LAICA Users Manual

J.W. Fried



Design of the instrument

LAICA is installed at the prime focus of the 3.5m telescope. The design of the instrument itself is very simple: the light is focussed by the 3-lens corrector on the CCD array. Located in front of the array are the filters and a shutter. The CCD array consists of 4 CCDs with 4x4 k pixels each. The image scale is 0.224 arcsec per pixel. Read out of the CCDs is low-noise (around 10 electrons) and fast (< 1 minute). The filters are stored in a magazine which holds 20 filters; the desired filter is brought into the beam by a grabber. There are currently 12 filters available, a standard broad band Johnson and an SDSS filter set. The instrument is controlled with a GUI.

The arrangement of the CCDs is shown here as CAD image and a true foto here . In order to get a contiguous field, one has to fill in the gaps between the CCDs, i.e. 4 telescope pointings are needed for full coverage of a 1 square degree field (see illustration). There is a macro (@@ expose) to facilitate this and procedures to assemble a mosaic of the 16 images will become available (see here). The data are stored on disk in FITS format. Each exposure creates 4 files, one for each CCD. If the root of the filename you entered in the GUI is eg. JAN12 , and you have already 10 files on disk, the next exposure will produce files JAN120011_1.fits, JAN120011_2.fits, JAN120011_3.fits, JAN120011_4.fits for CCD 1,2,3 and 4, respectively. The numbering scheme of the CCDs is:

N is up, E is left on the frames.

Important Properties of the CCDs

Each CCD is divided into 4 quadrants to ensure a fast read out. Four preamplifiers are located at the corners of the CCDs, so the 4 corners are read out first; this results in flip of the images, specific to each quadrant. In the final fits file the data are put together properly. An overscan is read out, too. If you look at a displayed image, the overscan of quadrants 1 and 4 (numbered in the same sense as the CCDs) is stored "to the left" of the actual data, the overscan of quadrants 2 and 3 "to the right" of the data. Each overscan is 52 pixels, so the fits files have 4200 by 4096 pixels, the data are from column 53 to 4149, the center of the CCDs is at pixel 2100,2048.

Starting LAICA

Note: since the computer environment is permanently subject to changes, the actual start procedure may differ from the one described here!
  • log in workstation "laica" , for userid and password ask the local staff.
  • enter: startlaica in window labelled instrument, or click into the screen with the right mouse button and click on the roll-down menue "start laica". This will open the control gui with standard settings of parameters.
The use of the GUI is self-explanatory; familiarize yourself by playing with it. A real time display of the data will open automatically with the camera attached. The Auto scale button sets the scale of the displayed image such that the whole array is displayed during read out. The Auto Set Cut Levels button sets the low and high cuts.

To get this manual on-line click on the Help button in the GUI.

Note that the behaviour of the terminals is not equal (which it should be of course). The guider does not run properly on the dospan terminal, open it on one of the flat screens of PC o2k.

When you start your observing run make your own directory in the area given to you by the local staff, eg. by
mkdir mydata
and change to this directory by the command
cd mydata
. Make sure that the correct path is entered in the GUI. Now start three parallel MIDAS sessions (take care that they start on the same area you are sending your data to!), one for running a receiver which converts FITS to MIDAS, and another one for quick look of the data and one for using some macros which facilitate use of the instrument:

  • to start the MIDAS quick look, change to your directory in the xterm labelled MIDAS quick look, enter
    inmidas -p 33
    . Use this window to execute the prgs available for LAICA
  • to start the 2. MIDAS session, change to your directory in the xterm labelled MIDAS data reduction, enter
    inmidas -p 32
    . Use this window to look at your data.
  • in the xterm labelled receiver, change to your directory, enter
    inmidas -p 31
    Start the MIDAS receiver with
    @@ getfits
    when the MIDAS session has started. This receiver converts new FITS files to MIDAS format.
    Now you are ready to go!

    Preparing LAICA

    Telescope Settings

    The Calar Alto staff should check the tilt of the front ring and enter also the zero points for the telescope pointing. Make sure that this has been done, the values for these settings are given here.


