<s>
A	O
pinhole	B-Algorithm
camera	I-Algorithm
is	O
a	O
simple	O
camera	O
without	O
a	O
lens	O
but	O
with	O
a	O
tiny	O
aperture	B-General_Concept
(	O
the	O
so-called	O
pinhole	O
)	O
—	O
effectively	O
a	O
light-proof	O
box	O
with	O
a	O
small	O
hole	O
in	O
one	O
side	O
.	O
</s>
<s>
Light	O
from	O
a	O
scene	O
passes	O
through	O
the	O
aperture	B-General_Concept
and	O
projects	O
an	O
inverted	O
image	O
on	O
the	O
opposite	O
side	O
of	O
the	O
box	O
,	O
which	O
is	O
known	O
as	O
the	O
camera	B-Algorithm
obscura	I-Algorithm
effect	O
.	O
</s>
<s>
The	O
camera	B-Algorithm
obscura	I-Algorithm
or	O
pinhole	O
image	O
is	O
a	O
natural	O
optical	O
phenomenon	O
.	O
</s>
<s>
Ibn	O
al-Haytham	O
(	O
965	O
–	O
1039	O
)	O
,	O
an	O
Arab	O
physicist	O
also	O
known	O
as	O
Alhazen	O
,	O
described	O
the	O
camera	B-Algorithm
obscura	I-Algorithm
effect	O
.	O
</s>
<s>
Over	O
the	O
centuries	O
others	O
started	O
to	O
experiment	O
with	O
it	O
,	O
mainly	O
in	O
dark	O
rooms	O
with	O
a	O
small	O
opening	O
in	O
shutters	O
,	O
mostly	O
to	O
study	O
the	O
nature	O
of	O
light	O
and	O
to	O
safely	O
watch	O
solar	B-Application
eclipses	I-Application
.	O
</s>
<s>
In	O
the	O
17th	O
century	O
,	O
the	O
camera	B-Algorithm
obscura	I-Algorithm
with	O
a	O
lens	O
became	O
a	O
popular	O
drawing	O
aid	O
that	O
was	O
further	O
developed	O
into	O
a	O
mobile	O
device	O
,	O
first	O
in	O
a	O
little	O
tent	O
and	O
later	O
in	O
a	O
box	O
.	O
</s>
<s>
The	O
photographic	O
camera	O
,	O
as	O
developed	O
early	O
in	O
the	O
19th	O
century	O
,	O
was	O
basically	O
an	O
adaptation	O
of	O
the	O
box-type	O
camera	B-Algorithm
obscura	I-Algorithm
with	O
a	O
lens	O
.	O
</s>
<s>
The	O
first	O
known	O
description	O
of	O
pinhole	B-Algorithm
photography	I-Algorithm
is	O
found	O
in	O
the	O
1856	O
book	O
The	O
Stereoscope	O
by	O
Scottish	O
inventor	O
David	O
Brewster	O
,	O
including	O
the	O
description	O
of	O
the	O
idea	O
as	O
"	O
a	O
camera	O
without	O
lenses	O
,	O
and	O
with	O
only	O
a	O
pin-hole	O
"	O
.	O
</s>
<s>
Eugène	O
Estanave	O
experimented	O
with	O
integral	B-Algorithm
photography	I-Algorithm
,	O
exhibiting	O
a	O
result	O
in	O
1925	O
and	O
publishing	O
his	O
findings	O
in	O
La	O
Nature	O
.	O
</s>
<s>
The	O
image	O
of	O
a	O
pinhole	B-Algorithm
camera	I-Algorithm
may	O
be	O
projected	O
onto	O
a	O
translucent	O
screen	O
for	O
a	O
real-time	O
viewing	O
(	O
used	O
for	O
safe	O
observation	O
of	O
solar	B-Application
eclipses	I-Application
)	O
or	O
to	O
trace	O
the	O
image	O
on	O
paper	O
.	O
</s>
<s>
But	O
it	O
is	O
more	O
often	O
used	O
without	O
a	O
translucent	O
screen	O
for	O
pinhole	B-Algorithm
photography	I-Algorithm
with	O
photographic	O
film	O
or	O
photographic	O
paper	O
placed	O
on	O
the	O
surface	O
opposite	O
to	O
the	O
pinhole	O
aperture	B-General_Concept
.	O
</s>
<s>
A	O
common	O
use	O
of	O
pinhole	B-Algorithm
photography	I-Algorithm
is	O
to	O
capture	O
the	O
movement	O
of	O
the	O
sun	O
over	O
a	O
