<s>
The	O
Four	B-Architecture
Thirds	I-Architecture
System	I-Architecture
is	O
a	O
standard	O
created	O
by	O
Olympus	O
and	O
Eastman	O
Kodak	O
for	O
digital	B-Device
single-lens	I-Device
reflex	I-Device
camera	I-Device
(	O
DSLR	B-Device
)	O
and	O
mirrorless	O
camera	O
design	O
and	O
development	O
.	O
</s>
<s>
The	O
system	O
provides	O
a	O
standard	O
that	O
,	O
with	O
digital	B-Device
cameras	I-Device
and	O
lenses	B-Algorithm
available	O
from	O
multiple	O
manufacturers	O
,	O
allows	O
for	O
the	O
interchange	O
of	O
lenses	B-Algorithm
and	O
bodies	O
from	O
different	O
manufacturers	O
.	O
</s>
<s>
Unlike	O
older	O
single-lens	O
reflex	O
(	O
SLR	O
)	O
systems	O
,	O
Four	B-Architecture
Thirds	I-Architecture
was	O
designed	O
from	O
the	O
start	O
to	O
be	O
entirely	O
digital	O
.	O
</s>
<s>
Many	O
lenses	B-Algorithm
are	O
extensively	O
computerised	O
,	O
to	O
the	O
point	O
that	O
Olympus	O
offers	O
firmware	B-Application
updates	O
for	O
many	O
of	O
them	O
.	O
</s>
<s>
The	O
size	B-Algorithm
of	I-Algorithm
the	I-Algorithm
sensor	I-Algorithm
is	O
significantly	O
smaller	O
than	O
for	O
most	O
DSLRs	B-Device
and	O
this	O
implies	O
that	O
lenses	B-Algorithm
,	O
especially	O
telephoto	O
lenses	B-Algorithm
,	O
can	O
be	O
smaller	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
Four	B-Architecture
Thirds	I-Architecture
lens	O
with	O
a	O
300mm	O
focal	B-Algorithm
length	I-Algorithm
would	O
cover	O
about	O
the	O
same	O
angle	O
of	O
view	O
as	O
a	O
600mm	O
focal	B-Algorithm
length	I-Algorithm
lens	O
for	O
the	O
35	O
mm	O
film	O
standard	O
,	O
and	O
is	O
correspondingly	O
more	O
compact	O
.	O
</s>
<s>
Thus	O
,	O
the	O
Four	B-Architecture
Thirds	I-Architecture
System	I-Architecture
has	O
crop	O
factor	O
(	O
focal	B-Algorithm
length	I-Algorithm
multiplier	O
)	O
of	O
about	O
2	O
,	O
and	O
while	O
this	O
enables	O
longer	O
focal	B-Algorithm
length	I-Algorithm
for	O
greater	O
magnification	O
,	O
it	O
does	O
not	O
necessarily	O
aid	O
the	O
manufacture	O
of	O
wide	O
angle	O
lenses	B-Algorithm
.	O
</s>
<s>
The	O
image	B-Algorithm
sensor	I-Algorithm
format	I-Algorithm
,	O
between	O
those	O
of	O
larger	O
SLRs	O
and	O
smaller	O
point-and-shoot	B-Algorithm
compact	O
digital	B-Device
cameras	I-Device
,	O
yields	O
intermediate	O
levels	O
of	O
cost	O
,	O
performance	O
,	O
and	O
convenience	O
.	O
</s>
<s>
The	O
name	O
of	O
the	O
system	O
stems	O
from	O
the	O
size	O
of	O
the	O
image	O
sensor	O
used	O
in	O
the	O
cameras	O
,	O
which	O
is	O
commonly	O
referred	O
to	O
as	O
a	O
4/3	B-Architecture
"	O
type	O
or	O
4/3	B-Architecture
type	O
sensor	O
.	O
</s>
<s>
The	O
imaging	O
area	O
of	O
a	O
Four	B-Architecture
Thirds	I-Architecture
sensor	O
is	O
equal	O
to	O
that	O
of	O
a	O
video	O
camera	O
tube	O
of	O
4/3	B-Architecture
inch	O
diameter	O
.	O
</s>
<s>
The	O
usual	O
size	B-Algorithm
of	I-Algorithm
the	I-Algorithm
sensor	I-Algorithm
is	O
18mm	O
×	O
13.5mm	O
(	O
22.5mm	O
diagonal	O
)	O
,	O
with	O
an	O
imaging	O
area	O
of	O
17.3mm	O
×	O
13.0mm	O
(	O
21.63mm	O
