Bernie's Better Beginner's Guide to Photography for Computer
Geeks Who Want to be Digital Artists
Illustrated with photos wot I 'ave taken.
This is a beginner's guide for computer geeks who want to be
digital artists. Specifically:
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Roll over a section of the diagram.
You are a beginner: you
have little experience with photography beyond point-and-shoot
cameras and mobile phones. If you are not a beginner then why are
you reading this? Shoo! Go outside and play with your camera.
You want to be a digital artist: you intend to make a small
number of photos or illustrations that are as close to perfection
as you can get them.
If you want to take large numbers of shots to document weddings
or sports events for example, then you won't want to edit them all
on a computer afterwards so you have to get everything perfect when
you take the shot, just like in ye olden days of film photography.
This guide may well help you, but ignore the section on digital
manipulation. Then practice. A lot.
On the other hand if you don't care about making each shot
perfect then save yourself a lot of money and buy a point-and-shoot
camera.
You have a computer and
know how to use it. If you are reading this, I'm guessing that you
do. If you are not reading this then something very strange is
happening right now.
You are a geek: The fact that
you're reading this article already gave you a 90% chance of being
a geek, and taking the time to roll over all these little bits
guarantees it. If you think Venn diagrams are interesting, you're a
geek, end of story. I like to define a geek as someone who cares
enough about something that they want to get good at it for their
own sake, not to impress others or earn more (though being a geek
helps you with those two goals too).
Moot point – all
digital artists are computer geeks
You are a computer
geek: you enjoy using computers and can learn a piece of software
by playing with it for a day or two. If you are not a computer geek
then it may be for the best to use a digital camera as if it was a
film camera: forget digital retouching and just capture the best
image you can when you shoot. This article will still be useful,
but ignore the section on digital manipulation.
If all of the above apply, come
on in!
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There is a lot of material in this article, so I suggest you
have your camera with you as you read it and try out the techniques
as you go along. If you don't have a camera yet then you can still
enjoy this article; however if you do intend to buy a camera sooner
or later, I suggest doing so before you read. Check out the
buying advice at the end of the page.
This is the first in a series of articles on photography. If you
like what you see, why not subscribe to my RSS
feed for photography articles. I welcome any feedback,
post a comment to my blog.
Introduction
An extended apology: Most authors of
photography guides are experienced professionals, and speak with
the authority of the published photographer. Instead I write this
beginner's guide with the authority of a beginner. I flatter myself
that I am better placed to advise the beginner geek on how to learn
to use a camera than the professional photographer is: I have just
been a beginner myself, so what was confusing and what was simple
is fresh in my mind.
Speaking of my being a beginner, this is the first long article
I've written. Do e-mail me and tell me what you think of it. bernie
at berniecode dot com.
</apology>
This is the guide I wish someone had written for me when I
started 3 months ago. It's much shorter than photography books that
cover the same topics because it's a computer geek's guide. I skip
right over the basics of using a camera because you can guess your
way through the basics or even read your camera manual (wimp!). I
skip any advice about composition or artistic technique because
there are better guides that cover those (though I might give it a
shot next month). I use terms without defining them because I
assume you can use Wikipedia if you need more detail.
For further reading covering field technique and composition I
unreservedly recommend John Shaw's Nature Photography Field Guide.
Also, the National Geographic field guides are said (by my sister)
to be good.
If you want to be a digital artist then you'll need to be so
comfortable using your camera that the exposure controls are second
nature to you, so you can focus yourself on composing the scene
that you want. This guide tries to get you to that point as quickly
as possible. Some otherwise excellent photography guides take ages
walking through the basics of exposure before gradually eking out
the advanced details. This will never do: you're a geek and can be
dropped in at the deep end.
This guide doesn't even try and address how to create a
composition that qualifies as art, but
this one does, and the book
Photography and the Art of Seeing goes further.
Onwards…
Digital SLR systems
For this article I'll be assuming that you have an SLR camera*.
