dimanche 2 décembre 2012
dimanche 12 août 2012
FLASH
While multiple flash units increase creative
possibilities mixing primary flash with ambient natural light can produce very
good result. Using a single flash it’s important to keep the unit relatively close
to the subject so that it’s not operating at maximum capacity for each shot,
this will increase the range of exposure settings that can be set.
Where should I position the flash
The flash should be positioned opposite
the main light source, off camera at an angle of around 45 degree. This will
help to prevent red-eye as well as giving a more natural feel to the artificial
aspect of the source.
Five main aspects of flash systems to
consider
Power: quantity of light emitted by the
unit, referred to by its guide number. Guide number indicate its power output
in relation to a standard film speed on digital ISO setting. It’s important
when calculating flash exposure manually.
It indicate the maximum output of the flash,
with modern flash units it is possible to control output to levels below the
maximum.
Coverage: Refers to the spread of the
flash light from the point source. Ideally this should match the angle of view
of the lens used. Range are mostly between 28 and 135mm.
Recycling time: refers to the speed at
which the flash unit recharge after discharge.
Flexibility: not only its position
fixed.
Flash diffuser
over the flash head scatter emitted
light.
Flash extender
Are designed to be used with long focal length
lenses of 300 mm or longer when it’s impossible to get close enough to the
subject.
Off-camera shore cord
Acts to continue passing information
between the camera and the flash unit.
Flash bracket
Is used to support the flash unit
off-camera. Flash bracketing performs the same role as standard exposure
bracketing.
Front and back curtain
Modern camera have various settings for
flash fires at the shutter curtain opens at the beginning of the exposure, when
rear curtain sync mode is selected the flash fires at the end of the exposure. When
making long exposure and using flash creates the effect of motion blur
appearing behind the subjects.
The slow-sync flash mode
Can be used with the slow shutter speeds
to create interesting aesthetic effects.
High-speed flash-sync mode
Can be used with extremaly fast-moving
subjects to help freeze motion, when ambient light would otherwise cause an
amount of subject blur.
REFLECTOR
One of the advantages of a reflector is
that reflected light can never be more powerful than the original light.
Therefore reflected light never overpower the primary light source.
How would reflector improve the image
The result is less dramatic contrast and
softer light. The differential in light quality and intensity helps to give
form to the subject. Reflector help to add light in shadow areas.
Reflective surface should be white and
preferably uncolored, silver produce more contrast and gold more warm.
Soft box
Produce a diffused light much like
sunlight on a cloudy day, they are ideal for use in fashion and portrait.
Barn doors
Limit light spill in areas where
illumination isn’t required.
Snoot
Funnel light is typically used to
highlight key features of a subject.
NOISE/CONTRAST/MACRO/REFLECTIVE
What
causes digital noise
Digital noise is caused by the
heat generated by the sensor, which is particularly noticeable during long time
exposures as the sensor gets hotter the longer it is charged, and by he process
of amplification used to increase the light signal at higher ISO ratings. The
easiest way to avoid it is to use only low ISO ratings, less than 400, and to
maintain shutter speeds faster than 1 second.
Also enable the NR reduction noise function on the camera.
Why
is high contrast a problem
All film and digital sensors have
a limied ability to record detail in shadows and highlights simultaneously.
Take ammeter reading of the brightest par of the scene and then calculate the
exposure fot the darkest part of the scene. Work out the difference between the
two exposures in stops and this gives you your SBR. If the SBR is greater than
the latitude of the dynamic range of the sensor then the camera will be unable
to record detail in all areas of the scene and will appear as a uniform shape.
Then use a NDG filter to event the tones, and expose sacrificing deail in the
brightest or darkest tones.
How does moonlight differ from
sunlight
Moonlight is simply sunlight
reflected off the surface of the moon. The intensity of moonlight is much reduced,
compared to sunlight, in this sense, although non-diffused moonlight is
directional, I has a quality similar to that of bounced light, being softer.
This form-giving shadows with the soft quality of omni –directional light. This
light is around 18 stops dimmer than direct sunlight. Gibbous moon +1.5 stops,
quarter +3.5, crescent +6.5, new moon impractical. The colour temperature is
roughly the same as normal daylight around 5500 K.
What
is the ideal lighting for macro photography
Soft lighting from a diffused
source due to is reduced levels of contrast, which helps maintain detail in
areas of shadow and highlight simultaneously. Early mid-morning or late
afternoon are usually the ideal times of lighting. One option is to use the
flash in conjunction with a small reflector, placed directly opposite the
flash, which will act as a secondary light source of illumination. The
advantage of this set-up is that he secondary light source can never be more
powerful than the prime source, which improves the tonal quality of the
scene. Ideally single and multiple flash
units should be positioned a an angle of around 45 degrees to the subject, ans
slightly above the subject. The acute nature of this angle of light will cause
tiny shadows to form, accentuating detail and texture and adding to the overall
impression of sharpness.