diagonal	O
)	O
.	O
</s>
<s>
The	O
sensor	O
's	O
area	O
is	O
about	O
30	O
–	O
40%	O
smaller	O
than	O
APS-C	B-Algorithm
sensors	O
used	O
in	O
most	O
other	O
DSLRs	B-Device
,	O
but	O
still	O
around	O
9	O
times	O
larger	O
than	O
the	O
1/2.5	O
"	O
sensors	O
typically	O
used	O
in	O
compact	O
digital	B-Device
cameras	I-Device
.	O
</s>
<s>
Incidentally	O
,	O
the	O
imaging	O
area	O
of	O
a	O
Four	B-Architecture
Thirds	I-Architecture
sensor	O
is	O
almost	O
identical	O
to	O
that	O
of	O
110	O
film	O
.	O
</s>
<s>
The	O
emphasis	O
on	O
the	O
4:3	O
image	O
aspect	O
ratio	O
sets	O
Four	B-Architecture
Thirds	I-Architecture
apart	O
from	O
other	O
DSLR	B-Device
systems	O
,	O
which	O
usually	O
adhere	O
to	O
the	O
3:2	O
aspect	O
ratio	O
of	O
the	O
traditional	O
35mm	O
format	O
.	O
</s>
<s>
However	O
,	O
the	O
standard	O
only	O
specifies	O
the	O
sensor	O
diagonal	O
,	O
thus	O
Four	B-Architecture
Thirds	I-Architecture
cameras	O
using	O
the	O
standard	O
3:2	O
aspect	O
ratio	O
would	O
be	O
possible	O
;	O
notably	O
newer	O
Panasonic	O
Micro	B-Operating_System
Four	I-Operating_System
Thirds	I-Operating_System
models	O
even	O
offer	O
shooting	O
at	O
multiple	O
aspect	O
ratios	O
while	O
maintaining	O
the	O
same	O
image	O
diagonal	O
.	O
</s>
<s>
For	O
instance	O
,	O
the	O
Panasonic	B-Device
GH1	I-Device
uses	O
a	O
multi-aspect	O
sensor	O
designed	O
to	O
maximize	O
use	O
of	O
the	O
image	O
circle	O
at	O
4:3	O
,	O
3:2	O
,	O
and	O
16:9	O
;	O
each	O
ratio	O
having	O
a	O
diagonal	O
of	O
22.5mm	O
.	O
</s>
<s>
For	O
example	O
,	O
many	O
lenses	B-Algorithm
designed	O
by	O
Olympus	O
for	O
the	O
Four	B-Architecture
Thirds	I-Architecture
System	I-Architecture
contain	O
internal	O
rectangular	O
baffles	O
or	O
permanently	O
mounted	O
"	O
petal	O
"	O
lens	O
hoods	O
that	O
optimise	O
their	O
operation	O
for	O
the	O
4:3	O
aspect	O
ratio	O
.	O
</s>
<s>
In	O
an	O
interview	O
John	O
Knaur	O
,	O
a	O
Senior	O
Product	O
Manager	O
at	O
Olympus	O
,	O
stated	O
that	O
"	O
The	O
FourThirds	B-Architecture
refers	O
to	O
both	O
the	O
size	O
of	O
the	O
imager	O
and	O
the	O
aspect	O
ratio	O
of	O
the	O
sensor	O
"	O
.	O
</s>
<s>
The	O
smaller	O
sensor	B-Algorithm
size	I-Algorithm
makes	O
possible	O
smaller	O
and	O
lighter	O
camera	O
bodies	O
and	O
lenses	B-Algorithm
.	O
</s>
<s>
In	O
particular	O
,	O
the	O
Four-Thirds	B-Architecture
system	I-Architecture
allows	O
the	O
development	O
of	O
compact	O
,	O
large	O
aperture	O
lenses	B-Algorithm
.	O
</s>
<s>
Corresponding	O
lenses	B-Algorithm
become	O
larger	O
,	O
heavier	O
and	O
more	O
expensive	O
when	O
designed	O
for	O
larger	O
sensor	B-Algorithm
formats	I-Algorithm
.	O
</s>
<s>
Telecentric	O
optical	O
path	O
means	O
that	O
light	O
hitting	O
the	O
sensor	O
is	O
traveling	O
closer	O
to	O
perpendicular	O
to	O
the	O
sensor	O
,	O
resulting	O
in	O
brighter	O
corners	O
,	O
and	O
improved	O
off-center	O
resolution	O
,	O
particularly	O
on	O
wide	O
angle	O
lenses	B-Algorithm
.	O
</s>
<s>
Because	O
the	O
flange	O
focal	O
distance	O
is	O
significantly	O