    To take darks, you can either use the GUI, or the command @@ dark. To take a series of 3 darks with 0 secs exposure time, the most convenient way to do this is to use @@ dark 0 3 in one of the MIDAS sessions.


    Domeflats are inferior to skyflats which in turn are inferior to super sky flats, where super sky flat means a median of many science frames. Three papers which contain information relevant to this subject are Alcala et al. (2002), Feldmeier et al. ApJ 575,779 (2002) and Morrison et al AJ 113, 2061 (1997). Use kghostview to read these files.

    In any case, it is a good idea to take domeflats for all the filters you want to use. To take a domeflat,

    • close all doors
    • turn off all lights
    • turn on the flatfield lamp (150 Watt)
    • turn the telescope tracking off
    • move the dome to Azimuth=90, the telescope to t=0, delta=-27. Do not use the flatfield screen
    • open the mirror
    • make sure that nobody enters the dome!
    The following exposure times give well exposed flats:
           Filter    exp. time    
    	1  U         60           
    	2  B         10           
    	3  V          3         
    	4  R          1         
    	5  I          1          
    	6  B2        10        
    	7  black is beautiful
    	8  u'        30       
    	9  g'         5        
    	10 r'         1        
    	11 i'         1         
    	12 z'         1        
    The command @@ meter can be used to take a test exposure of a subarea of the CCDs and calculate the flux (ADU/second). It is useful to expose more than one flat and dark 0, too. Series of exposures can be easily obtained with @@ dark and @@ domeflat. For example, to take three dark 0 and three domeflats in the R filter one can use @@ dark 0 3 and @@ domeflat 4 1 3. The command @@ prepflat can be used to compute a median dark0 and a normalized flat.

    After flatfielding with skyflats the frames are flat to typically about 0.1%. The shutter of LAICA allows very short exposure times down to 0.1 second. For skyflats, the exposure time between 2 consecutive flats must be changed by a factor of about 1.2.


    To determine the telescope focus, turn on the tracking of the telescope, open dome and mirror. Take a focus series of a field on the sky using @@ autofocus. The exposure time should not be less than 10 seconds. Change the telescope focus by about 0.1 mm from exposure to exposure. Take 7 or more exposures, the focus is normally around 29.6. Load one of the 4 images into the MIDAS display and evaluate the focus series with @@ focus and then set the telescope focus. If the seeing is less than 1.5 arcsec it may be good to repeat the procedure with smaller steps! The LAICA software corrects the telescope focus for the small offsets between filters automatically.


    Taking a single exposure

    To take a science exposure, point the telescope to the desired position, and start the exposure either directly in the GUI or use
    @@ expose objectname exp.time
    Note that the pointed position is in between your CCDs! If you want to have this position on one of your CCDs use @@ center to center it on a CCD; eg. @@ center 3 will center the desired position on CCD 3.

    Flux calibration

    Flux calibration can be done with standard star fields, e.g. those of Landolt . LAICA uses 4 CCDs each fo which has its own wavelength dependent quantum efficiency. Additionally each CCD is divided electrically into 4 quadrants each of which has its own preamplifier. After flatfielding with skyflats the QE is corrected for to a few percent. For high precision photometry each quadrant msut be calibrated (see section treatment of LAICA data). The command @@ standard takes a series of 4 exposures with the field centered on each CCD.

    Taking a mosaic

    A mosaic can be taken very easily with the command @@ expose. The telecope position at start will be in the center of the mosaic.

    Example 1:
    You want to take a mosaic on the field around NGC6240, exposure time 60 seconds. First point the telescope to the center of the field, then use
    @@ expose NGC6240 60 1,4
    to take 4 pointings. The order of pointings follows the numbering used for the CCDs, i.e. starting from position 1 = NE,2 = NW, 3 = SW to 4 = SE.

    Example 2:
    Clouds have interrupted taking the frames in example 1 after the 2. pointing. To continue this sequence point the telescope to the center of the field, then use
    @@ expose NGC6240 60 3,4
    to take the pointings 3 and 4.