The distinguishing feature of an SLR is that when you look through
the viewfinder you see through the lens. This means that you can
view the picture pretty much exactly as it will look when you take
it. You can also change the lens mounted on the camera body to
alter the look of the photo. The technical details are quite
interesting, but you don't need to know them to use the
camera.
When you take a picture with a digital SLR you allow an amount
of light through a lens, focusing it onto a bit of
silicon called a image sensor that contains
light-sensitive cells that record an image.
The amount of light that you allow in is called the
exposure. Getting the correct exposure is most of
the effort of learning photography, and hence the main thrust of
this article. Playing with creative effects like long exposure is
much easier once you have exposure down to second nature.
Focal length
Focal length is the most obvious way in which a lens affects a
photo: it controls the angle of view, and hence how much of the
scene is included in your photo. The reason that it is measured in
focal length rather than degrees, is that the angle of view yielded
by a certain focal length depends on the size of the camera's image
sensor. This relationship is easy to see in a diagram of a pinhole camera,
where the focal length is the same as the distance between the
pinhole and the film:
With a drum roll to celebrate the first time in my life that
trigonometry has had any practical purpose, the angle of view is
given by the formula arctan((<sensor size>/2) /
<focal length>) x 2, for reasons that should become
obvious if you split the diagram above into right-angled
triangles.
If you don't fancy carrying a calculator, you can visualise how
focal length will affect the angle of view by imagining looking
through a piece of card with a 35mm wide rectangular hole in it:
hold the card twice as far from your face and you'll see half as
much through it.
So doubling the focal length is just like cropping the
photo to half of its width and height and blowing up the
result to full size, except without the loss of resolution that
would occur if you did that in Photoshop. Everything else about
the picture remains exactly the same.
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A landscape at 18mm, the white box marking 1/5 of
the width and height
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The same landscape at 90mm: the focal length is 5
times longer so the area marked by the white box fills the whole
scene
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Focal length and perspective: OK, backpedaling
time. If two photos are taken from the same position at
different focal lengths, then the longer focal length photo will
look like a crop from the middle of the shorter focal length photo.
However, often a photographer will change position as she changes
focal length. When you're shooting a specific subject you will use
a wide angle lens and get right up close to the subject, or a
telephoto lens and stand back; either way, the subject fills the
whole frame, but the perspective will look very different:
Using a wide angle lens means that the camera is much closer to
the subject than the subject is to the background. This exaggerates
perspective and makes the background seem small and distant. The
reverse is true with the telephoto shot, which includes less of the
background while making it appear closer to the subject. This
thistle was shot with 3 different focal lengths:
Stops and exposure settings: the basics
When you take a picture you allow an amount of light through the
lens, focusing it onto the image sensor. The amount of light you
let in is measured in stops. Stops are a relative
measure of lightness: adding one stop means doubling of the amount
of light that the plate records. We measure light like this because
the human eye perceives each doubling to be an equal increase in
light. On old cameras, stops were literally dents in a dial that
made it easy to stop when you reached the desired setting.
Using a relative measure makes sense because there is no such
thing as a standard amount of light that equals grey. How bright
grey is depends on how strongly lit the scene is; a dark granite
rock in bright sunshine actually has more light reflecting off it
than than snow at twilight. It is not the absolute brightness of
objects in your scene that matters, but their brightness relative
to each other, or how many stops apart they are. When photographing
these objects you adjust the exposure settings to make sure that
the twilight snow still looks white and the sunlit rock looks
dark.
The amount of light you record is controlled by the camera's
exposure settings: aperture, shutter speed and
sensitivity. Opening the aperture by a stop or decreasing
the shutter speed by a stop or increasing the sensitivity by a stop
all have the effect of doubling the brightness of your scene.
However, the shutter speed and aperture have other aesthetic
effects that affect how your picture looks in a way that is very
hard to remove or replicate in Photoshop, so you must make a
decision when you shoot.
