User's Guide to ShARCS

Table of Contents

Summary Table
Detector Characteristics
Filters, Grisms, Apertures, Polarimeter
Software Overview
Data Taker GUI
Filter & Aperture Wheel GUI
Image Display GUI
Sound server
Temperature Monitor
Observing Procedures and Tips
FITS Header Keywords

Data Archive
Mt. Hamilton Homepage

Image Display Software

The image display software for ShARCS is run on the computer covert with the command sharcsdisplay. This command will bring up a number of windows: Image Browser, sharcsdisp, Radial Profile, FocFit, and an xterminal for display text information and IDL output.


The sharcsdisp window (Figure 1) is the primary image display GUI for the ShARCS camera. Images are automatically displayed after they are written to disk. The compass rose will indicate which direction is North and the axes are in arcsecond units by default. As the cursor is moved around the image, the pixel positon and value will be displayed below the image as well as the minimum and maximum pixel values in the data. Above the image is displayed the file name and object name from the FITS header. When using the FWHM tool in the Image Browser, an estimate of Strehl for the selected object will be displayed above the image as well.

The radio buttons at the bottom of the sharcsdisp window allow one to choose what action is taken when clicking on a spot in the image. Zoom will zoom in on the clicked position, which Unzoom will do the opposite. Recenter allows one to pan the image, recentering the zoomed image on the pixel clicked. The FullImage button will resize the image to fit in the display window.

Figure 1: Image Display GUI, sharcsdisp.

The File menu (Figure 2) has two items Show Header and ReadFits. Show Header will bring up a GUI showing the text of the FITS header for the currently displayed image. ReadFits brings up a dialog GUI to select a FITS file in /data/sharcs/ to display.

Figure 2: File Menu

The color map used to display the images can be changed using the ColorMap menu (Figure 3). The last item in the menu, XLoadCT, allows one to load any of the IDL color maps if none of the pre-selected color maps is desired.

Figure 3: ColorMap Menu

The Axes menu (Figure 4) selects which axes and units to overlay on the image display. No Axes will overlay no axes on the image. Sky Arcseconds, the default, displays the X and Y axes in arcsecond units. Sky Pixels will display the axes in pixel units, with the lower left corner of the image display as coordinate (0,0). Note that the Real Detector Pixel X and Y coordinates are also displayed on the upper and right borders of the image. Detector Pixels displays the detector pixels values (which are rotated and flipped from the sky pixel coordinate system). If one wants to window the chip to read out only a sub-region, the Window GUI in sharcs_fe uses the detector pixel values for defining the region. A compass rose may also be overlaid on the image, indicating north and east by clicking on Show compass and hiden from view by selecting Hide compass. The orientation is read from the instrument position angle in the FITS header keyword TUBANGLE.

Figure 4: Axes Menu

Image Browser

The Image Browser GUI (Figure 5)is the main window for image display manipulation. Labeled buttons perform that function when pressed. The radio buttons to the left of the labeled buttons determine which functions are automatically done when a new image is displayed. Radio buttons that are on are depressed and red in color.

The newest button at the top of the window will display the most recent ShARCS image. In the parentheses will be the most recent image number or unknown if no image has been taken since sharcsdisplay was started.

The Display Image # button allows you display the image of your choice. Enter the desired image number in the box to the right. You may also increment or decrement the image number to be displayed by using the up and down arrows on the right.

The Subtract Image # button enables the subtraction of an image from the displayed image. Enter the desired image number to be subtracted in the box to the right. You may also increment or decrement the image number to be subtracted by using the up and down arrows on the right.

The full range button displays the current image over the entire range of pixel values, scaling the color map accordingly.

The sigdisp button displays the current image over a range of pixel values x sigma around the mean. Default is 12 sigma, but can be changed in the box to the right. Commonly used values are 1, 3, and 5 sigma in addition to the default.

The minmax button displays the current image over the range of pixels values specified in the boxes to the right.

The log button displays the current image logarithmically scaled over the range of pixel values specified in the boxes to the right.

The stats button displays the mean and standard deviation of the image pixel values.