shorter	O
than	O
those	O
on	O
Canon	O
FD	O
,	O
Canon	O
EF	O
,	O
Nikon	O
F	O
and	O
Pentax	O
K	O
,	O
lenses	B-Algorithm
for	O
many	O
other	O
SLR	O
types	O
including	O
the	O
old	O
Olympus	O
OM	O
System	O
can	O
be	O
fitted	O
to	O
Four	B-Architecture
Thirds	I-Architecture
cameras	O
with	O
simple	O
mechanical	O
adapter	O
rings	O
.	O
</s>
<s>
Compared	O
to	O
a	O
larger	O
sensor	O
with	O
equivalent	O
pixel	O
count	O
,	O
a	O
Four	B-Architecture
Thirds	I-Architecture
sensor	O
gathers	O
disproportionately	O
less	O
light	O
per	O
pixel	O
.	O
</s>
<s>
To	O
get	O
the	O
same	O
angle	O
of	O
view	O
as	O
with	O
a	O
larger	O
sensor	O
,	O
the	O
focal	B-Algorithm
length	I-Algorithm
of	O
the	O
lens	O
used	O
with	O
a	O
Four	B-Architecture
Thirds	I-Architecture
sensor	O
needs	O
to	O
be	O
shorter	O
.	O
</s>
<s>
In	O
other	O
words	O
,	O
the	O
focal	O
ratio	O
of	O
the	O
lens	O
must	O
be	O
smaller	O
on	O
the	O
Four	B-Architecture
Thirds	I-Architecture
system	I-Architecture
to	O
give	O
the	O
same	O
depth	O
of	O
field	O
and	O
image	O
noise	O
.	O
</s>
<s>
Since	O
it	O
is	O
more	O
difficult	O
to	O
produce	O
faster	O
lenses	B-Algorithm
(	O
lenses	B-Algorithm
with	O
smaller	O
focal	O
ratios	O
)	O
,	O
it	O
can	O
be	O
difficult	O
or	O
impossible	O
to	O
find	O
a	O
lens	O
that	O
produces	O
as	O
shallow	O
a	O
depth	O
of	O
field	O
,	O
and	O
gathers	O
as	O
much	O
light	O
,	O
as	O
an	O
equivalent	O
lens	O
on	O
larger	O
formats	O
.	O
</s>
<s>
For	O
instance	O
,	O
a	O
35mm	O
"	O
full-frame	O
"	O
DSLR	B-Device
can	O
match	O
the	O
depth	O
of	O
field	O
of	O
a	O
Four	B-Architecture
Thirds	I-Architecture
camera	O
by	O
closing	O
down	O
the	O
aperture	O
by	O
two	O
stops	O
;	O
but	O
it	O
may	O
be	O
more	O
difficult	O
or	O
impossible	O
for	O
a	O
Four	B-Architecture
Thirds	I-Architecture
System	I-Architecture
to	O
match	O
the	O
shallow	O
depth	O
of	O
field	O
of	O
a	O
35mm	O
camera	O
using	O
a	O
fast	O
lens	O
.	O
</s>
<s>
Most	O
Four	B-Architecture
Thirds	I-Architecture
cameras	O
(	O
notably	O
those	O
manufactured	O
by	O
Olympus	O
)	O
use	O
an	O
aspect	O
ratio	O
of	O
4:3	O
rather	O
than	O
3:2	O
;	O
newer	O
models	O
offer	O
cropping	O
to	O
3:2	O
,	O
but	O
this	O
results	O
in	O
a	O
reduced	O
image	O
diagonal	O
(	O
i.e.	O
,	O
the	O
effective	O
crop	O
factor	O
is	O
then	O
2.08	O
)	O
.	O
</s>
<s>
As	O
of	O
the	O
2006	O
Photo	O
Marketing	O
Association	O
Annual	O
Convention	O
and	O
Trade	O
Show	O
,	O
the	O
Four	B-Architecture
Thirds	I-Architecture
consortium	O
consisted	O
of	O
the	O
following	O
companies	O
:	O
</s>
<s>
Olympus	O
and	O
Leica/Panasonic	O
have	O
made	O
dedicated	O
Four	B-Architecture
Thirds	I-Architecture
lenses	B-Algorithm
,	O
and	O
Sigma	O
makes	O
adapted	O
versions	O
of	O
their	O
"	O
DC	O
"	O
lenses	B-Algorithm
for	O
APS-C	B-Algorithm
format	O
DSLRs	B-Device
.	O
</s>
<s>
Kodak	O
once	O
sold	O
sensors	O
to	O
Olympus	O
for	O
use	O
in	O
their	O
Four	B-Architecture
Thirds	I-Architecture
bodies	O
,	O
but	O
the	O
newer	O
Olympus	O
Four	B-Architecture
Thirds	I-Architecture
