useful for optometry science,photography..

1. STOPS PUPILS AND
PORTS

2. INTRODUCTION
• When an optical instrument is used to study an
object,the light reflected from the object enters
the instrument through various lenses.
• Here Apertures control the amount of light that
gets into an optical system and hence the
intensity of the image formed by the system.
• stops are physical apertures that limit the rays
through a system

4. Aperture stops
• The limiting diameter which determines the
amount of light which reaches the imaging
area is called the aperture stop
• Usually located within the lens (single
element) or within the multi element
system.

5. • In any real optical system there are multiple apertures, but
only one, the aperture stop,determines which rays
traverse the system and, as result, the intensity of
images.
• Adjustable stops are commonly created from thin metallic
leaf structures to determine the amount of light which
reaches a film

6. PUPIL
• Formally, a pupil is an image of
the aperture stop.
• There are 2 types of pupils
– 1.Entrance pupil
– 2.Exit pupil

7. ENTRANCE PUPIL
• The entrance pupil of a system is the image
of the aperture stop as seen from a point
on the optic axis in the object plane.
• The entrance pupil takes over the role of
the lens rim in the simple camera

9. • In the illustration, the physical aperture is behind the lens.
You can see that more light will get through the physical
aperture behind the lens than would have if the lens were
not present. The extreme ray is one that is refracted by
the lens so that it just passes through the aperture.
Tracing the projected path of that extreme ray without the
lens, you can see that the entrance pupil is the size
aperture that would be required to pass that extreme ray
in the absence of the lens

10. EXIT PUPIL
• The exit pupil of a system is the image of
the aperture stop as seen from a point on
the optic axis in the image plane.
• In a telescope or compound microscope,
this image is the image of
the objective element(s) as produced by
the eyepiece.
• It is a virtual aperture in an optical system.

12. EXIT PUPIL
In this case where the physical aperture stop is
in front of the lens, the exit pupil is the image of
that aperture stop as seen from the optic axis in
the image plane, looking back through the lens.
In this case the entrance pupil is just the
physical aperture since there is no lens
intervening from the standpoint of the object.

13. FIELD OF VIEW QUANTITIES
Components in the optical system that limits
the amount or size of the object that can
actually be imaged and is relevent when
you are concerned with off axis or extented
object.

14. Field of view quantities
• Entrance port (object space)
• Field stop (device)
• Exit port (image space)

15. FIELD STOPS
• The element that limits the size or angular
breadth of an object that can be imaged by
the system is called the field stop.
• For cameras, the size of the film or CCD
detector determines the maximum image
size and serves as the field stop.
• Usually located at the focal
plane

16. Entrance port
• -The image of the F.S. formed by any lens
in front of it
• -If no lens is in front of it, then the F.S. and
the Entrance Port are the same device
• -Object space quantity that makes the
smallest angle relative to the entrance pupil

17. Exit port
• The image of the F.S. formed by any lens
behind it
• -If no lens is behind it, then the F.S. and the
Exit port are the same device
• -Image space quantity that makes the
smallest angle relative to the entrance pupil

18. Vignetting
• Rays that don’t make it through an optical system
are said to be vignetted (shadowed)
– maybe a lens isn’t big enough
– maybe your eye’s pupil isn’t big enough, or is
improperly placed
• Often appears as a gradual darkening as a
function of distance from the field center
– the farther out you go, the bigger your lenses need to
be
– every optical system has a limited (unvignetted) field of
view
– beyond this, throughput goes down

21. The depth of field
• A camera can only focus its lens at a single
point, but there will be an area that
stretches in front of and behind this focus
point that still appears sharp.
• This zone is known as the depth of field. It’s
not a fixed distance, it changes in size and
can be described as either ‘shallow’ (where
only a narrow zone appears sharp) or deep
(where more of the picture appears sharp).

24. Depth of focus
• It is the depth inside the camera, at the
sensor position, within which the image can
be considered acceptably sharp.
• Almost always, Depth of Field is the thing
photographers are interested in. Depth of
Focus can be considered an advanced or
specialist topic.