<s>
A	O
projector	B-Application
or	O
image	B-Application
projector	I-Application
is	O
an	O
optical	O
device	O
that	O
projects	O
an	O
image	O
(	O
or	O
moving	O
images	O
)	O
onto	O
a	O
surface	O
,	O
commonly	O
a	O
projection	O
screen	O
.	O
</s>
<s>
Most	O
projectors	B-Application
create	O
an	O
image	O
by	O
shining	O
a	O
light	O
through	O
a	O
small	O
transparent	O
lens	O
,	O
but	O
some	O
newer	O
types	O
of	O
projectors	B-Application
can	O
project	O
the	O
image	O
directly	O
,	O
by	O
using	O
lasers	O
.	O
</s>
<s>
A	O
virtual	B-General_Concept
retinal	I-General_Concept
display	I-General_Concept
,	O
or	O
retinal	B-General_Concept
projector	I-General_Concept
,	O
is	O
a	O
projector	B-Application
that	O
projects	O
an	O
image	O
directly	O
on	O
the	O
retina	O
instead	O
of	O
using	O
an	O
external	O
projection	O
screen	O
.	O
</s>
<s>
The	O
most	O
common	O
type	O
of	O
projector	B-Application
used	O
today	O
is	O
called	O
a	O
video	B-Device
projector	I-Device
.	O
</s>
<s>
Video	B-Device
projectors	I-Device
are	O
digital	O
replacements	O
for	O
earlier	O
types	O
of	O
projectors	B-Application
such	O
as	O
slide	B-Device
projectors	I-Device
and	O
overhead	B-Device
projectors	I-Device
.	O
</s>
<s>
These	O
earlier	O
types	O
of	O
projectors	B-Application
were	O
mostly	O
replaced	O
with	O
digital	B-Device
video	I-Device
projectors	I-Device
throughout	O
the	O
1990s	O
and	O
early	O
2000s	O
,	O
but	O
old	O
analog	O
projectors	B-Application
are	O
still	O
used	O
at	O
some	O
places	O
.	O
</s>
<s>
The	O
newest	O
types	O
of	O
projectors	B-Application
are	O
handheld	B-General_Concept
projectors	I-General_Concept
that	O
use	O
lasers	O
or	O
LEDs	O
to	O
project	O
images	O
.	O
</s>
<s>
Movie	O
theaters	O
used	O
a	O
type	O
of	O
projector	B-Application
called	O
a	O
movie	B-Application
projector	I-Application
,	O
nowadays	O
mostly	O
replaced	O
with	O
digital	O
cinema	O
video	B-Device
projectors	I-Device
.	O
</s>
<s>
Projectors	B-Application
can	O
be	O
roughly	O
divided	O
into	O
three	O
categories	O
,	O
based	O
on	O
the	O
type	O
of	O
input	O
.	O
</s>
<s>
Some	O
of	O
the	O
listed	O
projectors	B-Application
were	O
capable	O
of	O
projecting	O
several	O
types	O
of	O
input	O
.	O
</s>
<s>
For	O
instance	O
:	O
video	B-Device
projectors	I-Device
were	O
basically	O
developed	O
for	O
the	O
projection	O
of	O
prerecorded	O
moving	O
images	O
,	O
but	O
are	O
regularly	O
used	O
for	O
still	O
images	O
in	O
PowerPoint	B-Application
presentations	O
and	O
can	O
easily	O
be	O
connected	O
to	O
a	O
video	O
camera	O
for	O
real-time	O
input	O
.	O
</s>
<s>
The	O
magic	B-Device
lantern	I-Device
is	O
best	O
known	O
for	O
the	O
projection	O
of	O
still	O
images	O
,	O
but	O
was	O
capable	O
of	O
projecting	O
moving	O
images	O
from	O
mechanical	O
