<s>
A	O
single-lens	B-Algorithm
reflex	I-Algorithm
camera	I-Algorithm
(	O
SLR	B-Algorithm
)	O
is	O
a	O
camera	O
that	O
typically	O
uses	O
a	O
mirror	O
and	O
prism	O
system	O
(	O
hence	O
"	O
reflex	O
"	O
from	O
the	O
mirror	O
's	O
reflection	O
)	O
that	O
permits	O
the	O
photographer	O
to	O
view	O
through	O
the	O
lens	O
and	O
see	O
exactly	O
what	O
will	O
be	O
captured	O
.	O
</s>
<s>
With	O
twin	B-Algorithm
lens	I-Algorithm
reflex	I-Algorithm
and	O
rangefinder	B-Algorithm
cameras	I-Algorithm
,	O
the	O
viewed	O
image	O
could	O
be	O
significantly	O
different	O
from	O
the	O
final	O
image	O
.	O
</s>
<s>
When	O
the	O
shutter	B-Algorithm
button	O
is	O
pressed	O
on	O
most	O
SLRs	B-Algorithm
,	O
the	O
mirror	O
flips	O
out	O
of	O
the	O
light	O
path	O
,	O
allowing	O
light	O
to	O
pass	O
through	O
to	O
the	O
light	O
receptor	O
and	O
the	O
image	O
to	O
be	O
captured	O
.	O
</s>
<s>
Prior	O
to	O
the	O
development	O
of	O
SLR	B-Algorithm
,	O
all	O
cameras	O
with	O
viewfinders	O
had	O
two	O
optical	O
light	O
paths	O
:	O
one	O
path	O
through	O
the	O
lens	O
to	O
the	O
film	O
,	O
and	O
another	O
path	O
positioned	O
above	O
(	O
TLR	O
or	O
twin-lens	B-Algorithm
reflex	I-Algorithm
)	O
or	O
to	O
the	O
side	O
(	O
rangefinder	B-Algorithm
)	O
.	O
</s>
<s>
This	O
is	O
not	O
problematic	O
for	O
pictures	O
taken	O
at	O
a	O
middle	O
or	O
longer	O
distance	O
,	O
but	O
parallax	B-Device
causes	O
framing	O
errors	O
in	O
close-up	O
shots	O
.	O
</s>
<s>
Moreover	O
,	O
focusing	O
the	O
lens	O
of	O
a	O
fast	O
reflex	O
camera	O
when	O
it	O
is	O
opened	O
to	O
wider	O
apertures	B-General_Concept
(	O
such	O
as	O
in	O
low	O
light	O
or	O
while	O
using	O
low-speed	O
film	O
)	O
is	O
not	O
easy	O
.	O
</s>
<s>
Most	O
SLR	B-Algorithm
cameras	I-Algorithm
permit	O
upright	O
and	O
laterally	O
correct	O
viewing	O
through	O
use	O
of	O
a	O
roof	O
pentaprism	O
situated	O
in	O
the	O
optical	O
path	O
between	O
the	O
reflex	O
mirror	O
and	O
viewfinder	O
.	O
</s>
<s>
When	O
the	O
shutter	B-Algorithm
is	O
released	O
,	O
the	O
mirror	O
moves	O
out	O
of	O
the	O
light	O
path	O
,	O
and	O
the	O
light	O
shines	O
directly	O
onto	O
the	O
film	O
(	O
or	O
in	O
the	O
case	O
of	O
a	O
DSLR	B-Device
,	O
the	O
CCD	B-Algorithm
or	O
CMOS	B-Device
imaging	O
sensor	B-Algorithm
)	O
.	O
</s>
<s>
The	O
Canon	B-Algorithm
Pellix	I-Algorithm
,	O
along	O
with	O
several	O
special	O
purpose	O
high	O
speed	O
cameras(such as the Canon EOS-1N RS )	O
,	O
were	O
an	O
exception	O
to	O
the	O
moving	O
mirror	O
system	O
,	O
wherein	O
the	O
mirror	O
was	O
a	O
fixed	O
beamsplitting	O
pellicle	B-Algorithm
.	O
</s>
<s>
Up	O
until	O
the	O
1990s	O
,	O
SLR	B-Algorithm
was	O
the	O
most	O
advanced	O
photographic	O
preview	O
system	O
available	O
,	O
but	O
the	O
recent	O
development	O
and	O
refinement	O
of	O
digital	O
imaging	O
technology	O
with	O
an	O
on-camera	O
live	O
LCD	B-Device
preview	O
screen	O
has	O
overshadowed	O
SLR	B-Algorithm
's	O
popularity	O
.	O
</s>
<s>
Nearly	O
all	O
inexpensive	O
compact	O
digital	O
cameras	O
now	O
include	O
an	O
LCD	B-Device
preview	O
screen	O
allowing	O
the	O
photographer	O
to	O
see	O
what	O
the	O
CCD	B-Algorithm
is	O
capturing	O
.	O
</s>
<s>
However	O
,	O
SLR	B-Algorithm
is	O
still	O
popular	O
in	O
high-end	O
and	O
professional	O
cameras	O
because	O
they	O
are	O
system	B-Algorithm
cameras	I-Algorithm
with	O
interchangeable	O
parts	O
,	O
allowing	O
customization	O
.	O
</s>
<s>
They	O
also	O
have	O
far	O
less	O
shutter	B-Algorithm
lag	O
,	O
allowing	O
photographs	O
to	O
be	O
timed	O
more	O
precisely	O
.	O
</s>
<s>
Also	O
the	O
pixel	B-Algorithm
resolution	O
,	O
contrast	O
ratio	O
,	O
refresh	O
rate	O
,	O
and	O
color	O
gamut	O
of	O
an	O
LCD	B-Device
preview	O
screen	O
cannot	O
compete	O
with	O
the	O
clarity	O
and	O
shadow	O
detail	O
of	O
a	O
direct-viewed	O
optical	O
SLR	B-Algorithm
viewfinder	O
.	O
</s>
<s>
Large	O
format	O
SLR	B-Algorithm
cameras	I-Algorithm
were	O
probably	O
first	O
marketed	O
with	O
the	O
introduction	O
of	O
C.R.	O
</s>
<s>
SLRs	B-Algorithm
for	O
smaller	O
exposure	O
formats	O
were	O
launched	O
in	O
the	O
1920s	O
by	O
several	O
camera	O
makers	O
.	O
</s>
<s>
The	O
first	O
35	O
mm	O
SLR	B-Algorithm
available	O
to	O
the	O
mass	O
market	O
,	O
Leica	O
's	O
PLOOT	O
reflex	O
housing	O
along	O
with	O
a	O
200mm	O
f4.5	O
lens	O
paired	O
to	O
a	O
35	O
mm	O
rangefinder	B-Algorithm
camera	I-Algorithm
body	O
,	O
debuted	O
in	O
1935	O
.	O
</s>
<s>
K	O
.	O
Nüchterlein	O
's	O
Kine	B-Algorithm
Exakta	I-Algorithm
(	O
Germany	O
,	O
1936	O
)	O
was	O
the	O
first	O
integrated	O
35	O
mm	O
SLR	B-Algorithm
to	O
enter	O
the	O
market	O
.	O
</s>
<s>
Additional	O
Exakta	O
models	O
,	O
all	O
with	O
waist-level	B-Algorithm
finders	I-Algorithm
,	O
were	O
produced	O
up	O
to	O
and	O
during	O
World	O
War	O
II	O
.	O
</s>
<s>
Another	O
ancestor	O
of	O
the	O
modern	O
SLR	B-Algorithm
camera	I-Algorithm
was	O
the	O
Swiss-made	O
Alpa	O
,	O
which	O
was	O
innovative	O
,	O
and	O
influenced	O
the	O
later	O
Japanese	O
cameras	O
.	O
</s>
<s>
The	O
first	O
eye-level	O
SLR	B-Algorithm
viewfinder	O
was	O