long	O
period	O
of	O
time	O
.	O
</s>
<s>
Pinhole	B-Algorithm
photography	I-Algorithm
is	O
used	O
for	O
artistic	O
reasons	O
,	O
but	O
also	O
for	O
educational	O
purposes	O
to	O
let	O
pupils	O
learn	O
about	O
,	O
and	O
experiment	O
with	O
,	O
the	O
basics	O
of	O
photography	O
.	O
</s>
<s>
Pinhole	B-Algorithm
cameras	I-Algorithm
with	O
CCDs	O
(	O
charge-coupled	B-Algorithm
devices	I-Algorithm
)	O
are	O
sometimes	O
used	O
for	O
surveillance	O
because	O
they	O
are	O
difficult	O
to	O
detect	O
.	O
</s>
<s>
Related	O
cameras	O
,	O
image	O
forming	O
devices	O
,	O
or	O
developments	O
from	O
it	O
include	O
Franke	O
's	O
widefield	O
pinhole	B-Algorithm
camera	I-Algorithm
,	O
the	O
pinspeck	B-Algorithm
camera	I-Algorithm
,	O
and	O
the	O
pinhead	B-Algorithm
mirror	I-Algorithm
.	O
</s>
<s>
Modern	O
manufacturing	O
has	O
enabled	O
the	O
production	O
of	O
high	O
quality	O
pinhole	O
lenses	O
that	O
can	O
be	O
applied	O
to	O
digital	O
cameras	O
;	O
allowing	O
photographers	O
and	O
videographers	O
to	O
achieve	O
the	O
camera	B-Algorithm
obscura	I-Algorithm
effect	O
.	O
</s>
<s>
As	O
pinhole	O
photographs	O
have	O
nearly	O
infinite	B-Application
depth	O
of	O
field	O
,	O
everything	O
appears	O
in	O
focus	O
.	O
</s>
<s>
Other	O
special	O
features	O
can	O
be	O
built	O
into	O
pinhole	B-Algorithm
cameras	I-Algorithm
such	O
as	O
the	O
ability	O
to	O
take	O
double	O
images	O
by	O
using	O
multiple	O
pinholes	O
,	O
or	O
the	O
ability	O
to	O
take	O
pictures	O
in	O
cylindrical	O
or	O
spherical	O
perspective	O
by	O
curving	O
the	O
film	O
plane	O
.	O
</s>
<s>
Pinhole	B-Algorithm
cameras	I-Algorithm
can	O
be	O
handmade	O
by	O
the	O
photographer	O
for	O
a	O
particular	O
purpose	O
.	O
</s>
<s>
In	O
its	O
simplest	O
form	O
,	O
the	O
photographic	O
pinhole	B-Algorithm
camera	I-Algorithm
can	O
consist	O
of	O
a	O
light-tight	O
box	O
with	O
a	O
pinhole	O
in	O
one	O
end	O
,	O
and	O
a	O
piece	O
of	O
film	O
or	O
photographic	O
paper	O
wedged	O
or	O
taped	O
into	O
the	O
other	O
end	O
.	O
</s>
<s>
A	O
cylindrical	O
oatmeal	O
container	O
may	O
be	O
made	O
into	O
a	O
pinhole	B-Algorithm
camera	I-Algorithm
.	O
</s>
<s>
The	O
interior	O
of	O
an	O
effective	O
pinhole	B-Algorithm
camera	I-Algorithm
is	O
black	O
to	O
avoid	O
any	O
reflection	O
of	O
the	O
entering	O
light	O
onto	O
the	O
photographic	O
material	O
or	O
viewing	O
screen	O
.	O
</s>
<s>
Pinhole	B-Algorithm
cameras	I-Algorithm
can	O
be	O
constructed	O
with	O
a	O
sliding	O
film	O
holder	O
or	O
back	O
so	O
the	O
distance	O
between	O
the	O
film	O
and	O
the	O
pinhole	O
can	O
be	O
adjusted	O
.	O
</s>
<s>
Pinhole	B-Algorithm
cameras	I-Algorithm
can	O
also	O
be	O
constructed	O
by	O
replacing	O
the	O
lens	O
assembly	O
in	O
a	O
conventional	O
camera	O
with	O
a	O
pinhole	O
.	O
</s>
<s>
In	O
particular	O
,	O
compact	O
35mm	O
cameras	O
whose	O
lens	O
and	O
focusing	O
assembly	O
have	O
been	O
damaged	O
can	O
be	O
reused	O
as	O
pinhole	B-Algorithm
