- Source: Angular aperture
The angular aperture of a lens is the angular size of the lens aperture as seen from the focal point:
a
=
2
arctan
(
D
/
2
f
)
=
2
arctan
(
D
2
f
)
{\displaystyle a=2\arctan \left({\frac {D/2}{f}}\right)=2\arctan \left({\frac {D}{2f}}\right)}
where
f
{\displaystyle f}
is the focal length
D
{\displaystyle D}
is the diameter of the aperture.
Relation to numerical aperture
In a medium with an index of refraction close to 1, such as air, the angular aperture is approximately equal to twice the numerical aperture of the lens.
Formally, the numerical aperture in air is:
N
A
=
sin
a
/
2
=
sin
arctan
(
D
2
f
)
{\displaystyle \mathrm {NA} =\sin a/2=\sin \arctan \left({\frac {D}{2f}}\right)}
In the paraxial approximation, with a small aperture,
D
<
f
{\displaystyle D
:
N
A
≈
a
/
2
{\displaystyle \mathrm {NA} \approx a/2}
References
See also
f-number
Numerical aperture
Acceptance angle, half the angular aperture
Field of view
Kata Kunci Pencarian:
- Tingkap numeris
- Interferometer astronomi
- Teleskop Hobby–Eberly
- Daftar istilah fotografi
- Angular aperture
- Angular resolution
- Numerical aperture
- Angular diameter
- Acceptance angle
- Aperture synthesis
- Acceptance angle (solar concentrator)
- Cambridge Optical Aperture Synthesis Telescope
- Kaleidoscope
- Magnification
