IV. SHARPNESSEVALUATION 29
Motion Blur
Camera or Subject
MovementAfter
FocusLock
Diffraction
bound to looksofter than it would at greater viewing distances or lower magnification.
Therefore, ifprinted output, especially at 8.5" x 11" or less, is the final objective, it’s
bestnot to rely completely on monitors to judge image quality. To prove thispoint, we
encourage you to compare your printed imagesto the on-screen versions.
When high-resolution imagesare enlarged to 100% magnification on screen, image
defectsof any kind are accentuated. One such defect that is often mistaken for
inaccurate focusing when viewed atsmaller magnifications is motion blur. Thiscan be
caused bysubject movement and/or camera movement, and is especially likely to occur
atrelatively slow shutter speeds. Remedies include shooting with a tripod to eliminate
camera movement, using an Image Stabilizer lensduring hand-held photography to
minimize the effectsof camera movement, and using either high shutter speeds or
electronicflash to freeze subject movement. Secondary “ghost” images in flash photos
can be minimized or eliminated byusing faster sync speeds and/or lower ISO speeds or
smaller aperturesto reduce the effect of ambient light.
The closer the subject, the more criticalaccurate focusing becomes. One potential
problem to avoid iscamera or subject movement after focus lock. This can happen more
easilythan one might think, especially during hand-held photography when the camera
isset for One-Shot AF. Even slight camera movement or subjectmovement after focus
lockcan result in soft images, particularly when shooting at wide apertures with narrow
depth offield.
Diffraction isan opticalphenomenon in which light waves pass around the edges of an
objectand enter the shadowed area of that object†. In photography, diffraction flare
often occurswhen images are shot at small apertures with short focal length lenses. The
visualeffect is a softening of fine detail that cannot be corrected in post-processing. If
you are concerned aboutthis optical phenomenon, we recommend avoiding apertures
smaller than f/16 with wide-angle lensesand wide-angle zooms.
†EFLensWork III