<s>
A	O
stereoscope	B-Algorithm
is	O
a	O
device	O
for	O
viewing	O
a	O
stereoscopic	B-Algorithm
pair	I-Algorithm
of	O
separate	O
images	O
,	O
depicting	O
left-eye	O
and	O
right-eye	O
views	O
of	O
the	O
same	O
scene	O
,	O
as	O
a	O
single	O
three-dimensional	O
image	O
.	O
</s>
<s>
A	O
typical	O
stereoscope	B-Algorithm
provides	O
each	O
eye	O
with	O
a	O
lens	O
that	O
makes	O
the	O
image	O
seen	O
through	O
it	O
appear	O
larger	O
and	O
more	O
distant	O
and	O
usually	O
also	O
shifts	O
its	O
apparent	O
horizontal	O
position	O
,	O
so	O
that	O
for	O
a	O
person	O
with	O
normal	O
binocular	B-Algorithm
depth	O
perception	O
the	O
edges	O
of	O
the	O
two	O
images	O
seemingly	O
fuse	O
into	O
one	O
"	O
stereo	O
window	O
"	O
.	O
</s>
<s>
Most	O
people	O
can	O
,	O
with	O
practice	O
and	O
some	O
effort	O
,	O
view	O
stereoscopic	B-Algorithm
image	I-Algorithm
pairs	O
in	O
3D	O
without	O
the	O
aid	O
of	O
a	O
stereoscope	B-Algorithm
,	O
but	O
the	O
physiological	O
depth	O
cues	O
resulting	O
from	O
the	O
unnatural	O
combination	O
of	O
eye	O
convergence	O
and	O
focus	O
required	O
will	O
be	O
unlike	O
those	O
experienced	O
when	O
actually	O
viewing	O
the	O
scene	O
in	O
reality	O
,	O
making	O
an	O
accurate	O
simulation	O
of	O
the	O
natural	O
viewing	O
experience	O
impossible	O
and	O
tending	O
to	O
cause	O
eye	O
strain	O
and	O
fatigue	O
.	O
</s>
<s>
Although	O
more	O
recent	O
devices	O
such	O
as	O
Realist-format	B-Algorithm
3D	O
slide	O
viewers	O
,	O
the	O
View-Master	O
or	O
virtual	B-Device
reality	I-Device
headsets	I-Device
are	O
also	O
stereoscopes	B-Algorithm
,	O
the	O
word	O
is	O
now	O
most	O
commonly	O
associated	O
with	O
viewers	O
designed	O
for	O
the	O
standard-format	O
stereo	B-Algorithm
cards	I-Algorithm
that	O
enjoyed	O
several	O
waves	O
of	O
popularity	O
from	O
the	O
1850s	O
to	O
the	O
1930s	O
as	O
a	O
home	O
entertainment	O
medium	O
.	O
</s>
<s>
Devices	O
such	O
as	O
polarized	O
,	O
anaglyph	O
and	O
shutter	O
glasses	O
which	O
are	O
used	O
to	O
view	O
two	O
actually	O
superimposed	O
or	O
intermingled	O
images	O
,	O
rather	O
than	O
two	O
physically	O
separate	O
images	O
,	O
are	O
not	O
categorized	O
as	O
stereoscopes	B-Algorithm
.	O
</s>
<s>
The	O
earliest	O
stereoscopes	B-Algorithm
,	O
"	O
both	O
with	O
reflecting	O
mirrors	O
and	O
with	O
refracting	O
prisms	O
"	O
,	O
were	O
invented	O
by	O
Sir	O
Charles	O
Wheatstone	O
and	O
constructed	O
for	O
him	O
by	O
optician	O
R	O
.	O
Murray	O
in	O
1832	O
.	O
</s>
<s>
It	O
demonstrated	O
the	O
importance	O
of	O
binocular	B-Algorithm
depth	O
perception	O
by	O
showing	O
that	O
when	O
two	O
pictures	O
simulating	O
left-eye	O
and	O
right-eye	O
views	O
of	O
the	O
same	O
object	O
are	O
presented	O
so	O
that	O
each	O
eye	O
sees	O
only	O
the	O
image	O
designed	O
for	O
it	O
,	O
but	O
apparently	O
in	O
the	O
same	O
location	O
,	O
the	O
brain	O
will	O
fuse	O
the	O
two	O
and	O
accept	O
them	O
as	O
a	O
view	O
of	O
one	O
solid	O
three-dimensional	O
object	O
.	O
</s>
<s>
Wheatstone	O
's	O
stereoscope	B-Algorithm
was	O
introduced	O
in	O
the	O
year	O
before	O
the	O
first	O
practical	O
photographic	O
processes	O
became	O
available	O
,	O
so	O
initially	O
drawings	O
were	O
used	O
.	O
</s>
<s>