    Example 3:
    You want to dither on each pointing. Use
    @@ expose NGC6240 60 1,4 3,1

    to take 3 dithered exposures on each of the 4 settings, starting at position 1 in a predefined dithering sequence.
    Before starting an exposure, expose will prompt for checking the auto guider. If you answer "g", the shutter will open and the guider is set in full frame mode (see next section guiding). Select a guide star by clicking on it, and hit return in the expose command. Start the exposure by entering "e" and "resume" guiding. If you want to repeat one exposure during the sequence, you can do this easily since expose prompts for repeating an exposure.

    The program @@ gexpose differs from expose by the use of the guider. If you select a guide star inside the innermost red rectangle on the fullframe field, the guide star will stay on the CCD during the dithering sequence. After dithering, the program automatically starts to expose and guide. Should the guide star not be on the CCD during dithering, the program prompts for interaction.


    For exposure times longer than 1 minute it is necessary to use the autoguider. LAICA has its own built-in guider CCDs.
    To start the guider software, click into blank screen with the right mouse button pressed, and release it over START GUIDER . The guider must be opened in an own terminal, otherwise you get an extremely slow response on your input. Ask the local staff which terminal to use. You can choose between 2 guiders which are labelled east and west.
    • The mode Fullframe is used to read out the entire guider CCD with binning and a default exposure time, which can be increased if the stars in the field are too faint. Note that read out takes a few seconds. This mode is used to find a guide star. The outer red square indicates the useable area; if the star is outside, this may lead to malfunction. If the star is in the inner red square, it will always be on the guider when dithering.
    • To select a guide star, click on a suitable one with the left mouse button, wait for some magic to be done. The program sets a window of 80x80 pixels (default) around this star, which can be read out much faster than the full frame. The guider is ready to guide when the cross hair appears yellow.
    • To start guiding press Start. The program determines the center of gravity of the guide star after the first read out, and then moves the telescope such that the star is always at this reference position
    • With Pause the guider is set into pause mode (eg. when a door of the dome has to be moved). Pressing PAUSE again resumes guiding.
    • The button AutoStartResume starts or resumes guiding at the previously determined reference position automatically when the shutter opens. Note that this button sets the software in the mode described, it does not start or resume guiding!
    • It is recommended that the guider is always set in the AutoStartResume mode. If you take a mosaic, and the expose/gexpose command asks for input g=check guider, e=expose or t=terminate, answer with CR. The exposure starts, the shutter opens and the guider sees the field if in full frame mode. Click on a suitable star, and wait for some magic to happen. Once the guider has determined the centroid, it automatically starts to guide (the circle with the cross hair on the screen then turns from yellow to green). So the only input you need for the guider is the full frame modus and click on the guide star.
    Important to know:
    • The guider has no own shutter; to open the shutter, enter @@ shutter open in one of the MIDAS sessions. Starting an exposure will first close the shutter, wipe the CCD and then open the shutter again for exposing.
    • The guider stops automatically when the shutter closes. If the AutoStartResume button is pressed, guiding is automatically resumed when the shutter opens; if not, guiding has to be started with the START or resumed with the PAUSE button
    • With the button Exp.time you can change the exposure time; poor seeing requires longer exposure times. Reasonable exposure times are 2-3 seconds in the full frame mode and 7-10 for guiding.
    • With the button Telmove you can determine how much of the calculated offset of the telescope is actually corrected for. A good value is around 80, which means 80% of the calculated offset is actually send to the telescope
    • Usage of the guider should be made easy using the commands @@ expose which prompts for action of the observer and communicates with telescope, guider and CCD and @@ gexpose which automatically resumes observing after an exposure if the guide star of the previous exposure is on the guider CCD after exposing
    • The buttons mean and manual affect only the display of the data. Centroiding is influenced only by exposure time and the window size.
    • the bar which appears when guiding is 10 arcsecs long, the circle around the star has a diameter of 2*FWHM
    • The buttons FILTER moves 5 mag neutral density filters over the guider CCDs. Make sure they are in position out (button NOT pressed) if you don't find a guiding star.
    • If an exposure sequence had to be interrupted by some reason and one has to continue exactly on the same telescope position, one can save the guidepixel with @@ guidepix get and set it again by @@ guidepix set. So after interruption one should then point the telescope to the old position, open the shutter and let the guider move the star onto the requested pixel, and then continue with the exposure.