How
do I cope with highly reflective surfaces.
A simple solution to avoiding hot
spots is to use a diffuser over the flash head soften the quality of light.
Can I alter the size of the light
source and quality of light
Hard light can be changed to soft
lighting by adding a diffuser o scatter the light. And soft lighting from a
large source can be made hard by reducing the size of the light source.
LOW LIGHT
The
natural light
The length of shadows decreases
as the sun rises, in the early morning shadows are long and colour temperature
alters from red to blue-white. This latter change is almos invisible to humans
because our brains perform a kind pf white balance control that ensures we see
all light as neutral white light. White balance settings, use daylightthrough
noon on a sunny day, cloudy add warmth to landscape scenes, shade when subject
is heavy shade, incandescent when tungsten light, fluorescent lighting primary
light source, flash when electrnic flash is primary light source
Pre-shadows
WB setting
When you are photographing under
a consistent light source, such as in a studio, it is possible to measure the
exact Kelvin value of the lighting and to set a specific WB to match. When shooting
outdoors under natural light, when the colour temperature of light can be
changing constantly, calculating the exact Kelvin temperature is impossible for
all practical purposes.
Fill-in flash
Fill-in flash is artificial light
to increase illumination in shadow areas, thereby reducing contrast. The
built-in pop-up flash on the camera is useful for fill-in flash but it suffers
from being positioned directly above the camera lens, which create frontal and
direct lighting. diffusing the flash will soften.
Working
in low light
Use manual exposure mode and
allow for setting slow shutter speeds via Bulb or Time setings, which enables
the shutter to be open for very long periods(minutes or even hours). To avoid
camera shake and image blur it is essential to use a tripod, keep its centre of
gravity low and avoid using the centre column, also a cable release will avoid
causing camera movement when triggering the shutter, an alternative is to use
the self-timer to trigger the shutter but this isn’t feasible when using the
Bulb/Time setting, and if the camera has it use the mirror lock-up function.
How
do I focus in low light
Most auto-focus systems in modern
cameras operate using a system known as contrast-detection. In low light
conditions contrast levels are often too low for AF to work effectively, if the
scene you are photographing contains a bright light, such as a streetlight,
that is along the same focal plane as your subject, then this can be used as
the focus point. Focus can then be lockedand the composition reframed, much as
if you were focusing on an off-centre subject. This technique can also be
applied in manual focusing mode. Another option is to use a very powerful torch
such as the IM+ candle. A third option
is to use intuitive guesswork making use of the focus distance scale on the
lens barrel and optimizing depth of field. Some professional specification
cameras have interchangeable viewing screens, enabling the standard screen to
be replaced with a special extra bright screen designed for night photography.
mardi 7 août 2012
The natural light
The
natural light
The length of shadows decreases
as the sun rises, in the early morning shadows are long and colour temperature
alters from red to blue-white. This latter change is almos invisible to humans
because our brains perform a kind pf white balance control that ensures we see
all light as neutral white light. White balance settings, use daylightthrough
noon on a sunny day, cloudy add warmth to landscape scenes, shade when subject
is heavy shade, incandescent when tungsten light, fluorescent lighting primary
light source, flash when electrnic flash is primary light source
Pre-shadows
WB setting
When you are photographing under
a consistent light source, such as in a studio, it is possible to measure the
exact Kelvin value of the lighting and to set a specific WB to match. When
shooting outdoors under natural light, when the colour temperature of light can
be changing constantly, calculating the exact Kelvin temperature is impossible
for all practical purposes.
Fill-in flash
Fill-in flash is artificial light
to increase illumination in shadow areas, thereby reducing contrast. The
built-in pop-up flash on the camera is useful for fill-in flash but it suffers
from being positioned directly above the camera lens, which create frontal and
direct lighting. diffusing the flash will soften.
Working
in low light
Use manual exposure mode and
allow for setting slow shutter speeds via Bulb or Time setings, which enables
the shutter to be open for very long periods(minutes or even hours). To avoid
camera shake and image blur it is essential to use a tripod, keep its centre of
gravity low and avoid using the centre column, also a cable release will avoid
causing camera movement when triggering the shutter, an alternative is to use
the self-timer to trigger the shutter but this isn’t feasible when using the
Bulb/Time setting, and if the camera has it use the mirror lock-up function.
