Absorption

Reflection

Transmission

When light strikes an object then disappears and takes on another form...

A black object such as a T-Shirt will absorb the light and turn it into heat. That's why you will feel hotter in a black shirt in the summer versus a white t-shirt, which will reflect the light.

Direct 

Diffused

No scattering of the light.

An example is a reflection in a

mirror.

Sometimes called “specular

reflection”.

Angle of incident equals

the angle of reflection.

Incident light is reflected

from every part of a surface in many

directions.

When light passes

completely through a material. For

example, glass and water.

Refraction 

Deviation

When a ray of light travels from one

medium into another, its direction

changes. This “bending” of the light is

refraction.

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Angle of Incident is the angle at which light enters an object (like a glass of water) and Angle of Refraction is the angle at which the light bends once it has entered the object...

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It is the path that is perpindicular to the surface.

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This is how much the speed of light is reduced as it enters another medium.

It tells you how much bending power a medium has.

Crown Glass : Refractive Index of 1.50

   Flint Glass : Refractive Index of 1.60

It is used to calculate the amount of bending that will take place.

(n1 sin i = n2 sin r)

Angular change in direction of the

emerging light ray compared to the

incident light ray.

OR

How much the light changes direction once it leaves the medium.

With parallel sides (like a glass) there will be displacement but no deviation.

With Non-Parallel sides (such as a prism) there will be deviation.

When light splits up into its

component parts as when light travels

through a prism, and the different

wavelengths separate to form a

spectrum.

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A lens is a system of one or more

pieces of glass with spherical

surfaces, all of whose centres are on

a common “optical axis”.

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It consists of a single piece of glass.

Consists of several glass components

or lens elements, some of which are

cemented together.

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Takes diverging light

rays from a point source and uses

refraction to bend the light toward a

“focus point” forming a “real” image.

Convex lenses (double and plano) are positive.

Convergent (meniscus) lenses are positive.

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Incident light rays are

diverged even more by refraction so

that the light appears to originate from

a virtual focus point.

Concave lenses (double and plano) are negative lenses.

Divergent (meniscus) are negative lenses.

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Convex

Concave

Plane

Meniscus

They are sometimes called reversed telephoto.

They allow for a longer back focus distance.

Extra lens elements may reduce sharpness.

Extra glass is between the lens and the camera body.

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Extra glass is in front of the lens.

Allows for longer focal distance. 

Gives a narrow field of view and a magnified image.

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They are a simple way to make predictions about an image formation.

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Any problem that

causes the failure of light rays to

converge at one focus point or focal

plane.

The inability of a

lens to bring all the colours to a

common focus.

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Blue and Violet

They also focus closer to the lens.

When different wavelengths are focused at different distances from the lens along the lens axis.

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When wavelengths are focused at different positions in the focal plane...usually the corners.

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It uses Crown glass for the convergent lens and Flint glass for the divergent lens.

(If the lens only uses one type of glass it cannot be achromatic)

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Low dispersion glass.

Other materials with a lower refractive index

Flourite is one example.

It is very expensive.

It brings 2 colour regions to a common focus point. 

Usually red and blue.

When parallel

rays of light do not focus on the same

plane.

A lens with a spherical surface causes

the blurring of a point because it cannot

bring all the light gathered from a single

point to focus at a single point.

The effect is

worse further away from the optical

axis ie. lenses with large diameters.

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Usually lenses with large apertures (fast lenses - small numbers for f#) and wide angle lenses.

The problem can be reduced by limiting the maximum aperture to 5.6

Aspherical lenses must be used.

They are expensive to make.

A Lens having a

free-curved surface which is not

spherical.

Can allow a larger useable

aperture.

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Some

lenses incorporate a set of floating

elements that greatly improve close-up

focusing.

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A type of spherical aberration.

Occurs when rays strike the lens at an

oblique angle and image points of the

lens axis appear comet shaped.

Soft

focus further away from the axis.

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A defect where horizontal lines and

 vertical lines have different focal planes.

Not an issue along the lens axis.

Gets worse further from the lens axis.

Larger apertures increase the effects of

 this problem.

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Barrel

Pincushion

Usually associated with wide angle lenses.

Causes a bulgin in the image.

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Often associated with telephoto zoom lenses.

Causes the image to look pinched. 

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Caused by lenses designed to prevent

barrel distortion.

Keeps vertical lines

straight, but in extreme wide-angle, the

edges of the image appear unnaturally

stretched.

Also not an aberration.

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Refers to the bending, spreading and

interference of waves passing through

an aperture.

In our case, light waves.

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An image of a

“point source” is not a point but a circle

of light.

The Airy disc is a finite size.

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Modulation Transfer Function (MTF)

Indicates how well the lens can

reproduce a likeness of a subject on on

a sensor or film.

Sometimes referred to as its resolving

power.

The reduction of contrast.

A line pair pattern undergoes degradation

as the spatial frequency increases.