    Limiting magnitudes

    Photometric zero points have not yet been determined for all filters. For the Johnson filters they are:
    U   23.40 +- 0.06
    B   26.40 +- 0.16
    V   26.07 +- 0.05
    R   26.30 +- 0.03
    I   25.16 +- 0.08
    Use the exposure time calculator to determine exposure times.


    The most useful standard MIDAS commands are (for more details use the help command, e.g. help load/image):
    • load/image to load an image into the display. To load an image with cuts 100,200 and scale of 2 you may enter load ima cuts=100,200 sc=2 or shorter @@ ld ima 100,200 2
    • plot/col or plot/row to do plots of columns or rows
    • center/gauss to determine the position of an object
    • comp/ima z = a+b*3*c to do image arithmetic
    The following special utilities are available:
    @@ logsheet        to print observation logsheet(s) 
    @@ dark            to take a series of darks
    @@ domeflat        to take a series of domeflats
    @@ autofocus       to take a focus series
    @@ focus           to evaluate a focus series
    @@ meter           to take a test exposure and measure the flux in it
    @@ standard        to take a series of a standard star field centered on all 4 CCDS
    @@ center          to center an object on one of the CCDs
    @@ expose          to take exposures (+dithering, offsetting)
    @@ gexpose         to take exposures (+dithering, offsetting) with guider in automatic
    @@ guidepix        to get or set the guidepixel
    @@ seeing          to measure seeing on frames
    @@ offset	   to offset the telescope 
    @@ postel	   simple catalogue routine
    @@ shutter         to open/close shutter manually
    @@ lload           to load 4 frames into display. Note that the cursor works only in CCD 1 !     
    @@ zoom 	   to zoom the displayed image around the cursor position
    @@ prepflat        to prepare flats
    @@ fcor            to do flatfield correction
    @@ indisk          to read fits files from disk and convert them to MIDAS format
    @@ intape          to read fits files from tape and convert them to MIDAS format
    Detailed help information is given when entering help as first parameter in a command, eg. @@ seeing help. A list of all available special commands is obtained with @@ laica

    The following commands are useful short forms of frequently used MIDAS commands:

    • cg : center/gauss
    • cco : clear/chan over
    • stc : stat/cursor
    • rk keyname: read/key keyname
    • wk keyname: write/key keyname
    • rd read/desc
    • ld ima cutlow,cuthigh scalefactor
    show/comm gives you an overview of all user defined commands

    Some of the laica commands produce sound output which is very helpful. If you do not get sound ask the local staff or follow the advise given here.

    Treating LAICA data

    LAICA data are more difficult to deal with than those of many other instruments. They have to be calibrated
    • astrometrically due to the distortion of the corrector which amounts up to 20 arcsec in the corners.
    • photometrically since LAICA uses 4 CCDs each with its own wavelength dependent quantum efficiency and each CCD is divided electrically into 4 quadrants, each with its own amplifier. Care has been taken to setup the CCDs as equal as possible. If high photometric accuracy on the order of 5 % or less is required, suitable calibration data have to be taken. If SDSS data exist for the field studied, a procedure described below can be used.
    In the following we describe in some detail procedures which have been used successfully to reduce LAICA data.

    Bias subtraction, flat fielding

    The program @@ prepflat prepares flats from a set of dark0 and flat frames (domeflats or skyflats). It determines the bias level for the frames it uses from the overscan area and computes a median average over several flat exposures which is the flat field. The flats are normalized to quadrant 1 in CCD 1. Example: your file root is jan12, frames 1-3 are dark0 frames, and frames 4-6 are the flats in filter V. Then
    @@ prepflat jan12 4,6 1,3 flatV12 dark12
    will average the dark bias corrected files jan120001-jan120003, save the result as dark12_1 to dark12_4 and subtract these darks from the bias corrected flats, normalize and median average them. The result will be stored as flatV12_1 to flatV12_4. An example of a flat field is shown here.