patented	O
in	O
Hungary	O
on	O
August	O
23	O
,	O
1943	O
,	O
by	O
Jenő	O
Dulovits	O
,	O
who	O
then	O
designed	O
the	O
first	O
35mm	O
camera	O
with	O
one	O
,	O
the	O
Duflex	O
,	O
which	O
used	O
a	O
system	O
of	O
mirrors	O
to	O
provide	O
a	O
laterally	O
correct	O
,	O
upright	O
image	O
in	O
the	O
eye-level	O
viewfinder	O
.	O
</s>
<s>
The	O
Duflex	O
,	O
which	O
went	O
into	O
serial	O
production	O
in	O
1948	O
,	O
was	O
also	O
the	O
world	O
's	O
first	O
SLR	B-Algorithm
with	O
an	O
instant-return	O
(	O
a.k.a.	O
</s>
<s>
The	O
first	O
commercially	O
produced	O
SLR	B-Algorithm
that	O
employed	O
a	O
roof	O
pentaprism	O
was	O
the	O
Italian	O
Rectaflex	B-Algorithm
A.1000	O
,	O
shown	O
in	O
full	O
working	O
condition	O
on	O
Milan	O
fair	O
April	O
1948	O
and	O
produced	O
from	O
September	O
the	O
same	O
year	O
,	O
thus	O
being	O
on	O
the	O
market	O
one	O
year	O
before	O
the	O
east	O
German	O
Zeiss	O
Ikon	O
VEB	O
Contax	O
S	O
,	O
announced	O
on	O
May	O
20	O
,	O
1949	O
,	O
produced	O
from	O
September	O
.	O
</s>
<s>
The	O
Japanese	O
adopted	O
and	O
further	O
developed	O
the	O
SLR	B-Algorithm
.	O
</s>
<s>
In	O
1952	O
,	O
Asahi	B-Application
developed	O
the	O
Asahiflex	B-Algorithm
and	O
in	O
1954	O
,	O
the	O
Asahiflex	B-Algorithm
IIB	I-Algorithm
.	O
</s>
<s>
In	O
1957	O
,	O
the	O
Asahi	B-Algorithm
Pentax	I-Algorithm
combined	O
the	O
fixed	O
pentaprism	O
and	O
the	O
right-hand	O
thumb	O
wind	O
lever	O
.	O
</s>
<s>
Nikon	B-Algorithm
,	O
Canon	O
and	O
Yashica	O
introduced	O
their	O
first	O
SLRs	B-Algorithm
in	O
1959	O
(	O
the	O
F	B-Algorithm
,	O
Canonflex	B-Algorithm
,	O
and	O
Pentamatic	O
,	O
respectively	O
)	O
.	O
</s>
<s>
As	O
a	O
small	O
matter	O
of	O
history	O
,	O
the	O
first	O
35mm	O
camera	O
(	O
non-SLR	O
)	O
to	O
feature	O
through	O
the	O
lens	O
light	O
metering	O
may	O
have	O
been	O
Nikon	B-Algorithm
,	O
with	O
a	O
prototype	O
rangefinder	B-Algorithm
camera	I-Algorithm
,	O
the	O
SPX	O
.	O
</s>
<s>
According	O
to	O
the	O
website	O
below	O
,	O
the	O
camera	O
used	O
Nikon	B-Algorithm
'	O
S	O
 '	O
type	O
rangefinder	B-Algorithm
lenses	O
.	O
</s>
<s>
In	O
the	O
SLR	B-Algorithm
design	O
scheme	O
,	O
there	O
were	O
various	O
placements	O
made	O
for	O
the	O
metering	O
cells	O
,	O
all	O
of	O
which	O
used	O
CdS	O
(	O
Cadmium	O
sulfide	O
)	O
photocells	O
.	O
</s>
<s>
The	O
cells	O
were	O
either	O
located	O
in	O
the	O
pentaprism	O
housing	O
,	O
where	O
they	O
metered	O
light	O
transmitted	O
through	O
the	O
focusing	O
screen	O
;	O
underneath	O
the	O
reflex	O
mirror	O
glass	O
itself	O
,	O
which	O
was	O
Topcon	O
's	O
design	O
;	O
or	O
in	O
front	O
of	O
the	O
shutter	B-Algorithm
mechanism	O
,	O
which	O
was	O
the	O
design	O
used	O
by	O
Canon	O
with	O
their	O
Canon	B-Algorithm
Pellix	I-Algorithm
.	O
</s>
<s>
Pentax	B-Application
was	O
the	O
first	O
manufacturer	O
to	O
show	O
an	O
early	O
prototype	O
35mm	O
behind-the-lens	O
metering	O
SLR	B-Algorithm
camera	I-Algorithm
,	O
which	O
was	O
named	O
the	O
Pentax	B-Algorithm
Spotmatic	I-Algorithm
.	O
</s>
<s>
However	O
,	O
the	O
first	O
Through-the-lens	O
(	O
TTL	O
)	O
light	O
metering	O
SLR	B-Algorithm
on	O
the	O
market	O
was	O
the	O
1963	O
Topcon	B-Algorithm
RE	I-Algorithm
Super	I-Algorithm
,	O
which	O
had	O
the	O
CdS	O
metering	O
cell	O
placed	O
behind	O
the	O
reflex	O
mirror	O
.	O
</s>
<s>
The	O
mirror	O
had	O
narrow	O
slits	O
cut	O
into	O
the	O
surface	O
to	O
let	O
the	O
light	O
reach	O
the	O
cell	O
providing	O
average	B-Algorithm
metering	I-Algorithm
.	O
</s>
<s>
Late	O
in	O
the	O
following	O
year	O
,	O
a	O
production	O
model	O
of	O
the	O
Pentax	B-Algorithm
Spotmatic	I-Algorithm
was	O
shown	O
whose	O
CdS	O
light	O
meter	O
cells	O
were	O
on	O
the	O
pentaprism	O
,	O
reading	O
the	O
light	O
off	O
the	O
focusing	O
screen	O
providing	O
average	O
reading	O
,	O
yet	O
keeping	O
the	O
Spotmatic	B-Algorithm
name	O
,	O
but	O
now	O
written	O
in	O
one	O
word	O
.	O
</s>
<s>
Another	O
clever	O
design	O
appeared	O
in	O
1965	O
,	O
the	O
Canon	B-Algorithm
Pellix	I-Algorithm
employing	O
a	O
pellicle	B-Algorithm
mirror	I-Algorithm
that	O
is	O
semi-transparent	O
,	O
placing	O
the	O
meter	O
cell	O
on	O
an	O
arm	O
swinging	O
into	O
the	O
lightpass	O
behind	O
the	O
mirror	O
for	O
meter	O
reading	O
.	O
</s>
<s>
Both	O
of	O
these	O
cameras	O
used	O
M42	O
screw	O
thread	O
lenses	O
as	O
did	O
the	O
Pentax	B-Algorithm
Spotmatic	I-Algorithm
.	O
</s>
<s>
The	O
ST-701	O
was	O
the	O
first	O
SLR	B-Algorithm
to	O
use	O
a	O
silicon	O
cell	O
photodiode	O
,	O
which	O
was	O
more	O
sensitive	O
than	O
CdS	O
and	O
was	O
immune	O
to	O
the	O
memory	O
effect	O
that	O
the	O
CdS	O
cell	O
suffered	O
from	O
in	O
bright	O
sunlight	O
.	O
</s>
<s>
Gradually	O
,	O
other	O
35mm	O
SLR	B-Algorithm
camera	I-Algorithm
manufacturers	O
changed	O
their	O
behind-the-lens	O
meters	O
from	O
CdS	O
cells	O
to	O
Silicon	O
Diode	O
photocells	O
.	O
</s>
<s>
Nikon	B-Algorithm
and	O
Miranda	O
,	O
at	O
first	O
,	O
simply	O
upgraded	O
their	O
interchangeable	O
pentaprisms	O
to	O
include	O
behind-the-lens	O
metering	O
(	O
for	O
Nikon	B-Algorithm
F	I-Algorithm