In other words the image pattern is degraded in

contrast until the pattern cannot be

distinguished.

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The lines disappear and

become a grey patch.

They show the sharpness of an imaging system or component.

1. Horizontal axis is the distance (mm) from the centre of the image towards one of the corners

Vertical axis is contrast. (1=no contrast reduction) 

2. Black lines: Max Aperture

Blue lines: f/8

3. Solid Line: Sagittal target (S)

Broken LIne: Meridional (M) (Tangential)

4. Bold Lines 10 lines/mm spatial frequency

Thin Lines: 30 lines/mm spatial frequency

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Closer to "1" the better the contrast and

resolving power. 

-if 10 lines/mm (Bold) are.8 or higher, great lens

-if 10 lines/mm (Bold) are .6 to .8 then considered good quality.

-the closer the sagittal (solid) and meridional (broken) curves match, the lower the astigmatism and the better the

background blur.

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This is the “image” of the

aperture, as it appears when one looks

through the front of the lens.

By pivoting the lens at different pivot points

while looking through the lens, or an

image created by the lens.

If the image does not appear to move, then you

have found it.

No Parallax Point (NPP)

If the camera is

rotated along the axis of the tripod mount,

then the images are taken with lens being

at slightly different positions.

52 degrees.

Meaning, it is an angle of view that

appears natural to humans. It is also

approximately the angle of view given by

a “standard lens”.

A standard

lens is one whose focal length is the

same as the diagonal of the sensor or

film frame.

Trigonometry...Pythagorean theorem

A(2)+B(2)=C(2)

eg: 24mm by 36mm

24(2)+36(2)=C(2)

576+1296=C(2)

576+1296=1872

Sqare root of 1872 = 43 

so 43mm

Closest to 43mm is the normal lens...45mm or 50mm

Darkening of the edges of an image.

Light from objects progressively off-axis will encounter more obstructions in the lens.

This results in less “pencil rays” coming from a point source, the further off-axis, the less light travels through the lens from that source.

When stray light (non-imageforming light) enters the lens.

Degrades image clarity by reducing

contrast.

Light from outside the field of view that

hits the front surface of the lens.

This light bounces off the lens barrel and internal lens elements and eventually reaches the sensor.

This is exposure from non image forming light.

An obvious flare pattern that occurs when the sun is within or just outside the field of view.

Creates repeating pattern of a ghost image of the lens aperture or diaphragm. (flare spots)

Lens Shades

Lens Hoods

Bellows Lens Hood 

Your Hand

A Card

Flare Buster

Light that strikes a lens (or any surface) can be reflected, absorbed or refracted.

Some light is reflected away from the

lens. No problem there. (minor light

loss)

Some light is reflected at each lens/air

surface. This reflected light can create

non-image flare.

This flare can bring non-image forming

light to the entire sensor.

This results in a lower luminance

range, or reduced contrast especially

affecting the shadows in the image.

The shape of the aperture.

-Better lenses often have more aperture

blades, and those blades are often curved

to give an aperture that's more circular.

They produce a better bokeh

-Very cheap cameras may use four- or

even three-blade apertures resulting in

square or triangular out-of-focus highlight--

not good bokeh.

A telephoto that is made with internal mirrors to achieve a long focal length in a smaller (shorter) physical sized lens.

Incoming light is reflected forward by the first mirror, then a second mirror reflects it back towards the camera’s sensor.

Used to reduce the illuminance by a known factor in

cameras

Useful when the brightness of the subject is still too

high for the fastest shutter speed and the smallest

aperture.

• Used to reduce the amount of light reaching the sensor

• Neutral means that it allows equal amounts RGB

wavelengths to get through, (or equal amounts filtered

out)

• In other words… no colour balance shift. (Neutral)

• Known “factors” 1 stop, 2 stops, 4 stops, 8 stops etc.

• Allow for wider apertures when there is too much light,

helps decrease depth of field

• Allow for slower shutter speeds when trying to capture

a moving subject and you want to show that movement.

(waterfall, cars, traffic, trees etc.)

A multiplying number that specifies the

change in exposure necessary to compensate for the light

loss caused by the filter.

This filter is used outdoors when the  dynamic range between the sky and the ground is greater than the dynamic range of the sensor or film

•All the parts move independent of each other, so you can

move the lens and the film plane separately

•These movements allow for more control of focus,

distortion and perspective.

•Requires a tripod

•Bulky, heavy

•slow to set-up

•The image on the ground glass is dark

so you need a way to use a focusing

cloth (dark cloth)

•There is no pentaprism, so the image

on the ground glass is upside down and

reversed left to right

•Rise and Fall

•Shift left and right

•Tilts up and down

•Swing toward left and right

If the camera’s lens plane and

film plane are not parallel, then the plane of focus will

meet those two planes in a line

•Correcting for converging lines

•Keeping lines vertical (especially in architecture and

commercial subjects)

They mimic the movements

•Rise and Fall

•Shift left and right

•Tilts up and down

•Swing toward left and right