    The program @@ fcor can be used for flat field correction. It determines the bias from the overscan and corrects for it, subtracts the dark and divides by the flat field. It also checks that the filters in flat and science frames are identical.
    Example: your file root is jan12, you have prepared all your flats and darks, and you have 34 science frames starting at file #7. Then
    @@ fcor jan12 7,40 flatV12 dark12 cor12
    will correct the files jan120007_n to jan120041_n with the flats flat12V_n and dark_n and write the output to files cor120007_n to cor120041_n where n = 1 to 4.

    Astrometric correction

    The distortion amounts up to 20 arcsec in the corners of the LAICA field. This effect is determined and corrected for by a full astrometric solution for each image. First step is to download an astrometric catalogue preferrably the COSMOS sky survey. Download the catalog as ascii file, do not delete the header.

    Second step is to find the x/y positions of the astrometric standards on the CCDs. To this end the coordinates of the standards have to be projected onto a plane (generalized coordinates) and the distortion of the corrector applied. This gives coarse positions of the standards on the CCDs in a linear approximation of the WCS, offsetted by the pointing error of the telescope (the coords of the field center are read from the keywords of the data files). Let us assume that the ascii output file of the COSMOS data is 60942, and you want to treat the (flatfield corrected) data files 30-45. This is done with the command
    @@ prepastro cor12 30,45 60942
    This will first load image cor120030_1, prompt for a correction of the low/high cuts in the display, overload the coarse positions of the standards. The display looks like this. The stars are numbered according to brightness to facilitate identification. You then have to select one star, enter its number, its coarse position is marked yellow and then click on it. The program determines a coordinate offset from this which is applied to all frames of the same pointing. The result is a linear WCS approximation. The program loops through all files, in the example 30-45. This step takes about 15 seconds per pointing and is done quickly even for a large number of frames.

    Third step is to compute the astrometric solution. SExtractor is used to find objetcs on the frames. The stars for which a match in linear WCS position and cataloge is achieved within certain tolerance are identified, an astrometric solution of 2.nd order calculated, stars for which the difference in catalogued and astrometric solution is larger than 1 arcsec discarded and a 3.rd order fit calculated. A typical result of this is shown here; the lengths of the arrows indicate the positions of the stars if there were no distortion. A histogram of the astrometrical errors here. Note that this histogram reflects the errors in the COSMOS data, too. Astrometric errors in the finally rebinned files are on the order of 0.03 arcsec as shown by this histogram of the differences in positions of medium bright stars on 2 frames. Computation of the astrometric solution is time consuming and done in batch mode
    @@ compastro cor12 32,44 60942
    To check the astrometry the program outputs a table file astro.tbl with the most important info. The astrometry is of the polynomial type (RA=x0+A1*x+B1*y+A2*x**2+A3*xy+A4*y**2...) and stored as descriptors to the files.

    Finally the files are rebinned to RA/DEC and stacked. This too is done in batch mode. Example:
    crea/icat cor12*bdf
    creates a catalog of files to process, in our example all files cor12*bdf with *=0030-0045. To rebin these to a frame with 16000x16000 pixels with RA/DEC = 22.65/41.00 degrees at pixel x/y=1/1 at a step size of 0.224 arcsec/pixel
    @@ rebstack Gave ? ? 0,2 16000,16000,22.65,41.00,0.224
    The program creates rebinned files (prefix reb) and stacks them to the output file Gave. Several stacking modes are available, such as average, median, and kappa/sigma clipping. (The meaning of all parameters is given in the help @@ rebstack help).

