Basic photography... Worth for you to take a look
Too often, we forget that new Digital Single Lens Reflex (DSLR) cameras are sold every day to someone with
no experience with DSLR cameras at all. Whoever we are and however good we are, we started somewhere. So I
decided to dedicate the next few posts to the "Newbies", the entry-lever photographers, the shooters upgrading
from a point-and-shoot camera, etc. Let's go back to the basics of photography.
This post will not make you an expert in photography alone. Like any other skill we learn, practice is what
makes us excel in any of our undertakings. There are many books on photo techniques on the market that you
can get to further learn the craft or art of photography. For years, Kodak has regularly publish updated books
targeted to beginners all the way on up to the professional photographers. Of course, lots of information is
also available on the internet.
Photography, is about light. It’s about light reaching a media, film or digital sensor, and turning the results into an
image that we can see, on a computer screen for example, or print on paper.
Other than the lighting conditions of a scene, there are three major items that directly affect how the light
reaches the recording media. The Aperture (lens opening), the shutter speed (the speed at which the shutter
opens and closes) and the media sensitivity also known as ISO number (the amount of light recording on the media
for a given exposure). Too much light reaching the media, and the image will be washed out. Too little light
reaching the media, and the image will be too dark. This is to say that the balance between these three items must
be just right. Technically speaking, a large aperture will let a lot of light in, and therefore the shutter speed
and/or the recording media will need to be adjusted accordingly. Let’s assume for a moment that the sensitivity
is set at ISO 200 and cannot be changed. We now have to balance the aperture and shutter speed to get the correct
amount of light in. An aperture of f/4 at a shutter speed of 1/125th of a second would give the same results as
an aperture of f/5.6 at a shutter speed of 1/60th of a second. In other words, if you increase the aperture by
one F-stop and decrease the shutter speed by one shutter step, the same amount of light would would reach the
film or sensor. The difference between the two is the composition. Since we are dealing with digital single lens
reflex (DSLR) cameras, from now on lets use the word “sensor” for media.
Aperture scale explained
The aperture, being the lens diaghphram opening, lets more or less light pass through the lens. The f-number
(aperture opening) is proportional to the ratio between the lens focal length and aperture diameter, which is
proportional to the square root of the aperture area. Big analogy but what does all that means? Well, lenses
are usually marked with the F-numbers ranging from the largest aperture to the smallest aperture. For example,
a typical lens could have an aperture range of f/2.8 to f/16. The lens would be marked as follow : f/ 16, f/11,
f/8, f/5.6, f/4, f/2.8. In this example, the largest aperture would be f/2.8 while the smallest would be f/16.
Have you noticed something a little surprising here? The larger the number is, the smaller the aperture is. You
need to remember that. Furthermore, each (f-stop) number to the right lets twice the amount of light in as the
(f-stop) number to its left and each (f-stop) number to the left lets half the light in as the (f-stop) number
to its right. For example, f/4 lets twice as much light in as f/5.6 but only one half the light of f/2.8, and
so on. One unit of increment in aperture is called a stop.
Shutter Speed scale explained
In photography, shutter speed is the length of time the shutter takes to open and close. The total exposure is
proportional to the duration of lighr reaching the imaage sensor. Similarly to the aperture, a standardized 2:1
scale was adopted for shutter speed so that opening one aperture f-stop and reducing the shutter speed by one
step resulted in the identical exposure. The agreed standards for shutter speeds are typically 1 sec,1/2 sec,
1/4 sec, 1/8 sec, 1/15 sec, 1/30 sec, 1/60 sec, 1/125 sec, 1/250 sec, 1/500 ses, 1/1000 sec, etc. A shutter
speed of 1/125 sec lets twice as much light in as a shutter speed of 1/250 sec, but half the light of a shutter
speed of 1/60 sec. For example, combining aperture and shutter speed, a shutter speed of 1/125 sec with an
aperture of f/16 is equivalent to a shutter speed of 1/250 sec and an aperture of f/8. Alternatively, a shutter
speed of 1/125 sec with an aperture of f/16 is also equivalent to a shutter speed of 1/60 sec with an aperture
of f/22. Remember that one unit of increment in shutter speed is called a step.