slides	O
since	O
its	O
invention	O
and	O
was	O
probably	O
at	O
its	O
peak	O
of	O
popularity	O
when	O
used	O
in	O
phantasmagoria	B-Application
shows	O
to	O
project	O
moving	O
images	O
of	O
ghosts	O
.	O
</s>
<s>
There	O
probably	O
existed	O
quite	O
a	O
few	O
other	O
types	O
of	O
projectors	B-Application
than	O
the	O
examples	O
described	O
below	O
,	O
but	O
evidence	O
is	O
scarce	O
and	O
reports	O
are	O
often	O
unclear	O
about	O
their	O
nature	O
.	O
</s>
<s>
Spectators	O
did	O
not	O
always	O
provide	O
the	O
details	O
needed	O
to	O
differentiate	O
between	O
for	O
instance	O
a	O
shadow	O
play	O
and	O
a	O
lantern	B-Device
projection	I-Device
.	O
</s>
<s>
Shadow	O
play	O
usually	O
does	O
not	O
involve	O
a	O
projection	O
device	O
,	O
but	O
can	O
be	O
seen	O
as	O
a	O
first	O
step	O
in	O
the	O
development	O
of	O
projectors	B-Application
.	O
</s>
<s>
Projectors	B-Application
share	O
a	O
common	O
history	O
with	O
cameras	O
in	O
the	O
camera	B-Algorithm
obscura	I-Algorithm
.	O
</s>
<s>
Camera	B-Algorithm
obscura	I-Algorithm
(	O
Latin	O
for	O
"	O
dark	O
room	O
"	O
)	O
is	O
the	O
natural	O
optical	O
phenomenon	O
that	O
occurs	O
when	O
an	O
image	O
of	O
a	O
scene	O
at	O
the	O
other	O
side	O
of	O
a	O
screen	O
(	O
or	O
for	O
instance	O
a	O
wall	O
)	O
is	O
projected	O
through	O
a	O
small	O
hole	O
in	O
that	O
screen	O
to	O
form	O
an	O
inverted	O
image	O
(	O
left	O
to	O
right	O
and	O
upside	O
down	O
)	O
on	O
a	O
surface	O
opposite	O
to	O
the	O
opening	O
.	O
</s>
<s>
Mozi	O
correctly	O
asserted	O
that	O
the	O
camera	B-Algorithm
obscura	I-Algorithm
image	O
is	O
inverted	O
because	O
light	O
travels	O
in	O
straight	O
lines	O
.	O
</s>
<s>
In	O
1437	O
Italian	O
humanist	O
author	O
,	O
artist	O
,	O
architect	O
,	O
poet	O
,	O
priest	O
,	O
linguist	O
,	O
philosopher	O
and	O
cryptographer	O
Leon	O
Battista	O
Alberti	O
is	O
thought	O
to	O
have	O
possibly	O
projected	O
painted	O
pictures	O
from	O
a	O
small	O
closed	O
box	O
with	O
a	O
small	O
hole	O
,	O
but	O
it	O
is	O
unclear	O
whether	O
this	O
actually	O
was	O
a	O
projector	B-Application
or	O
rather	O
a	O
type	O
of	O
show	O
box	O
with	O
transparent	O
pictures	O
illuminated	O
from	O
behind	O
and	O
viewed	O
through	O
the	O
hole	O
.	O
</s>
<s>
Leonardo	B-Application
da	I-Application
Vinci	I-Application
is	O
thought	O
to	O
have	O
had	O
a	O
projecting	O
lantern	O
-	O
with	O
a	O
condensing	O
lens	O
,	O
candle	O
and	O
chimney	O
-	O
based	O
on	O
a	O
small	O
sketch	O
from	O
around	O
1515	O
.	O
</s>
<s>
Dutch	O
inventor	O
Cornelis	O
Drebbel	O
,	O
who	O
is	O
a	O
likely	O
inventor	O
of	O
the	O
microscope	O
,	O
is	O
thought	O
to	O
have	O
had	O
some	O
kind	O
of	O
projector	B-Application
that	O
he	O
used	O
in	O
magical	O
performances	O
.	O
</s>
<s>
The	O
letter	O
was	O