,	O
and	O
Miranda	O
D	O
,	O
F	B-Algorithm
,	O
Fv	O
and	O
G	O
models	O
)	O
and	O
these	O
manufacturers	O
also	O
bought	O
out	O
other	O
camera	O
models	O
with	O
built-in	O
behind-the-lens	O
metering	O
capability	O
,	O
such	O
as	O
the	O
Nikkormat	O
FT	O
and	O
the	O
Miranda	O
Sensorex	O
(	O
which	O
used	O
an	O
external	O
coupling	O
diaphragm	O
)	O
.	O
</s>
<s>
Minolta	O
introduced	O
the	O
SRT-101	O
,	O
which	O
used	O
Minolta	O
's	O
proprietary	O
system	O
they	O
referred	O
to	O
as	O
"	O
CLC	O
"	O
,	O
which	O
was	O
an	O
acronym	O
for	O
"	O
contrast	O
light	O
compensation	O
"	O
,	O
which	O
metered	O
differently	O
from	O
an	O
average	B-Algorithm
metering	I-Algorithm
behind-the-lens	O
camera	O
.	O
</s>
<s>
Some	O
German	O
manufacturers	O
also	O
introduced	O
cameras	O
such	O
as	O
the	O
Zeiss	B-Algorithm
Ikon	I-Algorithm
Contarex	I-Algorithm
family	O
,	O
which	O
was	O
one	O
of	O
very	O
few	O
35mm	O
SLR	B-Algorithm
to	O
use	O
interchangeable	O
film	O
backs	O
.	O
</s>
<s>
Inexpensive	O
leaf-shutter	O
cameras	O
also	O
benefited	O
from	O
behind-the-lens	O
metering	O
as	O
,	O
Topcon	O
introduced	O
the	O
Auto	O
100	O
with	O
front-mount	O
interchangeable	O
lenses	O
designed	O
only	O
for	O
that	O
camera	O
,	O
and	O
one	O
of	O
the	O
Zeiss	O
Ikon	O
Contaflex	O
leaf	O
shutter	B-Algorithm
cameras	O
.	O
</s>
<s>
Within	O
months	O
,	O
manufacturers	O
decided	O
to	O
bring	O
out	O
models	O
that	O
provided	O
limited	O
area	O
metering	O
,	O
such	O
as	O
Nikon	B-Algorithm
's	O
Photomic	O
Tn	O
finder	O
,	O
which	O
concentrated	O
60%	O
of	O
the	O
CdS	O
cells	O
sensitivity	O
on	O
the	O
inner	O
circle	O
of	O
the	O
focusing	O
screen	O
and	O
30%	O
on	O
the	O
surrounding	O
area	O
.	O
</s>
<s>
Canon	O
used	O
spot	O
metering	O
in	O
the	O
unusual	O
Canon	B-Algorithm
Pellix	I-Algorithm
camera	O
,	O
which	O
also	O
had	O
a	O
stationary	O
mirror	O
system	O
that	O
allowed	O
approximately	O
70%	O
of	O
the	O
light	O
to	O
travel	O
to	O
the	O
film	O
plane	O
and	O
30%	O
to	O
the	O
photographer	O
's	O
eye	O
.	O
</s>
<s>
It	O
did	O
have	O
the	O
advantage	O
of	O
having	O
less	O
vibration	O
than	O
other	O
SLR	B-Algorithm
cameras	I-Algorithm
but	O
this	O
was	O
not	O
sufficient	O
to	O
attract	O
professionals	O
to	O
the	O
camera	O
in	O
numbers	O
.	O
</s>
<s>
While	O
auto-exposure	O
was	O
commonly	O
used	O
in	O
the	O
early	O
1960s	O
with	O
various	O
35mm	O
fixed	O
lens	O
rangefinder	B-Algorithm
cameras	I-Algorithm
such	O
as	O
the	O
Konica	O
Auto	O
'	O
S	O
 '	O
,	O
and	O
other	O
cameras	O
such	O
as	O
the	O
Polaroid	O
Land	O
cameras	O
whose	O
early	O
models	O
used	O
selenium	O
cell	O
meters	O
,	O
auto-exposure	O
for	O
interchangeable	O
lens	O
SLRs	B-Algorithm
was	O
a	O
feature	O
that	O
was	O
largely	O
absent	O
,	O
except	O
for	O
a	O
few	O
early	O
leaf-shutter	O
SLRs	B-Algorithm
such	O
as	O
the	O
Kowa	O
SE-R	O
and	O
Topcon	O
Auto	O
100	O
.	O
</s>
<s>
The	O
types	O
of	O
automation	O
found	O
in	O
some	O
of	O
these	O
cameras	O
consisted	O
of	O
the	O
simple	O
programmed	O
shutter	B-Algorithm
,	O
whereby	O
the	O
camera	O
's	O
metering	O
system	O
would	O
select	O
a	O
mechanically	O
set	O
series	O
of	O
apertures	B-General_Concept
with	O
shutter	B-Algorithm
speeds	O
,	O
one	O
setting	O
of	O
which	O
would	O
be	O
sufficient	O
for	O
the	O
correct	O
exposure	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
the	O
above-mentioned	O
Kowa	O
and	O
Topcon	O
,	O
automation	O
was	O
semi-automatic	O
,	O
where	O
the	O
camera	O
's	O
CDs	O
meter	O
would	O
select	O
the	O
correct	O
aperture	B-General_Concept
only	O
.	O
</s>
<s>
Autoexposure	O
,	O
technically	O
known	O
as	O
semi-automatic	O
exposure	O
,	O
where	O
the	O
camera	O
's	O
metering	O
system	O
chooses	O
either	O
the	O
shutter	B-Algorithm
speed	O
or	O
the	O
aperture	B-General_Concept
,	O
was	O
finally	O
introduced	O
by	O
the	O
Savoyflex	O
and	O
popularized	O
by	O
Konishiroku	O
in	O
the	O
1965	O
Konica	O
Auto-Reflex	O
.	O
</s>
<s>
This	O
camera	O
was	O
of	O
the	O
'	O
shutter-priority	B-Algorithm
'	O
type	O
automation	O
,	O
which	O
meant	O
that	O
the	O
camera	O
selected	O
the	O
correct	O
aperture	B-General_Concept
automatically	O
.	O
</s>
<s>
Other	O
SLRs	B-Algorithm
soon	O
followed	O
,	O
but	O
because	O
of	O
limitations	O
with	O
their	O
lens	O
mounts	O
,	O
the	O
manufacturers	O
of	O
these	O
cameras	O
had	O
to	O
choose	O
'	O
aperture-priority	B-Algorithm
'	O
automation	O
,	O
where	O
the	O
camera	O
's	O
metering	O
system	O
selects	O
the	O
correct	O
shutter	B-Algorithm
speed	O
.	O
</s>
<s>
As	O
one	O
example	O
,	O
Pentax	B-Application
introduced	O
the	O
Electro	O
Spotmatic	B-Algorithm
,	O
which	O
was	O
able	O
to	O
use	O
the	O
then	O
considerable	O
bulk	O
of	O
42mm	O
screw-mount	O
lenses	O
produced	O
by	O
various	O
manufacturers	O
.	O
</s>
<s>
Canon	O
,	O
which	O
produced	O
the	O
FD	B-Algorithm
lens	I-Algorithm
mount	I-Algorithm
(	O
known	O
as	O
the	O
breech-mount	O
;	O
a	O
unique	O
lens	O
mounting	O
system	O
that	O
combines	O
the	O
advantages	O
of	O
screw-mount	O
and	O
bayonet-mount	O
)	O
introduced	O
their	O
shutter	B-Algorithm