ISO Value scale explained
Similarly to the aperture and shutter speed, the ISO linear scale, which corresponds to the older ASA scale,
is 2:1. Doubling the speed of a film implies doubling the numeric value that designates the film speed. Here
again, a film rated at 200 ASA or ISO 200 will absorb half of the light of a 400 ASA or ISO 400 film, but
twice as much light of a 100 ASA or ISO 100 film. In the digital world, the sensitivity defines ISO speed
in terms of the amount of light needed to achieve a certain quality in the sense of a per-pixel signal-to-noise
ratio. The image sensors in digital cameras can be adjusted, or can have their outputs adjusted, in sensitivity
to function with metering at any given comparative ISO setting. This is usually done by simply amplifying the
output of the image sensor, which increases image noise, sometimes beyond the level that the ISO standard says
is acceptable. Just as with photographic film, greater sensitivity comes with some loss of image quality,
visible as image noise. What does that mean for you? The lower the ISO value on your digital camera, the
less noise you will have and therefore, your image will appear clearer. ISO 200 is twice as sensitive to
light as ISO 100 but half of ISO 400
You can understand that to take a properly exposed photograph, one has to balance the aperture and shutter
speed according to a sensitivity value (ISO). In the 35mm film era, the sensitivity would remain constant
for the duration of the roll of film. In digital, the sensitivity (ISO) can be adjusted on the fly, making
this third element more important and flexible than ever. Luckily, technology spares us from long exposure
calculations. We can adjust one of these three elements, and the camera will adjust the two other automatically.
We can set the Aperture, for example, and let the camera select the appropriate shutter speed. That is called
Aperture Priority, (Av or Aperture value) on your camera mode dial. If the exposure is impossible at the chosen
aperture, the camera will either suggest using the flash or increasing the ISO rating. Both of these functions
can be set to make the decision automatically or within some preset parameters. Alternatively, you can decide
to set the shutter speed and the camera will choose the appropriate aperture. That is called Shutter Priority
(Tv or Time value) on your mode dial
Your camera has many preset and automatic modes, represented by small icons on the mode dial. This further
simplifies the decision making for the photographer. You set the camera to portrait, and the camera is already
programmed to use the standard settings typical for a portrait shot. You set it to moving objects, and the camera leans toward a fast
shutter speed to freeze the action. You set it to landscape and the camera leans toward a small aperture for
maximum depth of field. These settings are fine for the casual photographers and at the beginning of your
learning curve as photographer, but sooner or later, you will want to have more control over the camera.
Although the technical progress made in just the last decade is nothing short of astonishing, the human element
is still far superior in decision making. Once you fully understand the three essentials items explained in the
preceding post, you will take the creativity control over the camera.
Adjustments to consider
Choosing a small aperture can make the scene in focus from just a few feet or inches in front of the camera to
infinity.It is very useful in landscape photography. This effect is proportionally accentuated when using wide
angle lenses. However it will require a slower speed or a faster ISO. Tripods are commonly used in landscape
photography.
Choosing a large aperture limits the depth of field, making your subject stand out with a blurry background and
foreground. (It's really called selective focusing) It will likely require a fast shutter speed or lower ISO
value. (P.S. Always try to shoot at the lowest ISO value as possible. It will always produce the minimum amount
of noise) This is very useful for portraits. This depth of field is proportionally accentuated with telephoto
lenses. However, with telephotos, it will probably require a faster shutter speed (because a telephoto that
brings the subject say, five times closer, will also register the movements as being five time faster) or a
higher ISO value, as the maximum permitted aperture will be smaller
Using a fast shutter speed can freeze the action and is often used for sports and fast moving activities.
However, it will require a wider aperture, a faster ISO value or the use of a flash.
Using a slow shutter speed will allow taking pictures at night or will render a feeling of movement by
deliberately blurring a moving area of a scene such as water falls, etc. You will likely need a tripod and
perhaps a wider aperture and faster ISO.
You can shoot with a very fast ISO and capture almost any image with little effort, but the image will contain
noise.
You must have realized by now that photography is indeed all about light. Modern DSLRs have other tools to
further refine the art of capturing the images with the optimum results. Built-in meters give you the choices
between multi-segments metering, center-weighted or spot metering. Auto focus modes in either single or
continuous focus make your photos crystal clear and sharp despite you. Shake reduction allows using slower speed
than most humans could ever achieve by hand-holding the camera. White balance control assures, most of the times
anyway, that the color of the scene will be the same on the saved image or file. Instant view of the capture
images allows you to retake the shot(s) if not satisfied. The use of memory cards allows you to take hundreds or
even thousands of shots, at practically no cost other than the purchasing cost of the card. I tell you, with
digital cameras, especially with Pentax DSLRs, we’ve got it made. Remember what they say;
“practice makes perfect” or close to it anyway as I don’t believe that perfection can ever be achieved.
[ 本帖最后由 PentaxYong 于 11-3-2008 08:34 PM 编辑 ]
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