| kpnofocus | noao.obsutil | kpnofocus |
kpnofocus -- Determine the best focus from KPNO focus images
kpnofocus images
Radius - the radius enclosing the specified fraction of the flux
FWHM - a direct FWHM from the measured radial profile
GFWHM - the FWHM of the best fit Gaussian profile
MFWHM - the FWHM of the best fit Moffat profile
The labels in the graphs and output will be the value of this parameter to distinguish the different types of size measurements.
When selecting objects with the image cursor the following commands are available.
? Page cursor command summary g Measure object and graph the results. m Measure object. q Quit object marking and go to next image. At the end of all images go to analysis of all measurements. :show Show current results.
When in the interactive graphics the following cursor commands are available. All plots may not be available depending on the number of focus values and the number of stars.
? Page cursor command summary a Spatial plot at a single focus b Spatial plot of best focus values d Delete star nearest to cursor e Enclosed flux for stars at one focus and one star at all focus f Size and ellipticity vs focus for all data i Information about point nearest the cursor m Size and ellipticity vs relative magnitude at one focus n Normalize enclosed flux at x cursor position o Offset enclosed flux to by adjusting background p Radial profiles for stars at one focus and one star at all focus q Quit r Redraw s Toggle magnitude symbols in spatial plots t Size and ellipticity vs radius from field center at one focus u Undelete all deleted points x Delete nearest point, star, or focus (selected by query) z Zoom to a single measurement <space> Step through different focus or stars in current plot type :beta <val> Beta parameter for Moffat fits :level <val> Level at which the size parameter is evaluated :overplot <y|n> Overplot the profiles from the narrowest profile? :radius <val> Change profile radius :show <file> Page all information for the current set of objects :size <type> Size type (Radius|FWHM) :scale <val> Pixel scale for size values :xcenter <val> X field center for radius from field center plots :ycenter <val> Y field center for radius from field center plots The profile radius may not exceed the initial value set by the task parameter.
This task is a script based on the task starfocus . The details of the algorithms and display modes are given in the help for that task. The purpose of kpnofocus is to provide a simpler task with fewer parameters because the format of the multiple exposure images is given by header keywords.
As a summary of the algorithm, the center of each star image is found using centroids, a background is determined from the mode of a sky annulus, and the enclosed flux profile is measured. The PSF width is then the radius enclose a specified fraction of the flux. Alternatively a direct FWHM from the radial intensity profile, a FWHM for a Moffat profile fit to the enclosed flux profile, or a FWHM for a Gaussian profile fit to the enclosed flux profile may be used.
If a saturation value is specified then all pixels within the specified measurement radius are checked for saturation. If any saturated pixels are found a warning is given and ignore_sat parameter may be used ot ignore the measurement. If not ignored the object will still be indicated as saturated in the output log. In a focus sequence only the saturated objects are discarded and not the whole sequence.
To use this task consists of specifying a focus image name. Multiple images could be analyzed together but this is uncommon. The task will then display the image, using the current parameters of the display task, if the image is not already in the display. The user then marks the first exposure (the top one) by pointing the image cursor and typing m. This may be done for more than one star if desired. After all stars to be used are marked type q to go to the graphical analysis.
A plot showing the variation of the PSF width and ellipticity with focus is shown along with a magnitude weighted, parabolic interpolated estimate for the best focus. One may delete bad points with the cursor d key. To exit and record the results to a logfile use the q key. There are many graphical display options for more sopisticated analysis such as variations with position. The best thing to do is to try the various keystroke commands given in the CURSOR section. For details about the various plots see the starfocus help.
The other task parameters allow setting the enclosed flux level, the object and sky apertures, and the type and scale of the reported PSF size. The log filename may also be specified.
1. A multiple exposure frame is taken with 7 exposures of a bright star, each exposure shifted by 30 pixels using the version of the ICE software which records the focus information in the keywords FOCSTART, FOCSTEP, FOCNEXPO, and FOCSHIFT.
cl> kpnofocus focus1 <The image is displayed and the image cursor activated> <The bright star is marked with 'm'> <Marking is finished with 'q'> <A graph of FWHM vs focus is shown> <Exit with 'q'> NOAO/IRAF IRAFV2.10.3 valdes@puppis Fri 15:48:01 12-Nov-93 Image Column Line Mag Focus FWHM Ellip PA SAT 36inch1 536.63 804.03 0.07 4660. 13.878 0.06 -11 535.94 753.28 -0.12 4680. 8.569 0.09 89 535.38 703.96 -0.08 4700. 5.164 0.11 -88 537.12 655.36 -0.02 4720. 3.050 0.08 -77 534.20 604.59 0.00 4740. 4.336 0.11 74 534.41 554.99 -0.00 4760. 9.769 0.09 -35 534.83 456.08 0.16 4780. 12.569 0.13 -10 Best focus of 4722.44 with FWHM (at 50% level) of 3.02
The estimated best focus is between the 4th and 5th focus setting at a value of 4722.4 and the best focus FWHM is 3.02 pixels.
imexamine, implot, pprofile, pradprof, psfmeasure, radlist, radplt, radprof, ranges, specfocus, splot, starfocus .endhelp
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This file last updated on 14 Nov 2001