The	O
mirror	O
type	O
of	O
stereoscope	B-Algorithm
has	O
the	O
advantage	O
that	O
the	O
two	O
pictures	O
can	O
be	O
very	O
large	O
if	O
desired	O
.	O
</s>
<s>
Contrary	O
to	O
a	O
common	O
assertion	O
,	O
David	O
Brewster	O
did	O
not	O
invent	O
the	O
stereoscope	B-Algorithm
,	O
as	O
he	O
himself	O
was	O
often	O
at	O
pains	O
to	O
make	O
clear	O
.	O
</s>
<s>
A	O
rival	O
of	O
Wheatstone	O
,	O
Brewster	O
credited	O
the	O
invention	O
of	O
the	O
device	O
to	O
a	O
Mr.	O
Elliot	O
,	O
a	O
"	O
Teacher	O
of	O
Mathematics	O
"	O
from	O
Edinburgh	O
,	O
who	O
,	O
according	O
to	O
Brewster	O
,	O
conceived	O
of	O
the	O
idea	O
as	O
early	O
as	O
1823	O
and	O
,	O
in	O
1839	O
,	O
constructed	O
"	O
a	O
simple	O
stereoscope	B-Algorithm
without	O
lenses	O
or	O
mirrors	O
"	O
,	O
consisting	O
of	O
a	O
wooden	O
box	O
long	O
,	O
wide	O
and	O
high	O
,	O
which	O
was	O
used	O
to	O
view	O
drawn	O
landscape	O
transparencies	O
,	O
since	O
photography	O
had	O
yet	O
to	O
become	O
widespread	O
.	O
</s>
<s>
Brewster	O
's	O
personal	O
contribution	O
was	O
the	O
suggestion	O
to	O
use	O
lenses	O
for	O
uniting	O
the	O
dissimilar	O
pictures	O
in	O
1849	O
;	O
and	O
accordingly	O
the	O
lenticular	O
stereoscope	B-Algorithm
(	O
lens-based	O
)	O
may	O
fairly	O
be	O
said	O
to	O
be	O
his	O
invention	O
.	O
</s>
<s>
This	O
allowed	O
a	O
reduction	O
in	O
size	O
,	O
creating	O
hand-held	O
devices	O
,	O
which	O
became	O
known	O
as	O
Brewster	O
Stereoscopes	B-Algorithm
,	O
much	O
admired	O
by	O
Queen	O
Victoria	O
when	O
they	O
were	O
demonstrated	O
at	O
the	O
Great	O
Exhibition	O
of	O
1851	O
.	O
</s>
<s>
Brewster	O
was	O
unable	O
to	O
find	O
in	O
Britain	O
an	O
instrument	O
maker	O
capable	O
of	O
working	O
with	O
his	O
design	O
,	O
so	O
he	O
took	O
it	O
to	O
France	O
,	O
where	O
the	O
stereoscope	B-Algorithm
was	O
improved	O
by	O
Jules	O
Duboscq	O
who	O
made	O
stereoscopes	B-Algorithm
and	O
stereoscopic	B-Algorithm
daguerreotypes	O
,	O
and	O
a	O
famous	O
picture	O
of	O
Queen	O
Victoria	O
that	O
was	O
displayed	O
at	O
The	O
Great	O
Exhibition	O
.	O
</s>
<s>
Almost	O
overnight	O
a	O
3D	O
industry	O
developed	O
and	O
250,000	O
stereoscopes	B-Algorithm
were	O
produced	O
and	O
a	O
great	O
number	O
of	O
stereoviews	B-Algorithm
,	O
stereo	B-Algorithm
cards	I-Algorithm
,	O
stereo	O
pairs	O
or	O
stereographs	B-Algorithm
were	O
sold	O
in	O
a	O
short	O
time	O
.	O
</s>
<s>
Stereographers	O
were	O
sent	O
throughout	O
the	O
world	O
to	O
capture	O
views	O
for	O
the	O
new	O
medium	O
and	O
feed	O
the	O
demand	O
for	O
3D	B-Algorithm
images	I-Algorithm
.	O
</s>
<s>
The	O
stereoscope	B-Algorithm
,	O
which	O
dates	O
from	O
the	O
1850s	O
,	O
consisted	O
of	O
two	O
prismatic	O
lenses	O
and	O
a	O
wooden	O
stand	O
to	O
hold	O
the	O
stereo	B-Algorithm
card	I-Algorithm
.	O
</s>
<s>
This	O
type	O
of	O
stereoscope	B-Algorithm
remained	O
in	O
production	O
for	O
a	O
century	O
and	O
there	O
are	O
still	O
companies	O
making	O
them	O
in	O
limited	O
production	O
currently	O
.	O
</s>
<s>
Multiple	O
view	O
stereoscopes	B-Algorithm
allow	O
viewing	O
multiple	O
stereoscopic	B-Algorithm
images	I-Algorithm
in	O
sequence	O
by	O
turning	O
a	O
knob	O
,	O
crank	O
or	O
pushing	O
down	O
a	O
lever	O