The fwhm button calculates the FWHM, centroid, and estimates the Strehl of a source in the image. The measurements are displayed in the xterm window from which sharcdisplay was started in following format (for example):

 xcen      ycen     peak( g / r )     (x / y)fwhm npfwhm  (x / y)fwhm"  npfwhm"  
    47.5    55.6   10967. /  11215.   3.29 /  3.26  3.53   0.11 / 0.11  0.12
      flux     sky   strehl / congridstrehl
    227161.   -14.0   0.30  /   0.30

The x and y centroid from a gaussian fit of the object are xcen and ycen.
The peak flux of the source is calculated two ways: the peak of the gaussian fit (g) and the measured peak of the object (r).
xfwhm and yfwhm are the x and y FWHM calculated from the gaussian fit to the object in pixels.
xfwhm" and yfwhm" are the x and y FWHM calculated from the gaussian fit to the object in arcseconds.
npfwhm is the FWHM in arcseconds calculated directly from the number of pixels above half the peak value.
The total flux of the star is total (sky subtracted) counts inside the photometry aperture.
The sky flux displayed is the average per pixel as measured in the sky aperture.
The estimated Strehl is calculated twice, based on the peak measurements from the data and the gaussian fit: Strehl=peak/flux/factor, where factor varies depending on which filter is being used. Note that this Strehl is only an approximation, but should be indicative of the image quality.
In automatic mode, the algorithm finds the FWHM around the peak pixel in the image (note: sometimes this will find a bad pixel or cosmic ray, not a real object). In manual mode you will click on the fwhm button then click on the source in the image. Two circles will be overlaid on the image around the source, one showing the FWHM fitting region and another for the photometry calculation region. The radii for these two functions can be set using the Image Browser Config - Configure menu (Figure 8). The radial profile and FWHM fit will be displayed in the Radial Profile window (Figure 7).

The badpix button will remove the badpixels in the image (based on an existing bad pixel mask), replacing them with the median of the surrounding pixels. This is somewhat time consuming, but can be useful particularly when imaging faint objects.

The Move Tel button allows you to move the telescope by clicking on the image. This is particularly useful for positioning an object on a particular pixel in the array. Click on Move Tel, then click on the object, then click the position you wish to object to be. The telescope and optics in the ShaneAO system should move the proper distance and direction to put the target on the desired position on the chip.

The two IDL buttons allow IDL commands to be executed. Enter the command in the dialog box and press the IDL button to send it. The currently displayed image is called img in the IDL session and you can manipulate the image using regular IDL commands.

The reset IDL button sends an IDL retall command in case the Image Browser gives an IDL error or gets confused on which display window is which, or fails to display the new image. This is a good general fix to most problems that the Image Browser occasionally exhibits.

The hardcopy button sends the currently displayed image in the sharcsdisplay window to the printer in the 3-m control room (note, this is not currently functioning).

The focfit, focval, and focfit init are used for ShARCS image sharpening and not generally used by the observer. The focfit program fits a parabola to the Strehl of each image at various focus or other aberration mode values and prints the best focus value. In addition, focfit displays a zoomed view of the image around the point source being measured. The focval entry box is the focus (or image sharpening mode) value. The focfit init button initializes the focus fitting program using the focval entry and Strehl of the current image as the first data point. The focfit button adds new data points (Strehl and focval entry) to the parabola fitting program. The following procedure is typically used for focusing ShARCS with focfit:

  1. Determine the proper exposure time so that the white light internal calibration source does not saturate Sharcs, but still gives high signal-to-noise. Typically one uses the FeII filter.
  2. Check the auto fwhm checkbox in the image browser window.
  3. Take an exposure with ShARCS.
  4. Enter the current focus position in the focval entrybox.
  5. Push the focfit init button.
  6. Change ShARCS focus (mode 1 in the imageSharpen GUI in ShaneAO software).
  7. Take an exposure with ShARCS.
  8. Enter the current ShARCS focus position in the focval entrybox.
  9. Push the focfit button.
  10. Repeat previous 4 steps until you get a good focus. After 3 focus positions a plot will be displayed in the FocFit window and the best focus estimate will be printed in the sharcsdisplay text window.
Use a similar procedure for the other image sharpening modes to get the best possible strehl and internal alignment.

Figure 5: Image Browser GUI

Figure 6: Radial Profile display.

Figure 7: Text output.

Config Menu

The Config menu has two selections: Configure and Update newest file. Update newest file simply looks in the current data directory for the most recent file and displays it. Configure brings up a window where you can change the data path, the FWHM and photometry radii parameters for the FWHM/Strehl estimating routine, and if the new image always zooms to fill the display window.

Figure 8: Configure GUI.
Last modified: Sat Mar 26 15:11:16 PDT 2016