    Photometric correction

    If SDSS data exist for the field one can use these to correct photometry. Example:
    crea/icat rebcor12*.bdf creates a catalog of rebinned files. The instrumental magnitudes are compared to sdss data and corrected by
    @@ photcorr T sdss g 0 where g is the pass band. photcorr corrects the original flatfielded files, which now have the first character K, eg. Kor120030_1 and so on. These must be rebinned and stacked
    crea/icat K*bdf
    @@ rebstack T Gave ? ? 0,1 16000,16000,22.65,41.00,0.224

    Saving the data

    Since each frame has 142 Mbytes, one clear night will produce around 10 Gbytes. Save your data on DAT. To avoid hazzle with full DATs during observations, use a new DDS3 tape for each night. To save the data as genuine FITS-files use the CA-script fitscopyx and to list the DAT use ccdlistx . To save the data on DAT in tar-format rewind the tape mt rew and copy the data tar cv * . Be careful not to overwrite data; it is best to use a new DAT for each save! List the tape with mt rew then tar tv > dat.list

    Current Status (March 2006)

    LAICA is up and alive! The setup of the CCDs and the software, especially of the guider, has been improved.

    The LAICA team

  • construction + mechanics: Bellemann, Benesch, Baumeister
  • electronics: Ehret, Grimm, Klein
  • CCD: Marien
  • software: Briegel
  • PI: Fried



    The following filters are standard LAICA filters; if one of these is used, any focus offset is automatically corrected for. The foci are approximate, determined in poor seeing (2-3")
    #   name       glasses            focus
    1     U    UG1/1+BG39/2            29.7
    2     B    BG37/1+BG39/2           29.6
    3     V    BG18/1+GG495/2          29.6
    4     R    OG570/2+Calflex X       29.3
    5     I    RG780/3                 29.75
    6     B2   BG12/1+BG39/1+WG295/1   29.7
    7     black is beautiful
    8     u'   UG11/1+BG38/1+coating   29.6
    9     g'   GG440/2+BG38/3+coating  30.3
    10    r'   OG550/4+coating         29.9
    11    i'   RG695/4                 29.9
    12    z    RG830/3                 29.6
    Transmission curves for the Johnson-like filters :

    Transmission curves for the SDSS filters :

    Transmission data as ASCII files: John_U John_B John_B2 John_V John_R John_I SDSS_u SDSS_g SDSS_r SDSS_i SDSS_z

    Install a new filter

    To install a new filter (to be done by the local staff only!), open the filter magazine's back door, take off the aluminum plate, take out the filter holder, put in the filters for the science and guider CCDS, and put the filter holder back again, close the filter magazine.
    Determine the focus for the new filter, calculate the offset to filter R (focus new filter - focus R) and edit the filter list /CalarAlto/etc/laica.xml.

    Shutter uniformity

    The shutter is of the focal plane type, like in an SLR camera (the german Schlitzverschluss describes it very well). Non-uniformities as derived from flats are on the order of 0.1% for exposure times down to 0.3 sec. Click here for an illustration of shutter effects (shown here are the ratios of flats with different exposure times).