found	O
in	O
the	O
papers	O
of	O
his	O
friend	O
Constantijn	O
Huygens	O
,	O
father	O
of	O
the	O
likely	O
inventor	O
of	O
the	O
magic	B-Device
lantern	I-Device
Christiaan	O
Huygens	O
.	O
</s>
<s>
The	O
book	O
was	O
quite	O
influential	O
and	O
inspired	O
many	O
scholars	O
,	O
probably	O
including	O
Christiaan	O
Huygens	O
who	O
would	O
invent	O
the	O
magic	B-Device
lantern	I-Device
.	O
</s>
<s>
Kircher	O
was	O
often	O
credited	O
as	O
the	O
inventor	O
of	O
the	O
magic	B-Device
lantern	I-Device
,	O
although	O
in	O
his	O
1671	O
edition	O
of	O
Ars	O
Magna	O
Lucis	O
et	O
Umbrae	O
Kircher	O
himself	O
credited	O
Danish	O
mathematician	O
Thomas	O
Rasmussen	O
Walgensten	O
for	O
the	O
magic	B-Device
lantern	I-Device
,	O
which	O
Kircher	O
saw	O
as	O
a	O
further	O
development	O
of	O
his	O
own	O
projection	O
system	O
.	O
</s>
<s>
It	O
is	O
sometimes	O
reported	O
that	O
Martini	O
lectured	O
throughout	O
Europe	O
with	O
a	O
magic	B-Device
lantern	I-Device
which	O
he	O
might	O
have	O
imported	O
from	O
China	O
,	O
but	O
there	O
's	O
no	O
evidence	O
that	O
anything	O
other	O
than	O
Kircher	O
's	O
technique	O
was	O
used	O
.	O
</s>
<s>
By	O
1659	O
Dutch	O
scientist	O
Christiaan	O
Huygens	O
had	O
developed	O
the	O
magic	B-Device
lantern	I-Device
,	O
which	O
used	O
a	O
concave	O
mirror	O
to	O
reflect	O
and	O
direct	O
as	O
much	O
of	O
the	O
light	O
of	O
a	O
lamp	O
as	O
possible	O
through	O
a	O
small	O
sheet	O
of	O
glass	O
on	O
which	O
was	O
the	O
image	O
to	O
be	O
projected	O
,	O
and	O
onward	O
into	O
a	O
focusing	O
lens	O
at	O
the	O
front	O
of	O
the	O
apparatus	O
to	O
project	O
the	O
image	O
onto	O
a	O
wall	O
or	O
screen	O
(	O
Huygens	O
apparatus	O
actually	O
used	O
two	O
additional	O
lenses	O
)	O
.	O
</s>
<s>
The	O
magic	B-Device
lantern	I-Device
became	O
a	O
very	O
popular	O
medium	O
for	O
entertainment	O
and	O
educational	O
purposes	O
in	O
the	O
18th	O
and	O
19th	O
century	O
.	O
</s>
<s>
The	O
magic	B-Device
lantern	I-Device
remained	O
a	O
common	O
medium	O
until	O
slide	B-Device
projectors	I-Device
came	O
into	O
widespread	O
use	O
during	O
the	O
1950s	O
.	O
</s>
<s>
A	O
few	O
years	O
before	O
his	O
death	O
in	O
1736	O
Polish-German-Dutch	O
physicist	O
Daniel	O
Gabriel	O
Fahrenheit	O
reportedly	O
constructed	O
a	O
solar	O
microscope	O
,	O
which	O
basically	O
was	O
a	O
combination	O
of	O
the	O
compound	O
microscope	O
with	O
camera	B-Algorithm
obscura	I-Algorithm
projection	O
.	O
</s>
<s>
Swiss	O
mathematician	O
,	O
physicist	O
,	O
astronomer	O
,	O
logician	O
and	O
engineer	O
Leonhard	O
Euler	O
demonstrated	O
an	O
opaque	B-General_Concept
projector	I-General_Concept
,	O
now	O
commonly	O
known	O
as	O
an	O
episcope	O
,	O
around	O
1756	O
.	O
</s>
<s>
Around	O
1872	O
Henry	O
Morton	O
used	O
an	O
