::BLewis-Photography©::
Camera Knowledge Explained.
Focal Length.
Focal length is determined by the lens you are using and is usually
defined in millimetres. It basically describes the magnification of the
lens. A focal length of 50mm is considered to be actual size (i.e. x1
magnification) and each additional 50mm of focal length increases the
magnification by 1. So 100mm = x2 magnification, 200mm = x4, 300mm = x6, 400mm = x8, etc. Obviously for bird photography large focal length lenses are the best for the job, if not essential. Unfortunately they are also the most expensive.
Shutter Speed.
Shutter speed might seem obvious and I suppose it is. It is the
amount of time that the camera exposes the film or digital sensor to the
light. Faster shutter speeds are used for moving subjects as they enable
the photographer to 'freeze' motion. As birds are very mobile fast
shutter speeds are usually essential.
ISO.
This is a numeric indication of the sensitivity to light. The higher
the number the more sensitive to light. So in dull conditions choosing a
higher ISO will give a brighter picture. However, the higher the ISO the
more grainy (or noisy) the picture is. If you are still using film, then
the ISO is determined by the film itself. If you put a 100 ISO film in
your camera then you are stuck with 100 until it is used up. With digital
you can adjust this for each shot to suit the conditions.
Depth of Field.
The depth of field describes how much of your picture is in focus. A
narrow depth of field gives your subject in sharp focus and the
background heavily blurred. A wide depth of field has both near and far
objects in focus. Depth of field is controlled by the aperture.
Aperture.
The aperture is how wide the camera opens the shutter. A larger
aperture allows more light and hence a brighter picture. It also gives a
narrower depth of field. A smaller aperture gives a darker picture but a
wider depth of field. The size of the aperture is denoted by the F
numbers. These follow an unusual pattern like 2.8,4.5, 5.6, 6.3, 7.1,
etc.. The lower the number (e.g. F2.8) the larger the aperture whilst the
larger the number (e.g. F32) the smaller the aperture. Fixed focal length
lenses have a single F number, zoom lenses with a range of F numbers (e.g.
F4-5.6). These numbers on your lens indicate the maximum aperture allowed
for that lens. Using tele-converters reduces the maximum aperture further.
Exposure.
Exposure is a term used to describe the brightness of the photograph.
Too much light and a photograph is described as over exposed. The colours
are washed out and details are lost. Too little light (more common) and
the photograph is described as under exposed. The whole picture is very
dark, may be even black, with details also lost. Under or over exposure
on film means the picture is lost as there is nothing you can do about
it. Mild under exposure with digital pictures can be corrected using
photo editing software. Over exposure is more difficult, if not impossible, to
correct. As a result many believe that it is better to slightly under
expose your digital pictures than to over expose them. However, under
exposure can create more noise (a grainy look to the picture). So
actually it's better to get your exposure correct when you take the shot.
Exposure is controlled by shutter speed, aperture and ISO.
Metering.
Modern cameras use metering to determine exposure. The camera samples
the light, dark and mid-tones of the subject and determines the settings
to 'correctly' expose the picture. If you are using your camera in full
automatic mode, this will include aperture and shutter speed. If you set
the shutter speed manually, it works out the 'correct' aperture. If you
set the aperture manually, it works out the 'correct' shutter speed. If
you are in full manual mode, setting shutter speed and aperture yourself,
it obviously does nothing. Now I've put the word 'correct' in inverted
commas for a reason. In most cases where the image is a mixture of light, dark
and mid-tones, it probably will get it correct. However, if the image is
mostly dark (e.g. a black bird on a dark background) it will over-expose
the picture. If it is mostly light (e.g. a white bird on a light
background) it will under-expose the picture. So some manual correction
will be needed. There are different modes of metering. Evaluative
metering (sometimes known as matrix metering) is where the whole image in
view is divided into zones. The camera works out what the main subject
is, how it is lit, what the background light is like and works out the best
aperture and/or shutter speed to expose the image. Partial or spot
metering is where only a small area at the centre of the image in view is
used to calculate what aperture and/or shutter speed to use. Centre
weighted metering is where the whole image in view is analysed but
greater emphasis is given to the centre of the image when calculating the
aperture and/or shutter speed to use. This is normally the default mode on most
cameras.
White Balance.
Light consists of three primary colours, red, blue and green. Some
light sources have these colours in different strengths (unbalanced).
Although our eye is pretty good at compensating for this, in your
photographs it can give your subject an appearance of unnatural colours.
White balance can be adjusted on many SLR cameras allowing you to correct
this if you are experienced enough to know how to get it right
are using digital cameras you can adjust this later with photo editing software
if you need to, which is possible to do if you take RAW format pictures.