Photron fastcam sa2 Hardware Manual page 41

 When the auto exposure function is operating, the camera will not perform a shutter operation with
an exposure time longer than the shutter value set here.
These settings are shown in the diagram below.
+ RANGE
TARGET VALUE
- RANGE
If the image level being output (the average value of the area set with AREA) is ①, ②, or ③, the
function operates as below.
For position ①
Since the image level being output is higher than the range TARGET VALUE±RANGE, the function
operates to close the shutter (shorten the exposure time).
For position ②
Since the image level being output is lower than the range TARGET VALUE±RANGE, the function
operates to open the shutter (lengthen the exposure time).
For position ③
Since the image level being output is within the range of TARGET VALUE±RANGE, the operation
of the shutter is not varied.
 The DS SHUTTER function is inactive while the AUTO EXPOSURE function is being used.
 When the RANGE setting is a small value, the range of the desired image output level narrows.
 If the RANGE value is made smaller than necessary, the image level is difficult to place in the
desired ③ position.
In this case, the variable shutter operation cannot place the image level in the desired ③ position
and a phenomenon occurs where the image output level is unstable.
When a situation like this occurs, it can be resolved by making RANGE a larger value.
①
③
③
②
29 FASTCAM SA2 / SA2 RV Hardware Manual