Page 99 - Friedman Archives

Lenses 99

3.12.2 CROP FACTOR
The first thing to be
aware of is that
pictures taken on your
A77 II will look more
“zoomed in” than
using the same lens
with the same settings
on a full-frame camera
body. (This is true of
most DSLRs from any
camera manufacturer.)
This is because the
sensor used in your
camera is smaller than
that of a full 35mm
frame. Have a look at
the illustration shown Figure 3-21: Whereas a full-frame lens (like those used
in Figure 3-21, which for 35mm film cameras, top) projects a large image
illustrates how the circle that will fill a 35mm frame, the designed-for-
digital sensor is digital “DT” lenses (bottom) are designed project a
smaller than that of smaller image, just enough to cover the smaller APS-C
35mm film, and also image sensor.
how the newer “DT”
lenses (described in a few pages) are optimized for this smaller sensor.

Also have a look at Figure 3-22, which shows what happens when you put
an older lens (designed to cover the entire 35mm frame) onto a camera with
a smaller sensor: the sensor “sees” less of the image that the lens produces.
The upshot is that a 50mm lens on a film camera will appear to act as a
75mm lens on a digital camera, and a 200mm lens will behave the same as
a 300mm lens on a film body. This is the “focal length magnification”
factor (sometimes called “crop factor”) that you may have read about; for
the Sony A-mount cameras the focal length is effectively multiplied by 1.5.
This is great news if you’re a sports or nature photographer, for when
shooting on an APS-C-sized sensor (which your cameras has) your 200mm
lens suddenly becomes a 300mm lens. It can be bad news for travel and