Page 102 - Friedman Archives

102 Quick Guide for the Impatient User

VERY important!) the optics only generate an image circle large enough
for an APS-C-sized image sensor, NOT large enough to cover a full-frame
sensor. This tactic saves cost and weight, and makes the lens easier to
manufacture.
APO – Normal glass will bend light much like a prism does – the red
colors get bent a little more than the violet, and all colors in between are
bent at different rates. This is fine for average lenses where the precision of
the image is not super-critical; but in long telephoto lenses this
phenomenon can contribute to slightly fuzzy images. A really, really sharp
picture requires that all optical rays converge on the same point – an
extremely difficult task if the light is bent differently for different colors.
Enter the APOchromatic glass element, or APO for short – this kind of
glass bends all visible light waves by the same amount, producing
noticeably sharper images than equivalent lenses using standard optical
glass. A lens marked “APO” means it has one or more optical elements
made of this special material.
G – This is Sony’s (and Minolta’s) designation for their “Pro” line of lenses
– they can be rather expensive, but they are the best to be found anywhere
from any manufacturer. I own several.

Before going on to the next two definitions, it is worth pointing out that
Minolta’s original autofocus mechanism, which dates way back to 1985,
used a single motor in the camera body which drove every lens through a
“screwdriver” blade (which you can see sticking out of the lens mount
when you remove the lens, Figure 3-24). The advantage of this design
was that you didn’t have to put a motor into every single lens (like Canon
did with its EOS system). All Minolta and Sony autofocus lenses made
since that time have used this mechanism to good effect.

Recently, however, Sony has started to offer lenses that have motors built-
into them, called SSM and SAM lenses. This was done to reduce the
autofocus noise when shooting movies.

SSM –There are some high-end lenses which incorporate a SuperSonic
Motor (SSM) in the lens. This is a fast and quiet focusing mechanism
which can be found in some of the more expensive telephoto lenses
because it can reduce the strain on the camera body’s focusing motor. The
mechanism is very similar to Canon’s USM (Ultrasonic Motor)

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