Shutter speed
The shutter speed is considered an exposure setting because
opening the shutter for twice as long lets in twice as much light
which increases the exposure of the whole scene by a stop. However
you can also use it aesthetically: faster shutter speeds freeze a
moving subject, slower speeds record a motion blur. Neither is
'correct': a photo of a stream with a 1/800 second shutter would
record each sharp sparkling droplet of water frozen in mid-air,
whereas a 4 second exposure would render the stream as a softly
flowing ethereal smoke. Either can look beautiful.
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A shutter speed of 1/800 second freezes this
baseball in mid-air.
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A 10 second exposure produces streaked lines of
headlights and a ghost of a car that was parked for half of the
exposure.
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Aperture, or 1, 1.4, 2, 2.8, 4, 5.6, 8, erm, what the
f***?
Lenses have an aperture to control the amount of light entering
them. This is an iris that can open and close to allow more or less
light in. Aperture is measured in 'f numbers' – written f/x where x
is the ratio of the aperture width to the focal
length. Low f-numbers mean wide apertures letting in more
light. Aperture has a reputation for being complicated so some
guides suggest that you just memorize the f-number sequence and
ignore the internal details. Being a geek, you'll find it much
simpler when you understand why it is measured like this.
The first supposedly confusing thing about aperture is that it
is not measured as a width but as a ratio of focal length to width.
This makes more sense if you consider that the scene you're
photographing is a light source. Recall that doubling the focal
length will half the width and height of the bit of the scene that
you project onto the camera plate. Therefore at double the focal
length, only 1/4 of the scene area is providing light, so the
aperture area must be 4 times as large to compensate (i.e. the
aperture width must double). A constant f-number means a
constant amount of light entering the aperture regardless
of the focal length.
The next supposedly confusing thing about aperture is that the
f-number sequence goes in stop increments: 1, 1.4, 2, 2.8, 4, 5.6,
8, 11, 16, 22, 32. There is a logic to this. A 50mm lens with a
50mm aperture will have an f-number of f/1 (the ratio of the focal
length to the aperture diameter: 50/50 = 1). If you want to halve
the amount of light reaching the sensor you must halve the area of
the aperture. To half the area of a circle you divide the diameter
by 1.4 (give or take), and since diameter is the denominator in the
f-number equation, this means that the f-number is increased by a
factor of 1.4. Each f-number is 1.4 times the previous one
and lets in half as much light. When someone says "close",
"reduce" or "step down" the aperture, they mean increase
the f-number.
Like shutter speed, aperture affects the look of the photo,
specifically the depth of field. At narrow
apertures the whole of a scene will be in focus, whereas at wide
apertures only the bit of the scene that you focus on will be on
focus; as is clear in the case of these cheap fake flowers:
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At f/16 the background is distracting
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At f/1.4 the background is reduced to a blur, but
not all of the subject is in focus either.
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The nature of the out-of-focus blur that an aperture produces is
called bokeh, a term coined by a magazine editor
sick of hearing people mispronounce the Japanese word 'boke'
(meaning blur) to rhyme with smoke. Good on him, but I'm still not
sure how I'm supposed to pronounce it.
Long focal lengths and bokeh: Using a long
focal length lens appears to make the background more blurred. In
fact the background is just as blurred, but is larger. This is
easier to see in a photo that only contains the out of focus
background:
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A blurred leafy background at 30mm, f/2.8
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The same shot at 85mm, f/2.8.
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In both shots each leaf is just as blurred relative to its own
size, but in the wide angle there are more leaves and each one is
smaller. In either shot you would reposition the camera so that the
subject filled the whole frame. The long focal length therefore
increases the size of the background relative to the subject,
increasing the apparent blur. This is useful in portraits, when
background detail only serves to distract from your subject.
