Pentax ZOOM 105-R Operating Manual page 21

D
While continuing to press the shutter release button
halfway, re-aim the camera or recompose the picture,
then fully depress the shutter release button.
Notes:
• You can cancel focus lock simply by taking your finger
off the shutter release button.
• When in the Consecutive Shooting mode, focus lock
cannot be used.
Hard-to-autofocus subjects
Like many other autofocus cameras, this camera's
autofocus system is highly precise, but it may not
focus as you wish on certain subjects. In such
cases, use the focus-lock technique on a subject
which is both near the actual one and at an equal
distance from the lens.
Subjects which are hard to autofocus include:
1. Black objects like hair, which don't reflect much
light (and therefore don't reflect infrared autofocus
beams}.
2. Wire netting, latticework, iron exercise-bars, etc.
3. Flickering light sources such as neon signs,
fluorescent lamps, TV images, sunlight coming
through trees, etc., and subjects illuminated by
these light sources.
4. Glossy and reflective surfaces like glass, mirrors,
car bodies, etc.
5. Fast-moving objects, like trains in motion.
6. Water jets, water surface, smoke, flame, fireworks,
etc., which have no distinct or consistent form, or
a subject in mist.