Quality
The quality of a lens is a huge factor in the
quality of an image, cheaper lenses will tend to have more
artifacts and distortion than higher end ones. In
photography the more you
spend on a lens the better off you are, the pricier
lenses tend to have higher quality glass and
electronic components in them than the more entry
level ones. They also tend to do a better job at
correcting chromatic aberration and image focusing
than their lower end counterparts.
Chromatic Aberration
Directly tied to the quality of the lens is the
degree of chromatic aberration that appears in the
final image. Chromatic aberration, or “color
fringing” is the result of the lens focusing
different colors of light on different points of the
sensor due to the refractive properties of
individual wavelengths of light (Bockaert). Higher
end SLR lens’ will correct this effect by having
sets of lenses inside the housing that correct for this
effect by “catching” the light rays and refocusing
them on the camera sensor.
Left image shows
chromatic aberration, right image shows how higher
end lenses correct it. Images credit:
http://www.dpreview.com/learn/?/Glossary/Optical/chromatic_aberration_01.htm
Focal Points
The focal point of a camera is a very important
aspect to take into consideration when selecting
camera lenses. The focal length for a camera lens is
the distance away from the center of the glass lens
that the light rays will be focused on. The shorter
the focal length of the unit the closer to your
subject you need to be; this works for long range
lenses too, the farther away the subject that you
want to photograph is the longer the focal length of
your lens. One of Canon’s high end lenses has a
minimum focus distance of 19 feet,
anything closer than that will be out of focus and
blurry; and one by Sigma has one of only 4mm.
Aperture
Another important piece of DSLR lens is the aperture
mechanism. This piece of the camera adjusts the
depth of field of the lens. The size of the aperture
is measured in a unit-less number called f-stops,
the higher the f-stop number the smaller the
opening. The depth of field of the camera is
adjusted according to the f-stop that the camera is
set at; a small opening increases the distance that
an object can be in focus at and a large opening
decreases it (leofoo).
Two different aperture settings,
left image is a wide aperture and right image
is a narrow one. Image Credit: Self
Aperture
at different settings. Credit:
http://www.goldfries.com/photography/digital-slr-beginner-understanding-shutter-speed-aperture-and-iso/