Sensitivity
The sensitivity of the camera's plate is measured in ISO
sensitivity units which were originally used to measure
the sensitivity of chemical film. Most digital SLRs offer a range
from 100 to 1600, with 100 being the least sensitive. Some offer
lower or higher ISOs; as of September 2007 the champion is the
£3,400 Nikon D3 with a maximum ISO setting of 25,600.
Sensitivity is a very useful exposure setting, because it
(almost) doesn't affect the look of the final image, so can be used
to help you achieve a combination of aperture and shutter speed
that gives you the look you need. Take this shot for example:
The extreme depth of field required a narrow aperture of f/22,
ensuring that the grass and mountains were sharp, and my camera's
meter decided that a shutter speed of 1/15 second was required to
correctly expose the image. A breeze was causing the grass to sway
so much that a shutter speed of 1/60 was required to freeze it.
1/60 is 4 times faster than 1/15, so the scene would be
underexposed by 2 stops. I increased the sensitivity by 2 stops
from 100 to 400 and the scene was correctly exposed.
There is a caveat: noise. At very high sensitivities the
picture becomes noisy. This is because at higher ISOs you
are making an image from a smaller amount of light, so the signal
to noise ratio drops. As a last resort you can try to remove this
noise in Photoshop, but this can also remove fine detail so it is
better to get a clean photo in the first place.
The following set of magnified images show individual pixels
from a photo of a lamp fitting at various ISOs. These results will
hold true for most digital SLRs. However, top of the line
professional models will have lower noise at high ISOs.
At ISO 100, no noise is visible |
At ISO 400 the picture is still excellent |
At ISO 800, noise becomes visible |
At ISO 1600 the image is very noisy |
However, noise is less obvious in print than it is on screen, so
you may well be able to get away with high sensitivities.
As a rule of thumb you should shoot in the lowest ISO
that gives you the shutter speed and depth of field that you
need. If you need more depth of field but don't want to
reduce the shutter speed, increase the ISO and reduce the aperture.
If you need a faster shutter speed and don't want to lose depth of
field by opening up the aperture, increase the ISO and the shutter
speed. If you're shooting a still landscape on a tripod at ISO 800
and 1/100 second shutter speed, you're just wasting image quality:
reduce the ISO to 100 and the shutter speed to 1/12 second. Some
SLRs and most Point and Shoot cameras have an Auto
ISO setting, which selects the lowest ISO that will give
you a reasonable shutter speed. What qualifies as "reasonable" is
an exercise left to the manufacturer, so you may still need to set
the ISO manually if your camera's choice isn't appropriate.
I find that far more of my shots are ruined by motion blur
caused by slow shutter speeds than by noise so don't
hesitate to crank up the sensitivity if you need to. In
addition, it is often possible to remove much of the noise on in
processing. The following crop is from a picture that had to be
taken at my camera's highest sensitivity. The top half is processed
with the Photoshop plugin Noise Ninja.
Metering
Digital SLRs have built-in light meters that calculate the
required exposure settings to expose the object you're pointing the
camera at as a medium tone. However, the camera doesn't know what
you're pointing at, and will happily expose a white subject as grey
unless you correct the exposure settings. You use the
exposure dial to tell the camera to render the
object that you are pointing at as a lighter or darker tone.
There are 5 stops between black and white, so black is 2.5 stops
below mid-toned and white is 2.5 stops above mid-toned (take this
as read for now, I cover it in more detail in the next section).
Strangely, my Canon 30D's exposure dial only covers 2 stops, so I
have to use manual mode if I need absolute whites or blacks.
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The dial at the default setting: the metered
object will be mid-toned.
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The metered object will be near-white.
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The metered object will be near-black.
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You can set your camera to spot metering which
meters a small area in the centre of the scene,
centre-weighted metering which meters the whole
scene but pays more attention to the middle, or evaluative
metering which meters the whole scene. Especially for
evaluative metering, check the histogram (see the next section)
right after shooting to make sure that the exposure came out
correctly.