priority	I-Algorithm
35mm	O
SLR	B-Algorithm
,	O
the	O
Canon	O
EF	O
in	O
1976	O
or	O
so	O
.	O
</s>
<s>
This	O
camera	O
's	O
build	O
quality	O
was	O
almost	O
the	O
equal	O
of	O
their	O
flagship	O
camera	O
,	O
the	O
Canon	O
F1	O
,	O
and	O
featured	O
a	O
copal-square	O
vertically	O
travelling	O
focal	O
plane	O
shutter	B-Algorithm
that	O
could	O
synchronize	O
electronic	O
flash	O
at	O
shutter	B-Algorithm
speeds	O
up	O
to	O
and	O
including	O
1/125	O
of	O
a	O
second	O
,	O
thus	O
making	O
this	O
a	O
good	O
second-body	O
camera	O
for	O
the	O
professional	O
photographer	O
.	O
</s>
<s>
Nikon	B-Algorithm
at	O
first	O
produced	O
an	O
aperture-priority	B-Algorithm
camera	O
,	O
but	O
later	O
made	O
subtle	O
changes	O
on	O
the	O
inside	O
of	O
their	O
bayonet	O
mount	O
,	O
which	O
allowed	O
for	O
shutter-priority	B-Algorithm
automation	O
without	O
obsoleting	O
the	O
photographers	O
lenses	O
.	O
</s>
<s>
This	O
SLR	B-Algorithm
had	O
a	O
'	O
P	O
 '	O
mode	O
on	O
the	O
shutter	B-Algorithm
speed	O
dial	O
,	O
and	O
a	O
lock	O
on	O
the	O
aperture	B-General_Concept
ring	O
to	O
allow	O
the	O
lens	O
to	O
be	O
put	O
on	O
'	O
Auto	O
 '	O
mode	O
.	O
</s>
<s>
Other	O
manufacturers	O
soon	O
followed	O
with	O
Nikon	B-Algorithm
introducing	O
the	O
FA	O
,	O
Minolta	O
introducing	O
the	O
X-700	O
in	O
1981	O
,	O
and	O
Pentax	B-Application
introducing	O
the	O
Super	O
Program	O
.	O
</s>
<s>
Olympus	O
,	O
however	O
,	O
continued	O
with	O
'	O
aperture-priority	B-Algorithm
'	O
automation	O
in	O
their	O
OM	O
system	O
line	O
.	O
</s>
<s>
The	O
first	O
autofocus	O
35mm	O
SLR	B-Algorithm
was	O
the	O
Pentax	B-Algorithm
ME-F	I-Algorithm
released	O
in	O
1981	O
.	O
</s>
<s>
The	O
Minolta	B-Algorithm
Maxxum	I-Algorithm
7000	I-Algorithm
,	O
released	O
in	O
1985	O
,	O
was	O
the	O
first	O
35mm	O
SLR	B-Algorithm
with	O
integrated	O
autofocus	O
and	O
motorized	O
film-advance	O
winder	O
,	O
which	O
became	O
the	O
standard	O
configuration	O
for	O
SLR	B-Algorithm
cameras	I-Algorithm
from	O
then	O
on	O
.	O
</s>
<s>
Other	O
manufacturers	O
chose	O
to	O
adapt	O
their	O
existing	O
lens	O
systems	O
for	O
autofocus	O
capability	O
,	O
as	O
was	O
the	O
case	O
with	O
Nikon	B-Algorithm
and	O
Pentax	B-Application
.	O
</s>
<s>
For	O
example	O
,	O
almost	O
all	O
Nikon	B-Algorithm
lenses	O
from	O
the	O
1960s	O
and	O
later	O
still	O
function	O
on	O
the	O
current	O
Nikon	B-Algorithm
bodies	O
,	O
only	O
lacking	O
autofocus	O
.	O
</s>
<s>
Still	O
some	O
manufacturers	O
,	O
notably	O
Leica	O
with	O
its	O
R-system	B-Algorithm
lenses	O
,	O
and	O
Contax	O
with	O
its	O
Zeiss	O
lenses	O
,	O
decided	O
to	O
keep	O
their	O
lens	O
mounts	O
non-autofocus	O
.	O
</s>
<s>
From	O
the	O
late	O
1980s	O
competition	O
and	O
technical	O
innovations	O
made	O
35mm	O
camera	O
systems	O
more	O
versatile	O
and	O
sophisticated	O
by	O
adding	O
more	O
advanced	O
light	O
metering	O
capabilities	O
such	O
as	O
spot-metering	O
;	O
limited	O
area	O
metering	O
such	O
as	O
used	O
by	O
Canon	O
with	O
the	O
F1	O
series	O
;	O
matrix	B-Algorithm
metering	I-Algorithm
as	O
used	O
by	O
Nikon	B-Algorithm
,	O
exposure	O
communication	O
with	O
dedicated	O
electronic	O
flash	O
units	O
.	O
</s>
<s>
The	O
user	O
interface	O
also	O
changed	O
on	O
many	O
cameras	O
,	O
replacing	O
meter	O
needle	O
displays	O
that	O
were	O
galvanometer-based	O
and	O
thereby	O
fragile	O
,	O
with	O
light-emitting	O
diodes	O
(	O
LEDs	O
)	O
and	O
then	O
with	O
more	O
comprehensive	O
liquid	B-Device
crystal	I-Device
displays	I-Device
(	O
LCDs	B-Device
)	O
both	O
in	O
the	O
SLR	B-Algorithm
viewfinder	O
and	O
externally	O
on	O
the	O
cameras	O
 '	O
top	O
plate	O
using	O
an	O
LCD	B-Device
screen	I-Device
.	O
</s>
<s>
Wheels	O
and	O
buttons	O
replaced	O
the	O
shutter	B-Algorithm
dial	O
on	O
the	O
camera	O
and	O
the	O
aperture	B-General_Concept
ring	O
on	O
the	O
lens	O
on	O
many	O
models	O
,	O
although	O
some	O
photographers	O
still	O
prefer	O
shutter	B-Algorithm
dials	O
and	O
aperture	B-General_Concept
rings	O
.	O
</s>
<s>
Canon	O
,	O
Nikon	B-Algorithm
and	O
Pentax	B-Application
have	O
all	O
developed	O
digital	B-Device
SLR	I-Device
cameras	I-Device
(	O
DSLRs	B-Device
)	O
using	O
the	O
same	O
lens	O
mounts	O
as	O
on	O
their	O
respective	O
film	O
SLR	B-Algorithm
cameras	I-Algorithm
.	O
</s>
<s>
Konica	O
Minolta	O
did	O
the	O
same	O
,	O
and	O
after	O
having	O
bought	O
Konica	O
Minolta	O
's	O
camera	O
division	O
in	O
2006	O
Sony	O
continue	O
using	O
the	O
Minolta	O
AF	O
lens	O
mount	O
in	O
their	O
DSLRs	B-Device
,	O
including	O
cameras	O
built	O
around	O
a	B-Device
semi-transparent	I-Device
fixed	I-Device
mirror	I-Device
.	O
</s>
<s>
Samsung	O
builds	O
DSLRs	B-Device
based	O
on	O
the	O
Pentax	B-Application
lens	O
mount	O
.	O
</s>
<s>
Olympus	O
,	O
on	O
the	O
other	O
hand	O
,	O
chose	O
to	O
create	O
a	O
new	O
digital-only	O
Four	B-Architecture
Thirds	I-Architecture
System	I-Architecture
SLR	B-Algorithm
standard	O
,	O
adopted	O
later	O
by	O
Panasonic	O
and	O
Leica	O
.	O
</s>
<s>
Contax	O
came	O
out	O
with	O
a	O
DSLR	B-Device
model	O
,	O
the	O
Contax	B-Algorithm