cameras	O
used	O
Panasonic	O
sensors	O
.	O
</s>
<s>
The	O
majority	O
of	O
Four	B-Architecture
Thirds	I-Architecture
System	I-Architecture
cameras	O
and	O
Four	B-Architecture
Thirds	I-Architecture
lenses	B-Algorithm
are	O
made	O
by	O
Olympus	O
.	O
</s>
<s>
Many	O
Four	B-Architecture
Thirds	I-Architecture
cameras	O
use	O
"	O
sensor-shift	O
"	O
in-body	O
image	O
stabilization	O
,	O
making	O
the	O
need	O
for	O
image	O
stabilization	O
technology	O
in	O
its	O
lenses	B-Algorithm
unnecessary	O
.	O
</s>
<s>
All	O
Four	B-Architecture
Thirds	I-Architecture
cameras	O
also	O
incorporate	O
an	O
automatic	O
sensor	O
cleaning	O
device	O
,	O
in	O
which	O
a	O
thin	O
glass	O
filter	O
in	O
front	O
of	O
the	O
sensor	O
vibrates	O
at	O
30kHz	O
,	O
causing	O
dust	O
to	O
fall	O
off	O
and	O
adhere	O
to	O
a	O
piece	O
of	O
sticky	O
material	O
below	O
.	O
</s>
<s>
Olympus	O
 '	O
E-system	O
camera	O
bodies	O
are	O
noted	O
for	O
their	O
inclusion	O
of	O
a	O
wide	O
range	O
of	O
firmware-level	O
features	O
and	O
customization	O
,	O
good	O
JPEG	O
engine	O
,	O
and	O
compact	O
size	O
.	O
</s>
<s>
Because	O
of	O
the	O
smaller	O
format	O
of	O
Four	B-Architecture
Thirds	I-Architecture
,	O
the	O
viewfinders	O
tend	O
to	O
be	O
smaller	O
than	O
on	O
comparable	O
cameras	O
.	O
</s>
<s>
Manufacture	O
of	O
Four	B-Architecture
Thirds	I-Architecture
cameras	O
came	O
to	O
an	O
end	O
after	O
the	O
introduction	O
of	O
the	O
mirrorless	O
Micro	B-Operating_System
Four	I-Operating_System
Thirds	I-Operating_System
format	O
.	O
</s>
<s>
The	O
Four	B-Architecture
Thirds	I-Architecture
lens	B-Algorithm
mount	I-Algorithm
is	O
specified	O
to	O
be	O
a	O
bayonet	O
type	O
with	O
a	O
flange	O
focal	O
distance	O
of	O
38.67mm	O
.	O
</s>
<s>
There	O
are	O
currently	O
around	O
three	O
dozen	O
lenses	B-Algorithm
for	O
the	O
Four	B-Architecture
Thirds	I-Architecture
System	I-Architecture
standard	O
.	O
</s>
<s>
Before	O
announcing	O
that	O
it	O
would	O
stop	O
production	O
of	O
Four	B-Architecture
Thirds	I-Architecture
lenses	B-Algorithm
in	O
early	O
2017	O
,	O
Olympus	O
produced	O
about	O
20	O
lenses	B-Algorithm
for	O
the	O
Four	B-Architecture
Thirds	I-Architecture
System	I-Architecture
under	O
their	O
"	O
Zuiko	B-Device
Digital	I-Device
"	O
brand	O
.	O
</s>
<s>
High	O
Grade	O
lenses	B-Algorithm
have	O
faster	O
maximum	O
apertures	O
,	O
but	O
are	O
significantly	O
more	O
expensive	O
and	O
larger	O
,	O
and	O
the	O
Super	O
High	O
Grade	O
zooms	O
have	O
constant	O
maximum	O
aperture	O
over	O
the	O
full	O
zoom	O
range	O
;	O
all	O
but	O
the	O
Standard	O
grade	O
are	O
weather-sealed	O
.	O
</s>
<s>
Lenses	B-Algorithm
within	O
each	O
grade	O
cover	O
the	O
range	O
from	O
wide-angle	O
to	O
super	O
telephoto	O
.	O
</s>
<s>
The	O
Zuiko	B-Device
Digital	I-Device
lenses	B-Algorithm
are	O
well	O
regarded	O
for	O
their	O
consistently	O
good	O
optics	O
.	O
</s>
<s>
The	O
following	O
table	O
lists	O
all	O
Zuiko	B-Device
Digital	I-Device
lenses	B-Algorithm
available	O
at	O
the	O
time	O
Olympus	O
stopped	O