The metering lock button lets you meter a
specific object, lock the exposure settings for that meter reading,
and then point the camera somewhere else to take the picture. This
is how you meter an object that is not right in the middle of your
composition.
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This waterfall looked white, so I spot-metered it
and dialed in 2 stops of overexposure to make sure that it looked
like it appeared in real life.
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You can also change the suggested exposure values
for creative effect. This moody nebulous image was actually a
bright cloudy sky. I metered the cloud at the bottom, used the
metering lock button to record that reading, then dialed in 2 stops
of underexposure to render it near-black.
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Digital SLRs have four useful exposure modes that work with
metering. Program mode chooses an aperture and
shutter speed for you, leaving you free to think about composition.
Aperture priority mode lets you choose an
aperture, and the camera will set the shutter speed to correctly
expose the scene; this is the most useful mode because it makes it
easy to get the best depth of field possible (set to minimum
aperture) or the fastest available shutter speed for the current
lighting (set to maximum aperture). Shutter priority
mode lets you pick a shutter speed and the camera will set
the aperture. In all of these automatic modes, you point the camera
at an object and then use the exposure dial to tell the camera how
light or dark that object should be.
In manual mode the exposure dial works the
other way round: you choose an aperture and shutter speed, and the
metering system will set the exposure dial to tell you how light or
dark the object you're pointing at is:
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The exposure dial indicating that with the
current settings, the metered object will be 2/3 of a stop above
mid-toned.
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When I'm taking time to work a subject, carefully setting up
shots with specific effects in mind, I like to use manual mode
since it forces me to think about the exposure settings. When I'm
walking around looking for interesting moments to take snap shots
of, I stick to the automatic modes.
Histograms
Digital SLRs come with a histogram display so that you can tell
how an image is exposed. Set your camera to show you an RGB
histogram of each shot after you take it so you can tell if it is
correctly exposed and retake the shot if necessary. Later in this
guide I show you how to correct a poor exposure on a computer, but
you'll get better results and a smug feeling of
competency if you get it right in the field.
Incorrectly exposed images produce histograms with large spikes
at either end; correctly exposed images look like smooth bell
curves. There is an example of each in the next section.
Looking at the histogram after each shot is the fastest way to
get a feel for correct exposure.
Stops and exposure: advanced stuff
Every device for capturing light has a dynamic
range – the number of stops between the darkest black and
the lightest white that can be captured. Shades outside this range
will be clipped, appearing featureless black or white. This is why,
when somebody shines a torch at you at night, you can't see their
face – the human eye can perceive 15 stops of dynamic range, and
the torch bulb is more than 15 stops lighter than their face.
On a film camera there are 5 stops between the darkest black and
the lightest white. This is a much smaller dynamic range than the
human eye can detect. This means that if you have a scene with say
a bright cloudy sky and a dark shaded valley, you can see both in
detail at the same time but a camera can not. If the shadows in the
valley are more than 5 stops darker than the white of the clouds,
then either the clouds will be a wash of overexposed white or the
shadows will be a mass of underexposed black.
Digital SLR camera sensors actually capture much more
information that just the 5 stops that you see on your screen. My
Canon 30D captures 9 stops in total: 2 stops on each side of the 5
stops you can see. It uses this information internally to adjust
white balance, but in order to reproduce the rich,
high-contrast look of traditional film the 9 stops are clipped down
to 5 to produce a JPEG file that looks like a traditional film
print.
Traditional film photographers got around the 5-stop limit by
using graduated neutral density filters – attachments for the front
of a lens that shaded the sky, decreasing its brightness so that
the sky and shadows could both be properly exposed. Don't bother:
the digital artist has two tools not available to the film
photographer that are far more flexible. By using RAW image
adjustment and combining multiple shots
in Photoshop, you can create your perfect exposure back in the
office, leaving you free in the field to focus on choices that
can't be changed later like motion blur and depth of field.
