Improvements in Telescopic Fronts for Optical Lanterns.
Year: 1889

page_text: Date of Application, 7th May, 1889
Complete Specification Left, 22nd May, 1889-Accepted, 13th July, 1889
PROVISIONAL SPECIFICATION.
Improvements in Telescopic Fronts for Optical Lanterns.
I, ALFRED WRENCH, of 50, Grays Inn Road, in the county of London, Optician,
do hereby declare the nature of this invention to be as follows
1
My invention relates to telescopic fronts, of the kind described in the specification
of former Letters Patent granted to me dated A.D. 1887. 31st October,
No 14809, for enabling optical lanterns to be used with lenses or objectives of
varying focus.
The chief object of my present invention is to provide a telescopic front which is
both simpler in construction and cheaper than that described in the Specification
before referred, and to this end it comprises the improvements hereinafter described.
In carrying out my invention I provide a series of two or more tubes adapted to
slide one within the other, the inner end of the outer tube being constructed to fit
into, or be secured to, the body of the lantern, and the outer end of the inner tube
to carry a lens or objective, all in a well known manner.
The said tubes, instead of being provided with racks and pinions for adjusting
them, as described in the specification before mentioned, are adapted to be approxi-
mately adjusted by hand, the fine adjustment being effected by means of the lens
rack.
To prevent any accidental displacement of the tubes and to ensure their axial
alignment when extended, 1 provide for clamping the end portion of each tube upon
the tube sliding within it For this purpose the outermost end of each tube (with
the exception of the inner tube carrying the lens) is screw threaded externally and
made slightly tapering, and upon it is placed an internally screw threaded collar or
a nut which is correspondingly tapered The result of this arrangement is that when
the collar or nut is tightened upon its thread it will tend to contract the tube and so
reduce its diameter at the end portion. A number of saw-cuts or slots are formed
in the said screwed end portion, to enable it to be readily contracted and clamped
upon the tube within it
In order to prevent the tubes from being inadvertently separated, a set screw is
advantageously placed in the larger tube, its end extending into slots formed in
the tube within it.
I wish it understood that I do not confine myself to the means hereinbefore
described for contracting the ends of the tubes, as it is obvious that the same can
be considerably modified, for instance, the screw threads on the ends of the tubes
and within the collars can be dispensed with, the said collars being fixed by means
of bayonet joint, or by means of pins attached to the tubes and working in inclined
slots or grooves in the collars or vice versa, that is to say, the pins being attached to the
collars and entering slots formed in the tubes.
G. F. REDFERN & Co.,
, 4, South Street, Finsbury, London, Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in Telescopic Fronts for Optical Lanterns.
I, ALFRED WRENCH, of 50), Grays Inn Road, in the County of London, Optician,
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:-
My invention relates to telescopic fronts, of the kind described in the specification

page_text: of former Letters Patent granted to me dated AD 1887, 31st October'
No 14809, for enabling optical lanterns to be used with lenses or objectives of
varying focus.
The chief object of my present invention is to provide a telescopic front which is
both simpler in construction and cheaper than that described in the specification
before referred to, and to this end it comprises the improvements hereinafter described
In carrying out my invention I provide a series of two or more tubes adapted
to slide one within the other, the inner end of the outer tube being constructed to
fit into, or be secured to the body of the lantern, and the outer end of the inner
tube to carry a lens or objective, all in a well known manner
The said tubes, instead of being provided with racks and pinions for adjusting
them as described in the specification before mentioned, are adapted to be approxi-
mately adjusted by hand, the fine adjustment being effected by means of the lens
rack, and to prevent any accidental displacement of the tubes and to ensure their
axial alignment when extended, I provide for clamping the end portion of each
tube upon the tube sliding within it, all as hereinafter described
In the accompanying drawing-
Figure 1 is a longitudinal section of a telescopic-front provided with my improvements.
Figure 2 is a side elevation of a portion of one of the tubes; and,
Figure 3 is a view of a detail
وو
a, a, a are three tubes, which are adapted to slide one within the other in a
well known manner the tube a being provided with the flange b for securing the
"front
to the body of the lantern, and the tube a with the plate for carrying the
lens or objective The outer end of each of the tubes a, a¹ is provided with a series
of saw-cuts d, d, to enable the said ends to be readily contracted and clamped
upon the tubes within them, and adjacent to the said saw-cuts are formed screw-
threads e, e
ffare collars, which are at one side internally screw threaded to fit upon the
screw threads e, e, but which at the other side are made slightly conical, and adapted
to fit upon the correspondingly tapered ends of the tubes a, a', in such a manner
that if the said collars f, fare screwed upon the said tubes, the ends of the latter will
be contracted
9, 9 are handles, which are formed on, or secured to the rings f, f for operating
the same.
h is a pin attached to the tube a¹ and entering a slot in the tube a³, and is a set
screw in the tubo a entering a slot in the tube a¹, the said pin and set screw
preventing the said tubes from being inadvertently separated
I sometimes modify the construction hereinbefore described, by forming the
screw threads upon the tapering end portions of the tubes a, a¹, this arrangement
however is not so advantageous as that herembefore described, owing to the fact
that the said screw threads formed within the collar occasionally get across those on
the tubes; also, instead of using the screw threads e, e, 1 can attach pins to the
tubes a, a and provide the collars f, f with extensions, in which are formed inclined
grooves adapted to engage with the said pins Or the collars may be connected to
the tubes by bayonet joints
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. A telescopic front for optical lanterns, the tubes of which are designed to be
adjusted without the intervention of racks and pinions, or other mechanism, and
which are fixed relatively to each other, by clamping the outer end of each tube
upon that sliding within it, substantially as described.
2 In a telescopic front for optical lanterns, the employment of an internally
tapered collar adapted to be screwed or otherwise tightened upon the corre-
spondingly tapered end of such external tube for clamping the same upon the tube
sliding within it, substantially as described

page_text: 3. The manufacture and use of the improved telescopic-front hereinbefore described
and illustrated in the accompanying drawing.
Dated the 22nd May 1889.
G. F. REDFERN & Co.,
4, South Street. Finsbury, London, Agents for the Applicant.