Introduction
to Photography
Part 4
The Histogram.
The histogram is simply a chart
that shows the distribution of values of something. In digital
photography, that something is usually brightness, but often
saturation. The histogram shows you graphically how much of your
image contains shadows or middle tones or highlights.
Common Lens Problems.
Lens Diffraction:
If your using good technique and
your images are still losing important detail, it may be due to lens
diffraction. It's basically caused be using very small apertures to
gain a greater depth of field, but can result in softening and loss
of definition.
The solution is pretty simple; Avoid
using the highest (F)
number on the lens where possible.
Vignetting:
The characteristic of this effect
is a darkening of the corners of the frame, where the lens is
actually capturing its own sides. It's particularly noticeable when
you're shooting a clear sky. The problem is something regularly
associated with Wide-Angle lens, although it only becomes a major
concern when you're shooting on a Full-Frame camera, which makes use
of the full diameter of the lens. Vignetting can be a positive,
creative tool as well; helping to drew attention to the center of the frame.
If
you notice this effect try zooming in a touch. Alternatively,
Photoshop lens correction tools do an excellent job correcting this situation.
Barrel Distortion:
Pictures look like they've been
wrapped around a barrel, with the central areas far larger than they
should be.
Rather than standing close and zooming
out, step back and zoom in.
Converging Verticals:
You'll usually see this when your
shooting architecture from ground level with standard to Wide-Angle
lenses. By tilting the lens up, you'll see a distortion of
perspective, with the base of buildings seemingly wider than the tops.
If
you don't like the effect, either hire or buy a dedicated, expensive
tilt and shift lens, which removes this effect, or use a perspective
tweak in Photoshop after the shot.
Lens Flare:
Include a bright light source in
the frame or allow stray light to glance across the front element and
you'll end up with pictures that have a ghostly, contras reducing
sheen across them. You may also notice polygonal bright spots through
the viewfinder, which can be distracting in the final shot.
The answer is to keep the front element
spotless and fit a lens hood. If you don't have one, or it's not deep
enough to be effective, hold you hand or a piece of card out of shot
just above the end of the lens to shield it.
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