RAW image adjustment
Digital cameras actually capture 9 stops of dynamic range and
then clip it down to 5 stops when the image is converted to JPEG.
However, if you set your camera to shoot in RAW, all the clipped
information will be saved so you can change your mind about how you
want it to be clipped later.
Here's an example of a tree that I shot against a bright sky on
a sunny day:
The camera's automatic metering set the aperture to f/10 and
shutter speed to 1/250 second which recorded the sky correctly as a
light blue with bright white clouds. However when I looked at the
scene in person the tree was a brilliantly backlit bright green,
but here it is a dark silhouette – around 2 stops too dark compared
to how my eyes saw it. This histogram of all individual red, green
and blue pixel values shows the problem clearly; the spike to the
left is caused by all the detail darker than the lowest of the 5
stops being clipped to plain black:
If I manually increased the exposure of the whole scene by 2
stops, say by decreasing the shutter speed to 1/60, the sky would
have lost all detail and become a wash of white. The solution is to
use a RAW adjustment program to selectively lighten the
underexposed shadows without lightening the correctly exposed
highlights. Your camera should come with a program that does this,
but if Canon's program is anything to go by it won't be nearly as
usable as Photoshop's RAW file import dialogue. Canon's program is
said to produce a higher image quality; personally I can't tell the
difference.
Photoshop gives you a 'Fill light' slider that increases the
brightness of the shadows selectively:
And as you can see from the new histogram, the spike at the left
is gone and replaced with a nice smooth bell curve:
Of course there is a cost – loss of contrast in
the highlights, which had to be compressed to make room for the
shadow detail. Compare the second histogram to the first. The three
peaks for red green and blue to the right of the graph correspond
the gradient across the sky. They exist in both histograms, but in
the second one they are narrower: the difference between the
lightest and darkest bit of sky is smaller than in the first
exposure, and hence the gradient across the sky is less dramatic.
In this case, the trade-off is easily worthwhile.
Combining multiple shots
RAW image adjustment works well when you have no more than a
couple of stops underexposure or overexposure, because if you go
more than 2 stops past the 5 stop limit of a scene's dynamic range,
you exceed the 9 stop dynamic range of your camera's sensor and any
detail in the poorly exposed areas is lost for ever.
Outside the window of my Norwegian holiday cabin where my wife
is sunbathing it is a bright day; inside where I am hunched over a
laptop it is much darker:
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In order to get a good exposure of the inside, I
needed a shutter speed of 1/3 second at f/4
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Exposing the outside correctly required 1/80
second at the same aperture
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This 5 stop difference is far more than we can hope to recover
with RAW image adjustment. If you shoot both exposures, you can
combine them in Photoshop using a layer mask to create an image
that would be impossible using a film camera:
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Using a mask used to combine the 2 exposures
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... in Photoshop ...
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... Yields an image that looks more like what my
eyes saw at the time.
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I created the layer mask by inverting the dark image, blurring
it, increasing the contrast and retouching a few areas with the
brush tool.
Make sure you shoot with a tripod so that the
two exposures overlay accurately (unlike in my hurried attempt,
where blurring from hand-holding shows up in the interior shot and
rotating / resizing was necessary to realign the images). Then take
both photos into Photoshop as layers, add a layer mask, and use the
brush tool on the layer mask to literally paint detail into the
shadows. It's surprising how well it works.
White balance
Artificial light is much warmer than sunlight, with more red and
less blue in it. Your eyes adjust to the current light temperature
and after a while you won't notice it. Cameras do not automatically
adjust however:
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This portrait was taken under dim street
lighting, rendering it unusable without correction.
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Adjusting the white balance to the lowest
temperature that Photoshop's RAW import dialogue supports was
enough to correct this extreme lighting.
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Cameras have a setting to correct white balance as you take the
shot, but I find it easier to leave the camera alone and correct
the white balance on my computer.
For a detailed technical explanation of what's actually
happening, check out this article: Understanding
White Balance.