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Getting Started
T
total
=
3 s, then the true frequency would be
f
=
1
3 s
=
0
.
3333
. . .
Hz,
but [Shift][Frequency] would only display 0.333 Hz. This does not
mean that the timing is degraded to match the displayed frequency,
only that there are additional digits not shown. Similarly, if the
operator should set up a sequence timing with a frequency as the
controlling parameter, for example by entering 3 Hz, then the full
precision of the SR470 would be dedicated to producing true 3 Hz
cycles, while the
delay times
would be the parameters that may be
truncated for display.
Because the
exposure
and
postdelay
portions of the timing sequence
each contain a transition between the open and closed states, the
minimum
practical
value for those two delays is given by the actual
opening
/
closing time of the shutter head. The SR470 queries the
shutter head to determine this interval, and if either T
exp
or T
post
is
shorter than the opening
/
closing time, the
Limit
enunciator to the
left of the numeric display will be illuminated. Delay times can be
selected to be as low as 1 ms for both of these parameters, even if that
is less than the opening
/
closing time. The maximum rate, which is
related to the opening
/
closing time, can be queried over the remote
interface; please see
§
2.5.5.
There are two possible frameworks,
delay priority
and
frequency pri-
ority
, for entering timing parameters, which depend upon whether
the individual delay times are the most important parameters, or
on whether the complete sequence duration is the most important
parameter. We will discuss these separately in the next two sections.
1.2.4.3 Delay priority mode
The default framework for entering timing information is called
de-
lay priority
. In
delay priority
mode, the user may directly enter the
three timing delay parameters T
pre
, T
exp
, and T
post
. If these values are
changed, the total sequence duration T
total
will change as an
elastic
parameter
, remaining equal to the sum of T
pre
, T
exp
, and T
post
. The
frequency
f
also changes, since
f
=
1
/
T
total
.
In this framework, T
total
and
f
might best be regarded as
read-only
values, since it is not obvious which of the three component delays
should be altered when the the total is changed.
1.2.4.4 Frequency priority mode
A second timing framework is called
frequency priority
. In
fre-
quency priority
mode, the total sequence duration T
total
, or equiv-
alently
f
=
1
/
T
total
, is considered to be the most important timing
parameter, while T
post
is considered to be the
elastic parameter
. The
SR470 enters into
frequency priority
mode when the operator enters
SR470 Shutter Controller