Four	B-Architecture
Thirds	I-Architecture
production	O
:	O
</s>
<s>
Sigma	O
has	O
adapted	O
13	O
lenses	B-Algorithm
for	O
the	O
Four	B-Architecture
Thirds	I-Architecture
System	I-Architecture
,	O
ranging	O
from	O
10mm	O
to	O
800mm	O
,	O
including	O
several	O
for	O
which	O
no	O
equivalent	O
exists	O
:	O
the	O
fast	O
primes	O
(	O
30mm	O
and	O
50mm	O
)	O
and	O
extreme	O
telephoto	O
(	O
300	O
–	O
800mm	O
5.6	O
)	O
.	O
</s>
<s>
As	O
of	O
2014	O
all	O
Sigma	O
lenses	B-Algorithm
for	O
the	O
Four	B-Architecture
Thirds	I-Architecture
System	I-Architecture
have	O
been	O
discontinued	O
.	O
</s>
<s>
Leica	O
has	O
designed	O
four	O
lenses	B-Algorithm
for	O
the	O
Four	B-Architecture
Thirds	I-Architecture
System	I-Architecture
:	O
fast	O
and	O
slow	O
normal	O
zooms	O
and	O
a	O
14	O
–	O
150mm	O
super-zoom	O
,	O
all	O
with	O
Panasonic	O
's	O
image	O
stabilization	O
system	O
,	O
and	O
an	O
unstabilized	O
25mm	O
prime	O
.	O
</s>
<s>
An	O
official	O
list	O
of	O
available	O
lenses	B-Algorithm
can	O
be	O
found	O
on	O
Four-Thirds.org	O
web	O
site	O
.	O
</s>
<s>
As	O
for	O
the	O
system	O
itself	O
,	O
it	O
was	O
silently	O
discontinued	O
in	O
favor	O
of	O
the	O
Micro	B-Operating_System
Four	I-Operating_System
Thirds	I-Operating_System
System	I-Operating_System
.	O
</s>
<s>
In	O
August	O
2008	O
,	O
Olympus	O
and	O
Panasonic	O
introduced	O
a	O
new	O
format	O
,	O
Micro	B-Operating_System
Four	I-Operating_System
Thirds	I-Operating_System
.	O
</s>
<s>
A	O
live	B-Device
preview	I-Device
is	O
shown	O
on	O
either	O
the	O
camera	O
's	O
main	O
liquid-crystal	B-Device
display	I-Device
or	O
via	O
an	O
electronic	B-Algorithm
viewfinder	I-Algorithm
,	O
as	O
in	O
digital	O
compact	B-Algorithm
cameras	I-Algorithm
.	O
</s>
<s>
Autofocus	O
may	O
be	O
accomplished	O
via	O
a	O
contrast	O
detection	O
process	O
using	O
the	O
main	O
imager	O
,	O
again	O
similar	O
to	O
digital	O
compact	B-Algorithm
cameras	I-Algorithm
.	O
</s>
<s>
The	O
goal	O
of	O
the	O
new	O
system	O
was	O
to	O
allow	O
for	O
even	O
smaller	O
cameras	O
,	O
competing	O
directly	O
with	O
higher-end	O
point-and-shoot	B-Algorithm
compact	O
digital	B-Device
cameras	I-Device
and	O
DSLRs	B-Device
.	O
</s>
<s>
The	O
smaller	O
flange	O
focal	O
distance	O
allows	O
for	O
more	O
compact	O
normal	O
and	O
wide	O
angle	O
lenses	B-Algorithm
.	O
</s>
<s>
It	O
also	O
facilitates	O
the	O
use	O
,	O
with	O
an	O
adapter	O
,	O
of	O
lenses	B-Algorithm
based	O
on	O
other	O
mounting	O
systems	O
,	O
including	O
many	O
manual	O
focus	O
lenses	B-Algorithm
from	O
the	O
seventies	O
and	O
eighties	O
.	O
</s>
<s>
In	O
particular	O
,	O
Four	B-Architecture
Thirds	I-Architecture
lenses	B-Algorithm
can	O
be	O
used	O
on	O
Micro	B-Operating_System
Four	I-Operating_System
Thirds	I-Operating_System
bodies	O
with	O
an	O
adapter	O
;	O
however	O
,	O
"	O
all	O
of	O
the	O
functions	O
of	O
the	O
Micro	B-Operating_System
Four	I-Operating_System
Thirds	I-Operating_System
System	I-Operating_System
may	O
not	O
always	O
be	O
available.	O
"	O
</s>
