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LIRIS Overheads

Hereafter you find some characteristic overheads for filter changes etc. Due to the large number of possible combinations we timed only a few representative instrument operations, and give average values as a rule of thumb.

Filter change overheads (sec)
 
to
from
z J H Ks
z 0 18 63 47
J 80 0 58 43
H 34 39 0 68
Ks 54 54 55 0
average: ~50 seconds

Changing imaging and spectroscopic modes (sec)
 
to
from
image (J) spec (zj) spec (hk)
image (J) 0 78 45
spec (zj) 43 0 69
spec (hk) 78 56 0

average: ~60 seconds

representative for other filters as well.


Changing imaging, polarimetric and coronographic modes (sec)
 
to
from
limage j lipol j lcor j
limage j 0 71 79
lipol j 45 0 53
lcor j 47 74 0

average: ~60 seconds

representative for other filters as well


On-target Movement overheads:
 
12" dithering offset (imaging, tracking): 8
24" dithering offset (imaging, tracking): 11
12" nodding offset (spectroscopy, tracking): 12
12" nodding offset (spectroscopy, guiding): 33
Rotator angle from 0 to 90 or 90 to 0 degrees: 120

Exposure related overheads:
 
clear-reads (default N=3. Only before first exposure at each new position.) Nx0.8
Imaging read-out time, mndr 1 1 (default): 2
        mndr 2 1: 3
Spectroscopy read-out time, mndr 4 1 (default): 5
        mndr 8 1: 11
Time until image is displayed after readout: 4
Time until image is saved after readout: 4
Time until you get the prompt back after readout: 2

Please note that while dithering or nodding, after the last exposure is taken at a given position, the chip is readout while moving to the next position, so only the larger overhead (movement or readout) applies.



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Contact:  (LIRIS Instrument Specialist)
Last modified: 12 December 2012