N08A29;31/33
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(Note) Strictly speaking, even if the same pulse width of Vinit is applied, the shutter speed differs for the period
corresponding to 1H width when the asynchronous shutter operation is executed in the pulse width control mode
(indefinite for 1H width).
Although an equal pulse width (value between 2Hs and 3Hs) is applied both for (A) and (B) in the figure below, the
phase relationship with the internal horizontal synchronous timing makes their shutter speeds different from each
other: (A) shutter speed = 2Hs and (B) shutter speed = 3Hs.
Vinit (A)
Vinit (B)
HD
(Internal horizontal
synchronous signal)
Example of 1H difference with same Vinit signal
(Shutter time: 2Hs)
(Shutter time: 3Hs)
1
2
3
1
2
Because of the above reason, consideration must be given to the fact that the exposure time becomes indefinite for the
period of 1H shutter speed when a Vinit signal that is not in synchronization with the internal horizontal synchronous
signal (HD) is input from the user side. Some of the countermeasures to be taken are as follows:
(1) Use only with the shutter speed that do not have serious impact even if the shutter speed is indefinite for a period of
1H.
••• No practical problem may be caused when the shutter speed is fairly long, say 100H width or longer because the
impact of 1H difference in exposure time over the signal level is relatively small.
(2) Synchronize the external trigger signal with the use of the LDV signal of the camera to keep the Vinit phase
relationship constant.
••• Control can be made in the absence of the infinite time of 1H by stabilizing the generation phase of Vinit against the
internal HD.
(Note) Since n does not have an upper limit, the exposure time can be prolonged to be more than one frame time. The
maximum exposure time to be employed, however, should be determined after implementing experiments based on
the conditions of the actual operation because a longer exposure time is accompanied by the degradation of S/N ratio
due to the accumulation of CCD thermal noises.
●
Vertical timing: Low speed (long exposure)/preset shutter/continuous/normal scan
Timing of long exposure mode
Internal signal
(internal
operation)
Image output
VD
(Vertical
synchronous
signal)
Exposure time
(nV)
FDV
Image signal
(digital)
1V=2074
Exposure time (nV)
Image (P) / exposure time
10
Image (P – 1)
Effective image period (2050)
Image (P+1) / exposure time
Image (P)
Image (P+1
Effective image period (2050)
* The detailed vertical timings of the respective effective image times are the same as those of “Vertical timing for continuous
shutter and without shutter”.
(Note) The long exposure operation is not compatible with the partial scanning.
(Note) The asynchronous shutter operation is not supported for the long exposure operation.