cameras	I-Algorithm
—	O
maintaining	O
the	O
use	O
of	O
the	O
shutter	O
and	O
film	O
winding	O
mechanisms	O
.	O
</s>
<s>
Use	O
with	O
a	O
digital	B-Device
SLR	I-Device
allows	O
metering	O
and	O
composition	O
by	O
trial	O
and	O
error	O
,	O
and	O
is	O
effectively	O
free	O
,	O
so	O
is	O
a	O
popular	O
way	O
to	O
try	O
pinhole	B-Algorithm
photography	I-Algorithm
.	O
</s>
<s>
Optimally	O
,	O
the	O
size	O
of	O
the	O
aperture	B-General_Concept
should	O
be	O
1/100	O
or	O
less	O
of	O
the	O
distance	O
between	O
it	O
and	O
the	O
projected	O
image	O
.	O
</s>
<s>
Within	O
limits	O
,	O
a	O
small	O
pinhole	O
through	O
a	O
thin	O
surface	O
will	O
result	O
in	O
a	O
sharper	O
image	B-Algorithm
resolution	I-Algorithm
because	O
the	O
projected	O
circle	O
of	O
confusion	O
at	O
the	O
image	O
plane	O
is	O
practically	O
the	O
same	O
size	O
as	O
the	O
pinhole	O
.	O
</s>
<s>
The	O
smallest	O
possible	O
diameter	O
of	O
the	O
image	O
point	O
and	O
therefore	O
the	O
highest	O
possible	O
image	B-Algorithm
resolution	I-Algorithm
and	O
the	O
sharpest	O
image	O
are	O
given	O
when	O
:	O
</s>
<s>
(	O
Where	O
d	O
is	O
the	O
pinhole	O
diameter	O
,	O
f	O
is	O
the	O
distance	O
from	O
pinhole	O
to	O
image	O
plane	O
or	O
“	O
focal	B-Algorithm
length	I-Algorithm
”	O
and	O
λ	O
is	O
the	O
wavelength	O
of	O
light	O
.	O
)	O
</s>
<s>
The	O
correct	O
optimum	O
can	O
be	O
found	O
with	O
Fraunhofer	O
approximation	O
of	O
the	O
diffraction	O
pattern	O
behind	O
a	O
circular	O
aperture	B-General_Concept
at	O
:	O
</s>
<s>
The	O
depth	O
of	O
field	O
is	O
basically	O
infinite	B-Application
,	O
but	O
this	O
does	O
not	O
mean	O
that	O
no	O
optical	O
blurring	O
occurs	O
.	O
</s>
<s>
The	O
infinite	B-Application
depth	O
of	O
field	O
means	O
that	O
image	O
blur	O
depends	O
not	O
on	O
object	O
distance	O
but	O
on	O
other	O
factors	O
,	O
such	O
as	O
the	O
distance	O
from	O
the	O
aperture	B-General_Concept
to	O
the	O
film	O
plane	O
,	O
the	O
aperture	B-General_Concept
size	O
,	O
the	O
wavelength(s )	O
of	O
the	O
light	O
source	O
,	O
and	O
motion	O
of	O
the	O
subject	O
or	O
canvas	O
.	O
</s>
<s>
Additionally	O
,	O
pinhole	B-Algorithm
photography	I-Algorithm
can	O
not	O
avoid	O
the	O
effects	O
of	O
haze	B-Device
.	O
</s>
<s>
In	O
the	O
1970s	O
,	O
Young	O
measured	O
the	O
resolution	O
limit	O
of	O
the	O
pinhole	B-Algorithm
camera	I-Algorithm
as	O
a	O
function	O
of	O
pinhole	O
diameter	O
and	O
later	O
published	O
a	O
tutorial	O
in	O
The	O
Physics	O
Teacher	O
.	O
</s>
<s>
Partly	O
to	O
enable	O
a	O
variety	O
of	O
diameters	O
and	O
focal	B-Algorithm
lengths	I-Algorithm
,	O
he	O
defined	O
two	O
normalized	O
variables	O
:	O
resolution	O
limit	O
divided	O
by	O
the	O
pinhole	O
radius	O
,	O
and	O
focal	B-Algorithm
length	I-Algorithm
divided	O
by	O
the	O
quantity	O
s2/λ	O
,	O
where	O
s	O
is	O
the	O
radius	O
of	O
the	O
pinhole	O
and	O
λ	O
is	O
the	O
wavelength	O
of	O
the	O
light	O
,	O
typically	O
about	O