How
do I focus in low light
Most auto-focus systems in modern
cameras operate using a system known as contrast-detection. In low light
conditions contrast levels are often too low for AF to work effectively, if the
scene you are photographing contains a bright light, such as a streetlight,
that is along the same focal plane as your subject, then this can be used as
the focus point. Focus can then be lockedand the composition reframed, much as
if you were focusing on an off-centre subject. This technique can also be
applied in manual focusing mode. Another option is to use a very powerful torch
such as the IM+ candle. A third option
is to use intuitive guesswork making use of the focus distance scale on the
lens barrel and optimizing depth of field. Some professional specification
cameras have interchangeable viewing screens, enabling the standard screen to
be replaced with a special extra bright screen designed for night photography.
What
causes digital noise
Digital noise is caused by the
heat generated by the sensor, which is particularly noticeable during long time
exposures as the sensor gets hotter the longer it is charged, and by he process
of amplification used to increase the light signal at higher ISO ratings. The
easiest way to avoid it is to use only low ISO ratings, less than 400, and to
maintain shutter speeds faster than 1 second.
Also enable the NR reduction noise function on the camera.
Why
is high contrast a problem
All film and digital sensors have
a limied ability to record detail in shadows and highlights simultaneously.
Take ammeter reading of the brightest par of the scene and then calculate the
exposure fot the darkest part of the scene. Work out the difference between the
two exposures in stops and this gives you your SBR. If the SBR is greater than
the latitude of the dynamic range of the sensor then the camera will be unable
to record detail in all areas of the scene and will appear as a uniform shape.
Then use a NDG filter to event the tones, and expose sacrificing deail in the
brightest or darkest tones.
How does moonlight differ from
sunlight
Moonlight is simply sunlight
reflected off the surface of the moon. The intensity of moonlight is much
reduced, compared to sunlight, in this sense, although non-diffused moonlight is
directional, I has a quality similar to that of bounced light, being softer.
This form-giving shadows with the soft quality of omni –directional light. This
light is around 18 stops dimmer than direct sunlight. Gibbous moon +1.5 stops,
quarter +3.5, crescent +6.5, new moon impractical. The colour temperature is
roughly the same as normal daylight around 5500 K.
What
is the ideal lighting for macro photography
Soft lighting from a diffused
source due to is reduced levels of contrast, which helps maintain detail in
areas of shadow and highlight simultaneously. Early mid-morning or late
afternoon are usually the ideal times of lighting. One option is to use the
flash in conjunction with a small reflector, placed directly opposite the
flash, which will act as a secondary light source of illumination. The advantage
of this set-up is that he secondary light source can never be more powerful
than the prime source, which improves the tonal quality of the scene. Ideally single and multiple flash units
should be positioned a an angle of around 45 degrees to the subject, ans
slightly above the subject. The acute nature of this angle of light will cause
tiny shadows to form, accentuating detail and texture and adding to the overall
impression of sharpness.
How
do I cope with highly reflective surfaces.
A simple solution to avoiding hot
spots is to use a diffuser over the flash head soften the quality of light.
Can I alter the size of the light
source and quality of light
Hard light can be changed to soft
lighting by adding a diffuser o scatter the light. And soft lighting from a
large source can be made hard by reducing the size of the light source.
Light&Light effect
The light
All light is formed by many
different waves but only a very few of them are visible to humans.
The ligh sprectrum:
Radio----Microwave------Infrared------Visible
light-----Ultraviolet-----x-ray-----Gamma rayor by using image processing
software.
---------long
wave length-----------------------------------------short wave
length-----------------
---------low
frequency--------------------------------------------high
frequency---------------------
---------low
energy------------------------------------------------high
energy------------------------
Ulraviolet
light can affect film and digital sensors.
Infrared
light can be used for creative photographic effects, it’s possible by fixing an
opaque filter front of Lens.
UV Filter block the uv light
which although invisible for human is
recorded by photographic colour film and less so by digital sensors. Uv light
is most prevalent at high attitude and by the coast and causes an excessive
blue colour cast.
The colour temperature varies throughout
the day from warm reds and oranges in the early morning and late afternoon
trough to cold blues around noon. Like sunrise: red, early am:red, mid am:
yellow, late am:blue, noon: clear, early pm:blue, mid pm:yellow, laepm”red,
sunset:red.
The
light effects
The intensity of light depends on
the distance between the light source and he subject and the size of the light
source. The close the light source is to the subject the greater of
illumination. A direct light source produce harder, more intense light than a
larger light source, which typically produces softer, less intense lighting.