opaque	B-General_Concept
projector	I-General_Concept
in	O
demonstrations	O
for	O
huge	O
audiences	O
,	O
for	O
example	O
in	O
the	O
Philadelphia	O
Opera	O
House	O
which	O
could	O
seat	O
3500	O
people	O
.	O
</s>
<s>
In	O
the	O
early	O
and	O
middle	O
parts	O
of	O
the	O
20th	O
century	O
,	O
low-cost	O
opaque	B-General_Concept
projectors	I-General_Concept
were	O
produced	O
and	O
marketed	O
as	O
a	O
toy	O
for	O
children	O
.	O
</s>
<s>
The	O
light	O
source	O
in	O
early	O
opaque	B-General_Concept
projectors	I-General_Concept
was	O
often	O
limelight	O
,	O
with	O
incandescent	O
light	O
bulbs	O
and	O
halogen	O
lamps	O
taking	O
over	O
later	O
.	O
</s>
<s>
In	O
the	O
late	O
1950s	O
and	O
early	O
1960s	O
,	O
overhead	B-Device
projectors	I-Device
began	O
to	O
be	O
widely	O
used	O
in	O
schools	O
and	O
businesses	O
.	O
</s>
<s>
The	O
first	O
overhead	B-Device
projector	I-Device
was	O
used	O
for	O
police	O
identification	O
work	O
.	O
</s>
<s>
From	O
the	O
1950s	O
to	O
the	O
1990s	O
slide	B-Device
projectors	I-Device
for	O
35	O
mm	O
photographic	O
positive	O
film	B-Device
slides	I-Device
were	O
common	O
for	O
presentations	O
and	O
as	O
a	O
form	O
of	O
entertainment	O
;	O
family	O
members	O
and	O
friends	O
would	O
occasionally	O
gather	O
to	O
view	O
slideshows	O
,	O
typically	O
of	O
vacation	O
travels	O
.	O
</s>
<s>
Complex	O
Multi-image	O
shows	O
of	O
the	O
1970s	O
to	O
1990s	O
,	O
purposed	O
usually	O
for	O
marketing	O
,	O
promotion	O
or	O
community	O
service	O
or	O
artistic	O
displays	O
,	O
used	O
35mm	O
and	O
46mm	O
transparency	O
slides	O
(	O
diapositives	O
)	O
projected	O
by	O
single	O
or	O
multiple	O
slide	B-Device
projectors	I-Device
onto	O
one	O
or	O
more	O
screens	O
in	O
synchronization	O
with	O
an	O
audio	O
voice-over	O
and/or	O
music	O
track	O
controlled	O
by	O
a	O
pulsed-signal	O
tape	O
or	O
cassette	O
.	O
</s>
<s>
Digital	B-Application
cameras	I-Application
had	O
become	O
commercialised	O
by	O
1990	O
,	O
and	O
in	O
1997	O
Microsoft	B-Application
PowerPoint	I-Application
was	O
updated	O
to	O
include	O
image	O
files	O
,	O
accelerating	O
the	O
transition	O
from	O
35	O
mm	O
slides	O
to	O
digital	O
images	O
,	O
and	O
thus	O
digital	B-Device
projectors	I-Device
,	O
in	O
pedagogy	O
and	O
training	O
.	O
</s>
<s>
Production	O
of	O
all	O
Kodak	O
Carousel	O
slide	B-Device
projectors	I-Device
ceased	O
in	O
2004	O
,	O
and	O
in	O
2009	O
manufacture	O
and	O
processing	O
of	O
Kodachrome	O
film	O
was	O
discontinued	O
.	O
</s>
<s>
In	O
Mad	O
Men	O
's	O
first	O
series	O
the	O
final	O
episode	O
presents	O
the	O
protagonist	O
Don	O
Draper	O
's	O
presentation	O
(	O
via	O
slide	B-Device
projector	I-Device
)	O
of	O
a	O
plan	O
to	O
market	O
the	O
Kodak	O
slide	O
carrier	O
a	O
'	O
carousel	O
 '	O
.	O
</s>