    The CCDs

    The CCDs are of the 485 type delivered by a company which in February 2002 was called BAE (formerly Lockheed Martin). The serial numbers of the CCDS are M1=1536, M2=4008,M3=486BIDB79,M4=4034. The quantum efficiencies as measured by the manufacturer are given here for M1, M2, M3 and M4. Great care has been taken to set the DC offset and sensitivity (electrons/ADU) equal for all quadrants within each CCD. M3 has been set to give the same signal in R than the other CCDs. The basic parameters as measured in march 2006 are listed below. RON means read out noise in electrons, sens the sensitivity (electrons/ADU). CCD1 is from a different charge and has a higher read out noise. The numbering scheme for the quadrants is the same as for the CCDs themselves.
    LAICA CCD Parameters measured in march 2006
    Sequence ccd        quad       ron        gain
     -------- ---------- ---------- ---------- ----------
            1         +1         +1      13.08     +1.558
            2         +1         +2      14.65     +1.587
            3         +1         +3      11.79     +1.499
            4         +1         +4      12.41     +1.596
            5         +2         +1       6.04     +1.530
            6         +2         +2       6.37     +1.519
            7         +2         +3       7.54     +1.507
            8         +2         +4       6.40     +1.592
            9         +3         +1       4.15     +1.242
           10         +3         +2       5.30     +1.190
           11         +3         +3       4.14     +1.203
           12         +3         +4       4.53     +1.258
           13         +4         +1       7.14     +1.597
           14         +4         +2       6.17     +1.627
           15         +4         +3       7.43     +1.577
           16         +4         +4       5.31     +1.572
     -------- ---------- ---------- ---------- ----------
    RON  in electrons     sens in ADU/electron
    One can easily measure the CCD parameters using @@ ccdpars. This command needs 2 dark0 frames and 2 flats with the same filter and exposure time; @@ sens is a convenient way to get the 2 darks and 2 flats. The CCD parameters are then calculated by eg.
    @@ ccdpars flat1 flat2 dark1 dark2
    For each quadrant the CCD parameters are evaluated using the formula given by Janesick
                   (mean(flat1)+mean(flat2)) - (mean(bias1)+mean(bias2))
           sens = -------------------------------------------------------   [el/ADU]
                          sigma(flat0)**2 - sigma(bias0)**2
                   sens * sigma(bias0)
           RON  = ----------------------  [el]
    where flat0=flat2-flat1 and bias0 = bias2-bias1. The parameters are stored in a table and an ASCII file sens.


    Coma arises from a tilted primary mirror and/or decentering of the telescope. The Calar Alto personnel checks the alignment of the telescope regularly to ensure high image quality.

    The 3-lens corrector causes noticeable pincushion distortion, i.e. a star appears in the image farther away from the optical axis (which is in between the CCDs). The distortion is well described by

    dist = 10**(-4)*r**2

    where r is the distance from the optical center in mm, and the distortion dist is measured in %.

    Trouble shooting

    The sky is cloudy

    • go to bed

    The midas receiver does not convert the files

    • midas is not working on the proper directory

    No sound

    Some LAICA MIDAS commands are producing sound output. If you do not get sound then either the volume of the speaker may be turned off, or the speaker is not connected, or the headphones are not selected as output. In this case, start the audiotool and select headphones as output (play button). If this does not help, ask the local staff.

    Connection to read out electronics is shaky

    • this is probably caused by poor fiber connection to the read out electronics. Ask local staff to use other fibers.
    • for a hard reset it may be necessary to turn the read out electronics off and on again. To do so, start a web browser, connect to Login as user, ask local staff for the password. Turn electronics off/on in the GUI that appears.

    Installation Notes

    Mounting LAICA to the frontring:

    See the following foto. A schematical drawing is shown here , and the arrangement of the CCDs as seen looking onto the dewar is sketched here , as seen from the sky here .

    The front ring must not be tilted! If the focus is 28.5 then the individual foci must be at the same value, i.e.
    FOK E = 28.5
    FOK W = 28.5
    FOK N = 28.5
    FOK S = 28.5
    These values have been determined in October 2003. These values must be checked after installation of the frontring. To check the actual values enter
    Wahl1 -> FOKSW
    Wahl1 -> FOKNE
    To change these values enter
    @KIPPSW value CNTRL A -- tilt at SW axis
    @KIPPNS value CNTRL A -- tilt at NS axis


    To verify the pointing, select a PPM star, use @@ center 1 to move this star on CCD 1. Load image of CCD_1 into display. If the star is not in the center, use @@ offset 2100,2048 to measure the offset to the center. Turn off the main drives, correct offset with
    by subtracting the measured RA offset but adding the measured DEC offset to the values which are stored in KORPAR. Start the drives. Note that these values change each time the telescope computer is turned off!!! Parameters in October 2003: -256 / -89

    Communication with filter/shutter electronics

    only for staff on Calar Alto!!
    telnet flotest 951
    ?S status
    ?E010 exposure 1 second
    ?F3 put in filter3
    For a list of commands see the little laica manual by H.Unser (should be in the LAICA closet on the second floor).