Natural lighting is harder to
control than artificial one but you can alter the size of the light source by
using natural diffusers such as clouds or artificial diffusers. The inverse
square law is a mathematical equation to measure the effect of changing the
light to subject distance. When halving the distance between the light and the
subject the level of illumination quadruples. The quality of light refers to
how hard or soft the light is. When light is from an unobstructed point source
referred to hard lighting as it produces a greater degree of contrast and
well-defined hard-edged shadows. When the light is diffused it produce les
contrast in the scene and less well defined shadows with softer edges. The direction
from which light falls on a subject will determine where and if shadows appear.
Side lighting is less suitable for revealing detail in therefore it’s typically
used for portrait, is often considered the best direction for lighting and
should be used when you want to reveal form or depth, also it’s the best for
creating landscape images with three-dimensional appearance. .Front lighting is
more suitable when photographing a building for revealing details, for record purposes.
Backlighting will produce silhouettes exposing for the highlights or will
produce rim lighting exposing for the shadows. Backlight is ideal for creating
atmospheric images of subjects such as people, animals ,landscapes.
The light
meters and exposure
The camera has a light meter, a
through-the-lens (TTL) meter, which mesure the intensity of reflected light
entering in the lens. It is calibrated to see everything in the world as 18%
grey and will provide an exposure calculation based on the subject being 18%
grey whether it is or it isn’t. For example when photographing snow using auto exposure function it will
typically appear grey in the final
image, because the camera thinks snow is 18% grey. The manufacturer had to set
a line in the sand, so 18% - medium-tone is exactly the half way between film’s
ability to record detail in shadows and highlights. When the subject is medium-tone then the
camera will produce a technically accurate exposure. However if the subject is
lighter or darker then the camera is liable to under-expose(lighter subject) or
over-expose(darker subject) because it is always trying to archieve a
medium-tone, 18% grey result.
Film and digital sensors have
limited ability to record detail across a broad range of brightness.
------------------------------------digital
sensor
----------------------------
negative film
--------------------
positive film
The TTL light meter can be set by
measuring the level of brightness in different sections of the viewfinder
screen to assess, the multi-segment is ideal to spend little time about
exposure, the centre-weighted metering calculate an exposure value(about75%)
from the centre circle, is considered ideal for portrait when the subject fills
the centre of the frame and the background plays a less significant role in the
composition. Spot-metering mesure the intensity of light from a tiny area
usually 3-5% and is used when calculating the difference in stops between the
lightest and darkest areas of the scene, typical for landscape.
Therefore exposure compensation
can be used as snow is around two stops brighter than medium tone by applying
+2 EV(exposure value) he camera will add 2 stops extra brightness to the scene.
The
Lighting ration
refer to the level of contrast and are a
measure of the difference in stops between the brightness of the shadows areas
compared to the highlights. Ex: a model lit on her left side by a direct light
and on her right side by a soft light then the lighting ration si 2:1. This
will help to visualize exactly the strength of shadows in the final image.
dimanche 29 juillet 2012
Enhancing filters and photographic filters
It is important to take into account the
light-absorbing strength of the filters.
-Neutral
density filters (ND) are used to reduce to overall amount of light entering the
lens.
-Ultraviolet filters(UV) are used
o reduce the level of ultraviolet entering in the lens, invisible to the human
eye is recorded by film and sensors. It is strongest at high altitude and close
to the coast.
-Infrared filters are used with
specific film or with opaque filter for digital camera.
-Skylight filters are often used
in place of Uv filters, but often
produce a pink colour cast.
-Correction colour (CC), example
cyan will absorb red.
-Polarising filter, non-polarised
light which exists all around us, is what causes reflections to appaear on
shiny non-metallic surfaces such as water and glass. A polarizing filter polarizes
non-polarised light.removinf the reflection., darkens blue skies, increasing
contrast. There is circular polarizer and linear filter which will affect light
in the way but linear adversely affect the operation of auto-focus and auto-exposure
systems.
-Natural density graduate filter (NDG)half
is clear half is grey, they create an even more balance between light and dark
tones in the scene particularly where the range of tones exceeds the latitude
of the film or sensor used. The NDG hard filter and soft one, they come in
different strengths like 0.3 DNG blocks 1 stop of light to 1.2 blocks 4 stops.
A red filter absorbs blue ligh
with the effect of darkening the blue colour of the sky and increasing contrast
between dark and light tones. An orange filter has a similar effect although less
pronounced than when using red filter. Red and orange filters are less
effective on overcast days and can be too effective when used ti photograph
scenes with a predominance of other colors. For example, a scene that contains
a large area of green, a forest of trees of instance, would result in both the
sky and trees darkening if a red filter was used. However, a green filter will
lighten the leaves while still adding density to the blue sky.
-Lends hood they prevent the occurrence
of lens flare.
-Panel reflector white, silver,
gold, black positioned directly opposite the main light acting much like fill-flash u adding light to areas
of a scene unlit by the main light source.
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