Diffraction SBIG STC-428-OEM, Руководство пользователя

Страница: 20 / 44

SBIG STC-428-OEM CAMERA
USER’S MANUAL
20
In comparison, our previous generation STF-8300-OEM CCD camera has a
typical read noise figure of 9.3 electrons, and can record a maximum of 25,000
electrons in a single exposure. The noise performance is about the same, but
the total dynamic range achieved is over six times greater.
The STC-428-OEM automatically performs the subframe exposures internally,
so they appear from the outside to be a single exposure. The camera also
automatically adjusts the number and duration of the subframes to try to
achieve the target Subframe Duration . The actual subexposures may be slightly
longer if the requested exposure is not an exact multiple, as explained below.
Subexposure Duration must be at least 1 second. This allows ample time for the
stacking to occur after each subframe is read out into the camera's internal
memory.
When you request an exposure, the camera automatically calculates an actual
subexposure duration and number of subexposures, based on the target
Subexposure Duration, according to the following rules:
•
If the exposure time is less than twice the Subexposure Duration , a single
exposure will be taken
•
If the exposure time is greater than 16 times the Subexposure Duration ,
then the total exposure time will be divided by 16, and 16 subexposures
will be taken and stacked.
•
If the exposure time is an exact multiple of 2X to 16X the Subexposure
Duration , then the appropriate number of subexposures of the target
duration will be taken and stacked.
•
If the exposure time is not an exact multiple, then the Subexposure
Duration will be increased by the minimum amount required to make an
even number of 2 to 16 exposures. For example, if you have a Subexposure
Duration of 10 seconds and ask for an exposure of 25 seconds, you will get
two subexposures of 12.5 seconds.
This approach makes it easy to adjust the total exposure time as needed,
without having to worry about always adjusting the subexposures manually.
If you always want the maximum number of subexposures, then leave the
Subframe Exposure set to 1 second.
On the other hand, if your shorter exposures are not going to cause sensor
saturation, you may wish to avoid the extra read noise for short exposures.
You may therefore wish to increase the
Subframe Exposure target to 10
seconds.
If you are taking very long exposures at very low light levels, then you may
wish to set the
Subframe Exposure target to 30 to 60 seconds or more.
As a general rule, the ideal Subexposure Duration target should be modestly
below the level where you expect to see sensor saturation occur. That provides
the maximum dynamic range with the minimum extra read noise.