.	O
</s>
<s>
The	O
belt	O
can	O
usually	O
hold	O
50	O
paper	O
card	O
or	O
glass	O
stereoviews	B-Algorithm
,	O
but	O
there	O
are	O
also	O
large	O
floor	O
standing	O
models	O
for	O
100	O
or	O
200	O
views	O
.	O
</s>
<s>
A	O
more	O
advanced	O
multiple	O
view	O
stereoscope	B-Algorithm
is	O
only	O
intended	O
for	O
glass	O
slides	O
and	O
was	O
especially	O
popular	O
in	O
France	O
,	O
as	O
the	O
printing	O
of	O
stereo	O
images	O
on	O
glass	O
was	O
a	O
French	O
specialty	O
and	O
popular	O
until	O
the	O
1930s	O
.	O
</s>
<s>
In	O
the	O
mid-20th	O
century	O
the	O
View-Master	O
stereoscope	B-Algorithm
(	O
patented	O
1939	O
)	O
,	O
with	O
its	O
rotating	O
cardboard	O
disks	O
containing	O
image	O
pairs	O
,	O
was	O
popular	O
first	O
for	O
'	O
virtual	O
tourism	O
 '	O
and	O
then	O
as	O
a	O
toy	O
.	O
</s>
<s>
In	O
2010	O
,	O
Hasbro	O
started	O
producing	O
a	O
stereoscope	B-Algorithm
designed	O
to	O
hold	O
an	O
iPhone	O
or	O
iPod	O
Touch	O
,	O
called	O
the	O
My3D	O
.	O
</s>
<s>
In	O
2014	O
,	O
Google	B-Application
released	O
the	O
template	O
for	O
a	O
papercraft	O
stereoscope	B-Algorithm
called	O
Google	B-Device
Cardboard	I-Device
.	O
</s>
<s>
Apps	O
on	O
the	O
mobile	O
phone	O
substitute	O
for	O
stereo	B-Algorithm
cards	I-Algorithm
;	O
these	O
apps	O
can	O
also	O
sense	O
rotation	O
and	O
expand	O
the	O
stereoscope	B-Algorithm
's	O
capacity	O
into	O
that	O
of	O
a	O
full-fledged	O
virtual	B-Application
reality	I-Application
device	O
.	O
</s>
<s>
The	O
underlying	O
technology	O
is	O
otherwise	O
unchanged	O
from	O
earlier	O
stereoscopes	B-Algorithm
.	O
</s>
<s>
Several	O
fine	O
arts	O
photographers	O
and	O
graphic	O
artists	O
have	O
and	O
continue	O
to	O
produce	O
original	O
artwork	O
to	O
be	O
viewed	O
using	O
stereoscopes	B-Algorithm
.	O
</s>
<s>
A	O
simple	O
stereoscope	B-Algorithm
is	O
limited	O
in	O
the	O
size	O
of	O
the	O
image	O
that	O
may	O
be	O
used	O
.	O
</s>
<s>
A	O
more	O
complex	O
stereoscope	B-Algorithm
uses	O
a	O
pair	O
of	O
horizontal	O
periscope-like	O
devices	O
,	O
allowing	O
the	O
use	O
of	O
larger	O
images	O
that	O
can	O
present	O
more	O
detailed	O
information	O
in	O
a	O
wider	O
field	O
of	O
view	O
.	O
</s>
<s>
The	O
stereoscope	B-Algorithm
is	O
essentially	O
an	O
instrument	O
in	O
which	O
two	O
photographs	O
of	O
the	O
same	O
object	O
,	O
taken	O
from	O
slightly	O
different	O
angles	O
,	O
are	O
simultaneously	O
presented	O
,	O
one	O
to	O
each	O
eye	O
.	O
</s>
<s>
A	O
moving	O
image	O
extension	O
of	O
the	O
stereoscope	B-Algorithm
has	O
a	O
large	O
vertically	O
mounted	O
drum	O
containing	O
a	O
wheel	O
upon	O
which	O
are	O
mounted	O
a	O
series	O
of	O
stereographic	B-Algorithm
cards	I-Algorithm
which	O
form	O
a	O
moving	O
picture	O
.	O
</s>
<s>
The	O
stereoscope	B-Algorithm
offers	O
several	O
advantages	O
:	O
</s>
<s>
A	O
stereo	O
transparency	O
viewer	O
is	O
a	O
type	O
of	O
stereoscope	B-Algorithm
that	O
offers	O
similar	O
advantages	O
,	O
e.g.	O
</s>
<s>
Disadvantages	O
of	O
stereo	B-Algorithm
cards	I-Algorithm
,	O
slides	O
or	O
any	O
other	O
hard	O
copy	O
or	O
print	O
are	O
that	O
the	O
two	O
images	O
are	O
likely	O
to	O
receive	O
differing	O
wear	O
,	O
scratches	O
and	O
other	O
decay	O
.	O
</s>