N-Digital	I-Algorithm
.	O
</s>
<s>
The	O
Contax	B-Algorithm
N-digital	I-Algorithm
was	O
the	O
last	O
Contax	O
to	O
use	O
that	O
maker	O
's	O
lens	O
system	O
,	O
and	O
the	O
camera	O
,	O
while	O
having	O
impressive	O
features	O
such	O
as	O
a	O
full-frame	O
sensor	B-Algorithm
,	O
was	O
expensive	O
and	O
lacked	O
sufficient	O
write-speed	O
to	O
the	O
memory	O
card	O
for	O
it	O
to	O
be	O
seriously	O
considered	O
by	O
some	O
professional	O
photographers	O
.	O
</s>
<s>
The	O
digital	B-Device
single-lens	I-Device
reflex	I-Device
camera	I-Device
have	O
largely	O
replaced	O
film	O
SLRs	B-Algorithm
design	O
in	O
convenience	O
,	O
sales	O
and	O
popularity	O
at	O
the	O
start	O
of	O
21st	O
century	O
.	O
</s>
<s>
A	O
cross-section	O
(	O
or	O
'	O
side-view	O
'	O
)	O
of	O
the	O
optical	O
components	O
of	O
a	O
typical	O
SLR	B-Algorithm
camera	I-Algorithm
shows	O
how	O
the	O
light	O
passes	O
through	O
the	O
lens	O
assembly	O
(	O
1	O
)	O
,	O
is	O
reflected	O
by	O
the	O
mirror	O
(	O
2	O
)	O
placed	O
at	O
a	O
45-degree	O
angle	O
,	O
and	O
is	O
projected	O
on	O
the	O
matte	O
focusing	O
screen	O
(	O
5	O
)	O
.	O
</s>
<s>
When	O
an	O
image	O
is	O
taken	O
,	O
the	O
mirror	O
moves	O
upwards	O
from	O
its	O
resting	O
position	O
in	O
the	O
direction	O
of	O
the	O
arrow	O
,	O
the	O
focal	O
plane	O
shutter	B-Algorithm
(	O
3	O
)	O
opens	O
,	O
and	O
the	O
image	O
is	O
projected	O
onto	O
the	O
film	O
or	O
sensor	B-Algorithm
(	O
4	O
)	O
in	O
exactly	O
the	O
same	O
manner	O
as	O
on	O
the	O
focusing	O
screen	O
.	O
</s>
<s>
This	O
feature	O
distinguishes	O
SLRs	B-Algorithm
from	O
other	O
cameras	O
as	O
the	O
photographer	O
sees	O
the	O
image	O
composed	O
exactly	O
as	O
it	O
will	O
be	O
captured	O
on	O
the	O
film	O
or	O
sensor	B-Algorithm
(	O
see	O
Advantages	O
below	O
)	O
.	O
</s>
<s>
Most	O
35mm	O
SLRs	B-Algorithm
use	O
a	O
roof	O
pentaprism	O
or	O
penta-mirror	O
to	O
direct	O
the	O
light	O
to	O
the	O
eyepiece	O
,	O
first	O
used	O
on	O
the	O
1948	O
Duflex	O
constructed	O
by	O
Jenő	O
Dulovits	O
and	O
patented	O
August	O
1943	O
(	O
Hungary	O
)	O
.	O
</s>
<s>
With	O
this	O
camera	O
also	O
appeared	O
the	O
first	O
Instant-return	B-Algorithm
mirror	I-Algorithm
.	O
</s>
<s>
The	O
first	O
Japanese	O
pentaprism	O
SLR	B-Algorithm
was	O
the	O
1955	O
Miranda	B-Algorithm
T	I-Algorithm
,	O
followed	O
by	O
the	O
Asahi	B-Algorithm
Pentax	I-Algorithm
,	O
Minolta	O
SR-2	O
,	O
Zunow	O
,	O
Nikon	B-Algorithm
F	I-Algorithm
and	O
the	O
Yashica	O
Pentamatic	O
.	O
</s>
<s>
Some	O
SLRs	B-Algorithm
offered	O
removable	O
pentaprisms	O
with	O
optional	O
viewfinder	O
capabilities	O
,	O
such	O
as	O
the	O
waist-level	B-Algorithm
finder	I-Algorithm
,	O
the	O
interchangeable	O
sports	O
finders	O
used	O
on	O
the	O
Canon	O
F1	O
and	O
F1n	O
;	O
the	O
Nikon	B-Algorithm
F	I-Algorithm
,	O
F2	B-Algorithm
,	O
F3	B-Algorithm
,	O
F4	O
and	O
F5	O
;	O
and	O
the	O
Pentax	B-Application
LX	O
.	O
</s>
<s>
Another	O
prism	O
design	O
was	O
the	O
porro	O
prism	O
system	O
used	O
in	O
the	O
Olympus	B-Algorithm
Pen	I-Algorithm
F	I-Algorithm
,	O
the	O
Pen	O
FT	O
,	O
the	O
Pen	O
FV	O
half-frame	O
35mm	O
SLR	B-Algorithm
cameras	I-Algorithm
.	O
</s>
<s>
This	O
was	O
later	O
used	O
on	O
the	O
Olympus	B-Algorithm
EVOLT	I-Algorithm
E-3x0	I-Algorithm
series	O
,	O
the	O
Leica	O
Digilux	O
3	O
and	O
the	O
Panasonic	B-Device
DMC-L1	I-Device
.	O
</s>
<s>
A	O
right-angle	O
finder	O
is	O
available	O
that	O
slips	O
onto	O
the	O
eyepiece	O
of	O
most	O
SLRs	B-Algorithm
and	O
D-SLRs	B-Device
and	O
allows	O
viewing	O
through	O
a	O
waist-level	O
viewfinder	O
.	O
</s>
<s>
Almost	O
all	O
contemporary	O
SLRs	B-Algorithm
use	O
a	O
focal-plane	O
shutter	B-Algorithm
located	O
in	O
front	O
of	O
the	O
film	O
plane	O
,	O
which	O
prevents	O
the	O
light	O
from	O
reaching	O
the	O
film	O
even	O
if	O
the	O
lens	O
is	O
removed	O
,	O
except	O
when	O
the	O
shutter	B-Algorithm
is	O
actually	O
released	O
during	O
the	O
exposure	O
.	O
</s>
<s>
Early	O
focal-plane	O
shutters	O
designed	O
from	O
the	O
1930s	O
onwards	O
usually	O
consisted	O
of	O
two	O
curtains	O
that	O
travelled	O
horizontally	O
across	O
the	O
film	O
gate	O
:	O
an	O
opening	O
shutter	B-Algorithm
curtain	O
followed	O
by	O
a	O
closing	O
shutter	B-Algorithm
curtain	O
.	O
</s>
<s>
During	O
fast	O
shutter	B-Algorithm
speeds	O
,	O
the	O
focal-plane	O
shutter	B-Algorithm
would	O
form	O
a	O
'	O
slit	O
 '	O
whereby	O
the	O
second	O
shutter	B-Algorithm
curtain	O
was	O
closely	O
following	O
the	O
first	O
opening	O
shutter	B-Algorithm
curtain	O
to	O
produce	O
a	O
narrow	O
,	O
vertical	O
opening	O
,	O
with	O
the	O
shutter	B-Algorithm
slit	O
moving	O
horizontally	O
.	O
</s>
<s>
The	O
slit	O
would	O
get	O
narrower	O
as	O
shutter	B-Algorithm
speeds	O
were	O
increased	O
.	O
</s>
<s>
Nippon	O
Kōgaku	O
(	O
now	O
Nikon	B-Algorithm
Corporation	O
)	O
,	O
for	O
example	O
,	O
used	O
titanium	O
foil	O
shutters	O
for	O
several	O
of	O
their	O
flagship	O
SLR	B-Algorithm
cameras	I-Algorithm
,	O
including	O
the	O
Nikon	B-Algorithm
F	I-Algorithm
,	O
F2	B-Algorithm
,	O
and	O
F3	B-Algorithm
.	O
</s>
<s>
