SBIG ST-8300 Manual
Here we’re asking for a 1.0-second dark frame of the full CCD. Click the
OK
button and in a few seconds you’ll see an image that looks a lot like the
Image 1
from the tutorial. Hot pixels, readout glow and salt-and-pepper
noise, they’re all there. Congratulations: You’ve just taken your first dark
frame! That wasn’t so hard was it?
Let’s experiment with the settings in the Grab dialog. Try changing the
Exposure Time
to 10 seconds and grabbing another image but this time
watch the LED on the back of the camera. It blinks while the camera is
exposing the image. That’s a handy thing to remember when you’re in the
observatory.
Don’t bump the telescope when the LED is blinking
.
Anyway, the new image should look just like
Image 2
. Try setting the
Exposure Time
back to 1.0 and the
Dark frame
to
Also
. What happens
here is the camera takes a
dark frame
first, and then takes a
light frame
,
subtracting
the
dark frame
from it. The result should be uniform noise
without
hot pixels
and without
readout glow
.
Had we had the camera on the telescope we would have seen the object
but because we had the nosepiece covered we took a
dark subtracted image
of the dark. If you take enough of these, and stare at them long enough
you’ll see all kinds of patterns in the random noise, including even pictures
of Elvis!
You can read about the other items in the
Grab
dialog by clicking the
Help button
, but in general the
Grab
command is used to
take a single
image
and optionally do an
automatic dark subtraction
.
Note
: Dark subtracted images have an offset of 100 ADU added to them to
ensure values near zero are not clipped.
Focus Command
Using the
Grab
command to focus your telescope would drive you crazy,
taking a single image at a time, tweaking the telescope etc. Instead we use
the
Focus
command, which is like
Grab
but it takes image after image
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Содержание ST-8300C
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