Graphics Programs Reference
In-Depth Information
Lenses are rated by their maximum aperture, which is also known as lens
speed. Lenses with larger maximum aperture open up more to deliver more
light to the sensor and therefore allow faster shutter speeds, which reduce blur-
ring in low-light conditions. Faster lenses cost more than slower lenses. Prime
lenses are generally faster than zoom lenses. A fast prime lens can easily cost
more than several point-and-shoot cameras put together.
Most lenses pro-
duce their sharpest
images at their
middle apertures.
Adjusting exposure
Exposure refers to the amount of light received by the sensor. An underexposed
image didn't receive enough light and an overexposed image received too much
light (see Figure 1.12).
FIGURe 1.12
Underexposed foreground (left) and overexposed background (right)
Exposure is primarily modulated by aperture and shutter speed. All digital cam-
eras automatically choose a combination of f-stop and shutter speed in Program
mode. All but the least expensive digital cameras allow you to manually select
aperture, shutter speed, or both.
In low-light situations, natural light can be reflected onto a model (see
Figure 1.13) or supplemented by electronic flashes, which can be diffused by
studio umbrellas or portable soft boxes.
Bracketing is the practice of taking multiple shots of the same subject at dif-
ferent shutter speeds or apertures in the hope that one combination will pro-
duce the proper exposure. Most DSLR cameras have auto-bracketing features,
which allow you to rapidly expose multiple photos with varying shutter speeds
or apertures.
to play with motion
blur, try a slow shut-
ter speed, 1/30 of a
second. to freeze a
fast-moving athlete,
use a faster speed,
1/500 of a second.