Other	O
focal-plane	O
shutter	B-Algorithm
designs	O
,	O
such	O
as	O
the	O
Copal	O
Square	O
,	O
travelled	O
vertically	O
—	O
the	O
shorter	O
travelling	O
distance	O
of	O
24	O
millimetres	O
(	O
as	O
opposed	O
to	O
36mm	O
horizontally	O
)	O
meant	O
that	O
minimum	O
exposure	O
and	O
flash	O
synchronisation	O
times	O
could	O
be	O
reduced	O
.	O
</s>
<s>
They	O
differ	O
,	O
though	O
,	O
in	O
usually	O
being	O
formed	O
of	O
several	O
slats	O
or	O
blades	O
,	O
rather	O
than	O
single	O
curtains	O
as	O
with	O
horizontal	O
designs	O
,	O
as	O
there	O
is	O
rarely	O
enough	O
room	O
above	O
and	O
below	O
the	O
frame	O
for	O
a	O
one-piece	O
shutter	B-Algorithm
.	O
</s>
<s>
Nikon	B-Algorithm
used	O
Copal-made	O
vertical	O
plane	O
shutters	O
in	O
their	O
Nikomat/Nikkormat	O
-range	O
,	O
enabling	O
x-sync	O
speeds	O
from	O
to	O
while	O
the	O
only	O
choice	O
for	O
focal	O
plane	O
shutters	O
at	O
that	O
time	O
was	O
.	O
</s>
<s>
Later	O
,	O
Nikon	B-Algorithm
again	O
pioneered	O
the	O
use	O
of	O
titanium	O
for	O
vertical	O
shutters	O
,	O
using	O
a	O
special	O
honeycomb	O
pattern	O
on	O
the	O
blades	O
to	O
reduce	O
their	O
weight	O
and	O
achieve	O
world-record	O
speeds	O
in	O
1982	O
of	O
second	O
for	O
non-sync	O
shooting	O
,	O
and	O
with	O
x-sync	O
.	O
</s>
<s>
One	O
unusual	O
design	O
,	O
the	O
Olympus	B-Algorithm
Pen	I-Algorithm
half-frame	O
35mm	O
SLR	B-Algorithm
system	O
,	O
manufactured	O
by	O
Olympus	O
in	O
Japan	O
,	O
used	O
a	O
rotary	O
focal-plane	O
shutter	B-Algorithm
mechanism	O
that	O
was	O
extremely	O
simple	O
and	O
elegant	O
in	O
design	O
.	O
</s>
<s>
Another	O
35mm	O
camera	O
system	O
that	O
used	O
a	O
rotary	O
shutter	B-Algorithm
,	O
was	O
the	O
Robot	O
Royal	O
cameras	O
,	O
most	O
of	O
which	O
were	O
rangefinder	B-Algorithm
35mm	O
cameras	O
.	O
</s>
<s>
The	O
Mercury	O
II	O
,	O
produced	O
in	O
1946	O
,	O
also	O
used	O
a	O
rotary	O
shutter	B-Algorithm
.	O
</s>
<s>
Another	O
shutter	B-Algorithm
system	O
is	O
the	O
leaf	O
shutter	B-Algorithm
,	O
whereby	O
the	O
shutter	B-Algorithm
is	O
constructed	O
of	O
diaphragm-like	O
blades	O
and	O
can	O
be	O
situated	O
either	O
between	O
the	O
lens	O
or	O
behind	O
the	O
lens	O
.	O
</s>
<s>
If	O
the	O
shutter	B-Algorithm
is	O
part	O
of	O
a	O
lens	O
assembly	O
some	O
other	O
mechanism	O
is	O
required	O
to	O
ensure	O
that	O
no	O
light	O
reaches	O
the	O
film	O
between	O
exposures	O
.	O
</s>
<s>
An	O
example	O
of	O
a	O
behind-the-lens	O
leaf	O
shutter	B-Algorithm
is	O
found	O
in	O
the	O
35mm	O
SLRs	B-Algorithm
produced	O
by	O
Kodak	O
,	O
with	O
their	O
Retina	O
Reflex	O
camera	O
line	O
;	O
Topcon	O
,	O
with	O
their	O
Auto	O
100	O
;	O
and	O
Kowa	O
with	O
their	O
SE-R	O
and	O
SET-R	O
reflexes	O
.	O
</s>
<s>
A	O
primary	O
example	O
of	O
a	O
medium-format	O
SLR	B-Algorithm
with	O
a	O
between-the-lens	O
leaf	O
shutter	B-Algorithm
system	O
would	O
be	O
Hasselblad	B-Algorithm
,	O
with	O
their	O
500C	O
,	O
500cm	B-Algorithm
,	O
500	O
EL-M	O
(	O
a	O
motorized	O
Hasselblad	B-Algorithm
)	O
and	O
other	O
models	O
(	O
producing	O
a	O
6cm	O
square	O
negative	O
)	O
.	O
</s>
<s>
Hasselblads	B-Algorithm
use	O
an	O
auxiliary	O
shutter	B-Algorithm
blind	O
situated	O
behind	O
the	O
lens	O
mount	O
and	O
the	O
mirror	O
system	O
to	O
prevent	O
the	O
fogging	O
of	O
film	O
.	O
</s>
<s>
Other	O
medium-format	O
SLRs	B-Algorithm
also	O
using	O
leaf	O
shutters	O
include	O
the	O
now	O
discontinued	O
Zenza-Bronica	O
camera	O
system	O
lines	O
such	O
as	O
the	O
Bronica	O
ETRs	O
,	O
the	O
ETRs'i	O
(	O
both	O
producing	O
a	O
6×	O
4.5cm	O
.	O
</s>
<s>
image	O
)	O
,	O
the	O
SQ	O
and	O
the	O
SQ-AI	O
(	O
producing	O
a	O
6×6cm	O
image	O
like	O
the	O
Hasselblad	B-Algorithm
)	O
,	O
and	O
the	O
Zenza-Bronica	O
G	O
system	O
(	O
6×7cm	O
)	O
.	O
</s>
<s>
Certain	O
Mamiya	O
medium-format	O
SLRs	B-Algorithm
,	O
discontinued	O
camera	O
systems	O
such	O
as	O
the	O
Kowa	O
6	O
and	O
a	O
few	O
other	O
camera	O
models	O
also	O
used	O
between-the-lens	O
leaf	O
shutters	O
in	O
their	O
lens	O
systems	O
.	O
</s>
<s>
Thus	O
,	O
any	O
time	O
a	O
photographer	O
purchased	O
one	O
of	O
these	O
lenses	O
,	O
that	O
lens	O
included	O
a	O
leaf	O
shutter	B-Algorithm
in	O
its	O
lens	O
mount	O
.	O
</s>
<s>
Because	O
leaf	O
shutters	O
synchronized	O
electronic	O
flash	O
at	O
all	O
shutter	B-Algorithm
speeds	O
especially	O
at	O
fast	O
shutter	B-Algorithm
speeds	O
of	O
of	O
a	O
second	O
or	O
faster	O
,	O
cameras	O
using	O
leaf	O
shutters	O
were	O
more	O
desirable	O
to	O
studio	O
photographers	O
who	O
used	O
sophisticated	O
studio	O
electronic	O
flash	O
systems	O
.	O
</s>
<s>
Some	O
manufacturers	O
of	O
medium-format	O
120	O
film	O
SLR	B-Algorithm
cameras	I-Algorithm
also	O
made	O
leaf-shutter	O
lenses	O
for	O
their	O
focal-plane-shutter	O
models	O
.	O
</s>
<s>
Rollei	O
made	O
at	O
least	O
two	O
such	O
lenses	O
for	O
their	O
Rolleiflex	O
SL-66	O
medium	O
format	O
which	O
was	O
a	O
focal-plane	O
shutter	B-Algorithm
SLR	B-Algorithm
.	O
</s>
<s>
Rollei	O
later	O
switched	O
to	O
a	O
camera	O
system	O
of	O
leaf-shutter	O
design	O
(	O
e.g.	O
,	O
the	O
6006	O
