This is the only option that encompasses all types of observation.
It offers you the following choices:
- Auto-dithering or you can define your own dithering pattern
- Combined Offsets: do you want the autoguider to follow the
guidestar when you offset?
- Note: For large offsets (>?? arcsec) this should be set to
no. The guidestar will fall outside of the tracker chip after
the offset and a new one will have to be selected
- Return to Origin: do you want the telescope to return to
the original position after each dither pattern?
- This should be set to true if you want to perform
the same dither patter with more than 1 filter inside the same
OB. Otherwise, the dither pattern of the 2nd filter will start
at the last dither position of the first filter.
- Filter: should be the same one as you used in your
aquisition to minimise overheads
- Subexposure time: How long do you want each exposure to be?
- Number of Subexposures: How many exposures do you want in
the dither sequence?
- This number can be 1 if you only want 1 exposure
- If you are defining your own dither sequence, this number must
match the number of offsets you have given
- CCD Binning Mode 1x1 is default
- Observation Type choose from menu to reflect the purpose of the observation
P2PP panel with
The above example shows an OB comprising a sequence of:
- An aquisition template that will execute a simple preset, turn
the autoguider on, and put the V/89 filter in the beam
- Take 5 dithered exposures of 120 seconds each through the V/89
filter in a dithering pattern optimised for 5 exposures
- Autoguider follows the offsets and doesn't lose the guidestar
- Returns to the original preset position after dither
sequence is finished
- Take 3 dithered exposures of 20 seconds through the B/123
filter in a user defined dither pattern.
- The 1st exposure is offset from the preset position by
- The 2nd exposure is offset from the 1st position by
- the 3rd exposure is offset from the position of the 2nd
exposure by 500,480 arcseconds (i.e. the 3rd exposure should be
taken -60,-60 arcseconds from the preset position)
- Note: The offsets are cumulative!
- The telescope does not return to the preset position since
Return to Origin = false
- Take a single exposure of 500 seconds through the I/203 filter at
the position of the 3rd exposure of the above dither
- This happens since we did not set Return to Origin =
true in the preceding part of the OB
Not strictly a science exposure, but certainly something you need to
know about! In particular, the fact that a focus sequence takes about
10 minutes to complete. You have to be patient!
Within the template, one needs to define:
You should use the default values in all cases. The only parameter
you need to change is the Filter you wish to use
- Filter: Which filter you wish to focus in?
- Sub-exposure time: How long you want each exposure to be?
- Number of sub-exposures: How many exposures do you want to define the focus sequence?
- Telescope Focus Offset: How many encoder units do you want to move M2 by between each exposure?
- Image charge shift: How many pixels do you want each image of the star separated by?
Click here to download a standard
Focus OB (for the V/89 filter). You can then import this
directly into your P2PP, duplicate it and edit the duplicates to make
Focus sequences for other filters.
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Last modified: Thu Jul 31 2003