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The estimates are printed in the lois log and in the focus log; the final focus setting adopted, however, is that based on the minimum fwhm criterion. You are not obligated to accept this focus. The setfocus command and user button can be used to select another focus. If the focus script fails, or is aborted, or is still at the top or bottom of the sweep after a second sweep, the focus setting is restored to focbase.
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The images taken with this routine are test.fits images. The "save" flags setting will make a subdirectory for this focus run, in the main image data path for the rundate, to save named images for each focus step position. The name of the directory subdirectory matches the hh:mm:ss timestamp used for the focus run in the focus log.
The script normally stops if an acceptable star image is not available, either during acquisition or at any focus step, following retries. The conditioning flags setting causes all focus sweeps to run unconditionally to the end; however the focus setting is restored to focbase at the end regardless of results- this mode of operation merely updates the focus log.
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- Go to the home directory for obslemi in the console where you started LOIS.
- type ./abscript
- wait some seconds, and the LOIS log should indicate the script is aborting.
- The script will set the focus back to the value of focbase.
- now type ./abscript clear; if you fail to do this the focus and other scripts will abort immediately on startup.
Parameters
The defaults for the focus script, and other relevant parameters for the operation such as the size of the aperture masks for photometry, are defined in the definitions file for LMI. (q.v.dct_lmi_defs.tcl).
TESTFOCUS LOG
A sample log entry:
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Focus in place () .5 (1, 1) results run
2013/05/29 05:09:43
Current tube temperature is 0.0
Focus run in nominal band internal Focus binned 2:2 1 per step
Test subframe 6: 1558:1500, 300 x 300
570 104,101:7445.00, Cent=101.76:100.90 Fwhm=12.33 Mag=8.48 Sky=1177.67 fom= 0.1836, 1.56 0,0
620 101,102:9742.00, Cent=100.75:101.74 Fwhm=10.86 Mag=8.32 Sky=1159.13 fom= 0.2073, 1.56 0,0
670 102,102:9511.00, Cent=101.24:101.99 Fwhm=11.00 Mag=8.40 Sky=1188.90 fom= 0.2179, 1.56 0,0
720 101,102:16209.00, Cent=100.62:101.97 Fwhm=8.59 Mag=8.29 Sky=1130.09 fom= 0.3356, 1.56 0,0
770 101,102:18143.00, Cent=100.47:102.00 Fwhm=8.29 Mag=8.27 Sky=1130.08 fom= 0.3687, 1.56 0,0
820 101,102:15771.00, Cent=100.48:102.24 Fwhm=8.83 Mag=8.28 Sky=1137.33 fom= 0.3235, 1.56 0,0
870 101,101:13418.00, Cent=100.92:100.60 Fwhm=9.46 Mag=8.32 Sky=1146.34 fom= 0.2856, 1.56 0,0
920 99,102:10967.00, Cent=99.03:101.68 Fwhm=10.01 Mag=8.40 Sky=1140.93 fom= 0.2512, 1.56 0,0
970 101,104:7307.00, Cent=100.82:103.22 Fwhm=12.13 Mag=8.52 Sky=1230.03 fom= 0.1870, 1.56 0,0
2013/05/29 05:12:42
Best focus at 770 fwhm = 8.29 tube temp 0.0
Parabolic fit to fwhm data: X= focpos - (770)
Parabolic Fit constants 8.88961038961039e-5X**2 + -0.0020633333333333333X + 8.685064935064936
best focus 781.6053080107134 from parabolic fit
Best focus at 770 fom = 0.36873 tube temp 0.0
Parabolic fit to fom data: X= focpos - (770)
Parabolic Fit constants -3.904813852813855e-6X**2 + 8.949333333333323e-5X + 0.3273380086580087
best focus 781.4593597424424 from parabolic fit
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- Fifth line- the (internal) subframe position and size after acquisition- it is slightly larger than that used for acquisition.
- Next 9 lines- the individual focus measures, giving focus value, max pixel x, y and signal in ADUS, centroid x, y, FWHM, instrumental mag., sky background, figure of merit, and actual exposure time. In this case the nominal exptime was increased by a factor of 3.
- Fourteenth line- the time stamp representing the end of the focus sweep.
- Fifteenth line- The best focus based on minimum fwhm with the corresponding fwhm value and the tube temp.
- Next 3 lines- the coefficients of the parabolic fit to fwhm vs focus and the minimum fwhm according to that fit.
- Eighteenth line- The best focus based on maximum fom with the corresponding fom value and the tube temp.
- Next 3 lines- the coefficients of the parabolic fit to fom vs focus and the maximum fom according to that fit.
Note: The focus value from In a results run, the focus offset was set automatically from value in the Fifteenth line is the one set automatically by the script.
Note: The fom or figure of merit is defined as the ratio of the peak pixel in ADUS to the total aperture photometry flux- here, the flux is based on the given instrumental magnitude and a zero point that has a flux of 1.0 ADU/sec at instrumental magnitude of 20.0. The more sharply focused the star, the larger the fom. The use of fom generally assumes the inst. mag is constant across the focus sweep, which is not strictly true in some cases.
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- The acqtry parameter is not honored.
- Changing the focus takes too long, because it is being run open loop.
LMI Definitions Applicable To The Focus Script
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