and	O
6008	O
reflexes	O
)	O
and	O
their	O
current	O
medium-format	O
SLRs	B-Algorithm
are	O
now	O
all	O
of	O
the	O
between-the-lens	O
shutter	B-Algorithm
design	O
.	O
</s>
<s>
Since	O
the	O
technology	O
became	O
widespread	O
in	O
the	O
1970s	O
,	O
SLRs	B-Algorithm
have	O
become	O
the	O
main	O
photographic	O
instrument	O
used	O
by	O
dedicated	O
amateur	O
photographers	O
and	O
professionals	O
.	O
</s>
<s>
Some	O
photographers	O
of	O
static	O
subjects	O
(	O
such	O
as	O
architecture	O
,	O
landscape	O
,	O
and	O
some	O
commercial	O
subjects	O
)	O
,	O
however	O
,	O
prefer	O
view	B-Algorithm
cameras	I-Algorithm
because	O
of	O
the	O
capability	O
to	O
control	O
perspective	O
.	O
</s>
<s>
Early	O
SLRs	B-Algorithm
were	O
built	O
for	O
large	O
format	O
photography	O
,	O
but	O
this	O
film	O
format	O
has	O
largely	O
lost	O
favor	O
among	O
professional	O
photographers	O
.	O
</s>
<s>
SLR	B-Algorithm
film-based	O
cameras	O
have	O
been	O
produced	O
for	O
most	O
film	O
formats	O
as	O
well	O
as	O
for	O
digital	O
formats	O
.	O
</s>
<s>
These	O
film-based	O
SLRs	B-Algorithm
use	O
the	O
35	O
mm	O
format	O
as	O
,	O
this	O
film	O
format	O
offers	O
a	O
variety	O
of	O
emulsions	O
and	O
film	O
sensitivity	O
speeds	O
,	O
usable	O
image	O
quality	O
and	O
a	O
good	O
market	O
cost	O
.	O
</s>
<s>
Medium	O
format	O
SLRs	B-Algorithm
provide	O
a	O
higher-quality	O
image	O
with	O
a	O
negative	O
that	O
can	O
be	O
more	O
easily	O
retouched	O
than	O
the	O
smaller	O
35mm	O
negative	O
,	O
when	O
this	O
capability	O
is	O
required	O
.	O
</s>
<s>
A	O
small	O
number	O
of	O
SLRs	B-Algorithm
were	O
built	O
for	O
APS	O
such	O
as	O
the	O
Canon	O
IX	O
series	O
and	O
the	O
Nikon	B-Algorithm
Pronea	O
cameras	O
.	O
</s>
<s>
SLRs	B-Algorithm
were	O
also	O
introduced	O
for	O
film	O
formats	O
as	O
small	O
as	O
Kodak	O
's	O
110	O
,	O
such	O
as	O
the	O
Pentax	B-Algorithm
Auto	I-Algorithm
110	I-Algorithm
,	O
which	O
had	O
interchangeable	O
lenses	O
.	O
</s>
<s>
The	O
Narciss	B-Algorithm
camera	I-Algorithm
is	O
an	O
all-metal	O
16mm	O
subminiature	O
single	B-Algorithm
lens	I-Algorithm
reflex	I-Algorithm
camera	I-Algorithm
made	O
by	O
Russian	O
optic	O
firm	O
Krasnogorsky	O
Mekhanichesky	O
Zavod	O
(	O
KMZ	O
)	O
Narciss	O
(	O
Soviet	O
Union	O
;	O
Нарцисс	O
)	O
between	O
1961	O
and	O
1965	O
.	O
</s>
<s>
Other	O
features	O
found	O
on	O
many	O
SLR	B-Algorithm
cameras	I-Algorithm
include	O
through-the-lens	O
(	O
TTL	O
)	O
metering	O
and	O
sophisticated	O
flash	O
control	O
referred	O
to	O
as	O
"	O
dedicated	O
electronic	O
flash	O
"	O
.	O
</s>
<s>
In	O
a	O
dedicated	O
system	O
,	O
once	O
the	O
dedicated	O
electronic	O
flash	O
is	O
inserted	O
into	O
the	O
camera	O
's	O
hot	B-Algorithm
shoe	I-Algorithm
and	O
turned	O
on	O
,	O
there	O
is	O
then	O
communication	O
between	O
camera	O
and	O
flash	O
.	O
</s>
<s>
The	O
camera	O
's	O
synchronization	O
speed	O
is	O
set	O
,	O
along	O
with	O
the	O
aperture	B-General_Concept
.	O
</s>
<s>
While	O
these	O
capabilities	O
are	O
not	O
unique	O
to	O
the	O
SLR	B-Algorithm
,	O
manufacturers	O
included	O
them	O
early	O
on	O
in	O
the	O
top	O
models	O
,	O
whereas	O
the	O
best	O
rangefinder	B-Algorithm
cameras	I-Algorithm
adopted	O
such	O
features	O
later	O
.	O
</s>
<s>
Many	O
of	O
the	O
advantages	O
of	O
SLR	B-Algorithm
cameras	I-Algorithm
derive	O
from	O
viewing	O
and	O
focusing	O
the	O
image	O
through	O
the	O
attached	O
lens	O
.	O
</s>
<s>
SLR	B-Algorithm
cameras	I-Algorithm
provide	O
photographers	O
with	O
precision	O
;	O
they	O
provide	O
a	O
viewing	O
image	O
that	O
will	O
be	O
exposed	O
onto	O
the	O
negative	O
exactly	O
as	O
it	O
is	O
seen	O
through	O
the	O
lens	O
.	O
</s>
<s>
There	O
is	O
no	O
parallax	B-Device
error	O
,	O
and	O
exact	O
focus	O
can	O
be	O
confirmed	O
by	O
eye	O
—	O
especially	O
in	O
macro	O
photography	O
and	O
when	O
photographing	O
using	O
long	O
focus	O
lenses	O
.	O
</s>
<s>
The	O
depth	O
of	O
field	O
may	O
be	O
seen	O
by	O
stopping	O
down	O
to	O
the	O
attached	O
lens	O
aperture	B-General_Concept
,	O
which	O
is	O
possible	O
on	O
most	O
SLR	B-Algorithm
cameras	I-Algorithm
except	O
for	O
the	O
least	O
expensive	O
models	O
.	O
</s>
<s>
Because	O
of	O
the	O
SLR	B-Algorithm
's	O
versatility	O
,	O
most	O
manufacturers	O
have	O
a	O
vast	O
range	O
of	O
lenses	O
and	O
accessories	O
available	O
for	O
them	O
.	O
</s>
<s>
Compared	O
to	O
most	O
fixed-lens	O
compact	B-Algorithm
cameras	I-Algorithm
,	O
the	O
most	O
commonly	O
used	O
and	O
inexpensive	O
SLR	B-Algorithm
lenses	O
offer	O
a	O
wider	O
aperture	B-General_Concept
range	O
and	O
larger	O
maximum	O
aperture	B-General_Concept
(	O
typically	O
to	O
for	O
a	O
50mm	O
lens	O
)	O
.	O
</s>
<s>
"	O
Fast	O
"	O
lenses	O
are	O
commonly	O
used	O
in	O
theater	O
photography	O
,	O
portrait	O
photography	O
,	O
surveillance	O
photography	O
,	O
and	O
all	O
other	O
photography	O
requiring	O
a	O
large	O
maximum	O
aperture	B-General_Concept
.	O
</s>
<s>
This	O
provides	O
the	O
photographer	O
with	O
considerably	O
more	O
control	O
(	O
i.e.	O
,	O
how	O
the	O
image	O
is	O
viewed	O
and	O
framed	O
)	O
than	O
