec-
tion with which the telemeter is intended to be used.
To facilitate the adjustment of the telemeter for the finer division corresponding
to the longer ranges and to expand the corresponding part of the scale, the tube A
has a slot of spiral form, as shewn, alongside of which the scale F is formed and in
which the index works, so that a combined turning and sliding motion is given
to the tube A' within the tube A.
Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
The herein described telemeter or range finder, consisting of a telescope provided
with a semi-transparent screen between the eye piece lenses, an adjustable eye lens,
and a scale indicating the various lengths of draw, corresponding to different
distances of objects viewed, substantially as specified.
Dated this 24th day of January 1991.
H. M. HASTINGS.
By A. M. & Wm. Clark,
53, Chancery Lane, London, Patent Agents.