Better Light ViewFinder 7, Руководство пользователя

Страница: 27 / 99

27
Line Time
These up/down pushbuttons select the integration time for each line in a
scan, and are the digital equivalent of the shutter time. As with film, the primary
controls for determining exposure are the lens aperture and the line time (shutter
time) along with the amount of light (which is also controllable to some extent in
many studio setups).
The line time is adjustable in 1/3 EV (f-stop) increments, from 1/8 second per line up to 1/240
second per line (model series 4000, 6000 and Super 6K™) or 1/160 second per line (model series
Super 8K™). Longer line times increase the CCD’s time available to absorb light, but also increase
the overall scan time and the dark current noise. Longer line times also increase the susceptibility of
the CCD to temperature changes that can degrade image quality.
Hold the Option key down and click on the Increase or Decrease buttons to jump to the
maximum or minimum line time values.
The Line Time readout displays the selected time per line, in traditional photographic increments.
The actual integration time used by the system for each line time varies slightly according to the Line
Sync mode selected in Preferences . The Line Sync mode chooses among line times that are exactly as
displayed ( Exact mode), or line times that are multiples of the local AC power line half-period (the
time per half-cycle of the local AC power), when 60 Hz or 50 Hz are selected in Preferences .
By using line times that are precise multiples of the AC power half-period (60 Hz/50 Hz
options), any minor variations in image highlight intensity caused by AC line frequency
flicker can be substantially reduced or eliminated.
Longer line times become increasingly effective at rejecting these intensity variations. Not all line
times will sync to the AC line frequency, and the shortest line times are too fast to use with sources
having significant flicker, as it may be possible in some cases to expose an entire line between the
bursts of light from certain sources (while there is little or no light). Low wattage tungsten lights or
fluorescent lamps with magnetic ballasts are the biggest offenders.
Line times that cannot be synchronized to the selected AC main frequency will be dis-
played in RED. Use these red settings with caution!
These line times may still be perfectly usable with sources that don’t produce appreciable flicker.
Line times that are synchronous to the chosen AC main frequency are displayed in BLACK, as are all
line times when
Exact Line Sync is chosen. See Appendix C for more information about Line Times
and Preferences for details on choosing the appropriate Line Sync setting (60 Hz is the default set-
ting).
Line Time control.