would	O
be	O
the	O
case	O
with	O
a	O
view	B-Algorithm
camera	I-Algorithm
.	O
</s>
<s>
In	O
addition	O
,	O
some	O
SLR	B-Algorithm
lenses	O
are	O
manufactured	O
with	O
extremely	O
long	O
focal	O
lengths	O
,	O
allowing	O
a	O
photographer	O
to	O
be	O
a	O
considerable	O
distance	O
away	O
from	O
the	O
subject	O
and	O
yet	O
still	O
expose	O
a	O
sharp	O
,	O
focused	O
image	O
.	O
</s>
<s>
Practically	O
all	O
SLR	B-Algorithm
and	O
DSLR	B-Device
camera	I-Device
bodies	O
can	O
also	O
be	O
attached	O
to	O
telescopes	O
and	O
microscopes	O
via	O
an	O
adapter	O
tube	O
to	O
further	O
enhance	O
their	O
imaging	O
capabilities	O
.	O
</s>
<s>
In	O
most	O
cases	O
,	O
single-lens	B-Algorithm
reflex	I-Algorithm
cameras	I-Algorithm
cannot	O
be	O
made	O
as	O
small	O
or	O
as	O
light	O
as	O
other	O
camera	O
designs	O
—	O
such	O
as	O
rangefinder	B-Algorithm
cameras	I-Algorithm
,	O
autofocus	O
compact	B-Algorithm
cameras	I-Algorithm
and	O
digital	O
cameras	O
with	O
electronic	B-Algorithm
viewfinders	I-Algorithm
(	O
EVF	O
)	O
—	O
owing	O
to	O
the	O
mirror	O
box	O
and	O
pentaprism/pentamirror	O
.	O
</s>
<s>
The	O
mirror	O
box	O
also	O
prevents	O
lenses	O
with	O
deeply	O
recessed	O
rear	O
elements	O
from	O
being	O
mounted	O
close	O
to	O
the	O
film	O
or	O
sensor	B-Algorithm
unless	O
the	O
camera	O
has	O
a	O
mirror	O
lockup	O
feature	O
;	O
this	O
means	O
that	O
simple	O
designs	O
for	O
wide	O
angle	O
lenses	O
cannot	O
be	O
used	O
.	O
</s>
<s>
The	O
SLR	B-Algorithm
mirror	O
'	O
blacks-out	O
'	O
the	O
viewfinder	O
image	O
during	O
the	O
exposure	O
.	O
</s>
<s>
Partially	O
reflective	O
(	O
pellicle	B-Algorithm
)	O
fixed	O
mirrors	O
avoid	O
these	O
problems	O
and	O
have	O
been	O
used	O
in	O
a	O
very	O
few	O
designs	O
including	O
the	O
Canon	B-Algorithm
Pellix	I-Algorithm
and	O
the	O
Canon	B-Algorithm
EOS-1N	I-Algorithm
RS	I-Algorithm
,	O
but	O
these	O
designs	O
introduce	O
their	O
own	O
problems	O
.	O
</s>
<s>
These	O
pellicle	B-Algorithm
mirrors	I-Algorithm
reduce	O
the	O
amount	O
of	O
light	O
travelling	O
to	O
the	O
film	O
plane	O
or	O
sensor	B-Algorithm
and	O
also	O
can	O
distort	O
the	O
light	O
passing	O
through	O
them	O
,	O
resulting	O
in	O
a	O
less-sharp	O
image	O
.	O
</s>
<s>
To	O
avoid	O
the	O
noise	O
and	O
vibration	O
,	O
many	O
professional	O
cameras	O
offer	O
a	O
mirror	O
lock-up	O
feature	O
,	O
however	O
,	O
this	O
feature	O
totally	O
disables	O
the	O
SLR	B-Algorithm
's	O
automatic	O
focusing	O
ability	O
.	O
</s>
<s>
Electronic	B-Algorithm
viewfinders	I-Algorithm
have	O
the	O
potential	O
to	O
give	O
the	O
'	O
viewing-experience	O
'	O
of	O
a	O
DSLR	B-Device
(	O
through-the-lens	O
viewing	O
)	O
without	O
many	O
of	O
the	O
disadvantages	O
.	O
</s>
<s>
More	O
recently	O
,	O
Sony	O
have	O
resurrected	O
the	O
pellicle	B-Algorithm
mirror	I-Algorithm
concept	O
in	O
their	O
"	O
single-lens	B-Device
translucent	I-Device
"	O
(	O
SLT	O
)	O
range	O
of	O
cameras	O
.	O
</s>
<s>
SLRs	B-Algorithm
vary	O
widely	O
in	O
their	O
construction	O
and	O
typically	O
have	O
bodies	O
made	O
of	O
plastic	O
or	O
magnesium	O
.	O
</s>
<s>
Most	O
manufacturers	O
do	O
not	O
cite	O
durability	O
specifications	O
,	O
but	O
some	O
report	O
shutter	B-Algorithm
life	O
expectancies	O
for	O
professional	O
models	O
.	O
</s>
<s>
For	O
instance	O
,	O
the	O
Canon	O
EOS	O
1Ds	O
MkII	O
is	O
rated	O
for	O
200,000	O
shutter	B-Algorithm
cycles	O
and	O
the	O
Nikon	B-Algorithm
D3	O
is	O
rated	O
for	O
300,000	O
with	O
its	O
exotic	O
carbon	O
fiber/kevlar	O
shutter	B-Algorithm
.	O
</s>
<s>
Because	O
many	O
SLRs	B-Algorithm
have	O
interchangeable	O
lenses	O
,	O
there	O
is	O
a	O
tendency	O
for	O
dust	O
,	O
sand	O
and	O
dirt	O
to	O
get	O
into	O
the	O
main	O
body	O
of	O
the	O
camera	O
through	O
the	O
mirror	O
box	O
when	O
the	O
lens	O
is	O
removed	O
,	O
thus	O
dirtying	O
or	O
even	O
jamming	O
the	O
mirror	O
movement	O
mechanism	O
or	O
the	O
shutter	B-Algorithm
curtain	O
mechanism	O
itself	O
.	O
</s>
<s>
The	O
problem	O
of	O
sensor	B-Algorithm
cleaning	O
has	O
been	O
somewhat	O
reduced	O
in	O
DSLRs	B-Device
as	O
some	O
cameras	O
have	O
a	O
built-in	O
sensor	B-Algorithm
cleaning	O
unit	O
.	O
</s>
<s>
The	O
price	O
of	O
SLRs	B-Algorithm
in	O
general	O
also	O
tends	O
to	O
be	O
somewhat	O
higher	O
than	O
that	O
of	O
other	O
types	O
of	O
cameras	O
,	O
owing	O
to	O
their	O
internal	O
complexity	O
.	O
</s>
<s>
The	O
initial	O
investment	O
in	O
equipment	O
can	O
be	O
prohibitive	O
enough	O
to	O
keep	O
some	O
casual	O
photographers	O
away	O
from	O
SLRs	B-Algorithm
,	O
although	O
the	O
market	O
for	O
used	O
SLRs	B-Algorithm
has	O
become	O
larger	O
particularly	O
as	O
photographers	O
migrate	O
to	O
digital	O
systems	O
.	O
</s>
<s>
The	O
digital	B-Device
single-lens	I-Device
reflex	I-Device
camera	I-Device
has	O
largely	O
replaced	O
the	O
film	O
SLR	B-Algorithm
for	O
its	O
convenience	O
,	O
sales	O
,	O
and	O
popularity	O
at	O
the	O
start	O
of	O
21st	O
century	O
.	O
</s>
<s>
Film-based	O
SLRs	B-Algorithm
are	O
still	O
used	O
by	O
a	O
niche	O
market	O
of	O
enthusiasts	O
and	O
format	O
lovers	O
.	O
</s>
