Fast Prescans - Better Light ViewFinder 7 User Manual

Fast Prescans

The Fast Prescan checkbox in the main control
area selects between normal prescans (unchecked), per-
formed at exactly the line time and color balance (sen-
sitivity) selected, and Fast Prescans (checked), which are
performed at the highest sensitivity and shortest line
time that will still yield the same color balance and effective exposure. Fast prescans may exhibit more
noise than normal prescans, but this is often an acceptable trade-off for potentially far shorter prescan
times.
When a Fast Prescan is to be made, the control software checks whether the camera sensitivity
(color balance numbers) can be increased by 1/3 EV, or more, without exceeding the maximum set-
ting (i.e. 130) for any number, and whether the line time can be decreased by 1/3 EV (one click of
the line time button) without going below the minimum line time. If so, these adjustments are made
and the conditions are checked again, until no further adjustments can be made.
The overall color balance of the camera is not changed theoretically by this technique, since the
ratios between colors remain constant. However, over a large change in ISO slight shifts in color bal-
ance may occur. When an automatic color balance is done from fast prescan image data, the selected
color balance setting is adjusted based on image data obtained with a possibly much larger set of
numbers, leading to occasional, minor inaccuracies in the resulting balance.
If color balance is to be readjusted based on preview image data, a normal-speed prescan is
recommended for improved accuracy.
Fast prescans to be captured at high ISO settings will not "speed up" as much as those to be taken
at lower ISO, since less adjustment is possible before the color balance numbers reach maximum.
Fast Prescan option.
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