‘
Focus, Automatic Continuous
’ is an on (1) / off (0) control that sets whether the optical
auto-focus feature of the camera lens is active or not. When active the lens will move in or
out to main focus of a subject near the centre of the field of view. This auto-focus
algorithm is not perfect so focus can sometimes shift in an undesirable way. When this
setting is on the value for the ‘
Focus, Absolute
’ setting will be disregarded. When ‘
Focus,
Automatic Continuous
’ is set to 0 (off) the lens will stay in the position it was last in during
auto-focus until a value for ‘
Focus, Absolute
’ is sent to the camera. This means that
‘
Focus, Automatic Continuous
’ can be used as a ‘one-touch’ automatic focus control (i.e.
you enable ‘
Focus, Automatic Continuous
’ and wait till the desired focus is achieved for
you then you set ‘
Focus, Automatic Continuous
’ to 0 and that focus will be maintained
and fixed until you either re-enable ‘
Focus, Automatic Continuous
’ or you send a value to
the ‘
Focus, Absolute
’ control). In most circumstances ‘
Focus, Automatic Continuous
’
should be disabled (set to 0) when using the AF51 with an optical instrument coupled to
an eyepiece and for proper afocal eyepiece projection coupling this fixed focus should be
at infinity.
‘
Focus, Absolute
’ gives you manual (or programmatical) control over the focus to
produce a fixed focus of the lens at a position determined by the value supplied for this
control. The value in this control will only be settable or alterable when ‘
Focus, Automatic
Continuous
’ is set to 0. The value for ‘Focus, Absolute’ can be varied from 0
(representing focus at or just beyond infinity) to 1022 (representing focus at about 3 cm
from the front of the lens, the closest focus possible with this lens). For most work using
the AF51 coupled to an eyepiece the focus should be fixed at infinity (at or near a value of
0). In practice I find that this voice-coil focus mechanism can get a bit ‘sticky’ in that if
focus has been held fixed for some time then you might need to increase or decrease the
focus value quite a bit before it actually changes the voice coil position (with a jolt) and, at
that point, more fine continuous control is again restored.
OptArc AF51 Camera Page 32 of 99 User Guide v1.02