550nm	O
.	O
</s>
<s>
In	O
the	O
region	O
of	O
near-field	O
diffraction	O
(	O
or	O
Fresnel	O
diffraction	O
)	O
,	O
the	O
pinhole	O
focuses	O
the	O
light	O
slightly	O
,	O
and	O
the	O
resolution	O
limit	O
is	O
minimized	O
when	O
the	O
focal	B-Algorithm
length	I-Algorithm
f	O
(	O
the	O
distance	O
between	O
the	O
pinhole	O
and	O
the	O
film	O
plane	O
)	O
is	O
given	O
by	O
f	O
=	O
s2/λ	O
.	O
</s>
<s>
At	O
this	O
focal	B-Algorithm
length	I-Algorithm
,	O
the	O
pinhole	O
focuses	O
the	O
light	O
slightly	O
,	O
and	O
the	O
resolution	O
limit	O
is	O
about	O
2/3	O
of	O
the	O
radius	O
of	O
the	O
pinhole	O
.	O
</s>
<s>
The	O
value	O
s2/λ	O
is	O
in	O
a	O
sense	O
the	O
natural	O
focal	B-Algorithm
length	I-Algorithm
of	O
the	O
pinhole	O
.	O
</s>
<s>
The	O
f-number	O
of	O
the	O
camera	O
may	O
be	O
calculated	O
by	O
dividing	O
the	O
distance	O
from	O
the	O
pinhole	O
to	O
the	O
imaging	O
plane	O
(	O
the	O
focal	B-Algorithm
length	I-Algorithm
)	O
by	O
the	O
diameter	O
of	O
the	O
pinhole	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
camera	O
with	O
a	O
0.5mm	O
diameter	O
pinhole	O
,	O
and	O
a	O
50mm	O
focal	B-Algorithm
length	I-Algorithm
would	O
have	O
an	O
f-number	O
of	O
50/0.5	O
,	O
or	O
100	O
(	O
f/100	O
in	O
conventional	O
notation	O
)	O
.	O
</s>
<s>
Due	O
to	O
the	O
large	O
f-number	O
of	O
a	O
pinhole	B-Algorithm
camera	I-Algorithm
,	O
exposures	O
will	O
often	O
encounter	O
reciprocity	O
failure	O
.	O
</s>
<s>
Because	O
a	O
pinhole	B-Algorithm
camera	I-Algorithm
requires	O
a	O
lengthy	O
exposure	O
,	O
its	O
shutter	O
may	O
be	O
manually	O
operated	O
,	O
as	O
with	O
a	O
flap	O
made	O
of	O
opaque	O
material	O
to	O
cover	O
and	O
uncover	O
the	O
pinhole	O
.	O
</s>
<s>
A	O
non-focusing	O
coded-aperture	O
optical	O
system	O
may	O
be	O
thought	O
of	O
as	O
multiple	O
pinhole	B-Algorithm
cameras	I-Algorithm
in	O
conjunction	O
.	O
</s>
<s>
However	O
,	O
multiple	O
images	O
are	O
formed	O
,	O
usually	O
requiring	O
computer	O
deconvolution	B-Algorithm
.	O
</s>
<s>
A	O
revival	O
in	O
popularity	O
has	O
become	O
evident	O
in	O
recent	O
years	O
with	O
the	O
success	O
of	O
Kickstarter	O
crowdfunding	O
campaigns	O
offering	O
a	O
range	O
of	O
pinhole	B-Algorithm
photography	I-Algorithm
products	O
.	O
</s>
<s>
Projects	O
have	O
included	O
a	O
camera	O
crafted	O
from	O
wood	O
and	O
the	O
Pinhole	O
Pro	O
,	O
a	O
lens	O
designed	O
for	O
DSLR	B-Device
and	O
MILC	O
digital	O
cameras	O
.	O
</s>
<s>
A	O
pinhole	B-Algorithm
camera	I-Algorithm
effect	O
can	O
sometimes	O
occur	O
naturally	O
.	O
</s>
<s>
During	O
an	O
eclipse	B-Application
,	O
this	O
produces	O
small	O
crescents	O
in	O
the	O
case	O
of	O
a	O
partial	O
eclipse	B-Application
,	O
or	O
hollow	O
rings	O
in	O
the	O
case	O
of	O
an	O
annular	O
eclipse	B-Application
.	O
</s>
<s>
Worldwide	O
Pinhole	B-Algorithm
Photography	I-Algorithm
Day	O
is	O
observed	O
on	O
the	O
last	O
Sunday	O
of	O
April	O
,	O
every	O
year	O
.	O
</s>
