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News:

The repair of the LAICA mosaic was successful! The broken CCD and window were replaced. The new CCD is working well.

We have now included an exposure time calculator in the manual.

Instrument Status:

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Overview:

LAICA is the new Large Area Imager for Calar Alto. The project started in spring 1999. The aim was to build a camera with 8192 by 8192 pixels (67 Megapixels). LAICA is installed at the Prime Focus of the 3.5m telescope on Calar Alto using the 3-lens corrector K3. The basic facts are summarized here:
 
 
LAICA in a Nutshell
Telescope  3.5m Calar Alto
Telescope focus  Prime Focus K3 corrector 
F Ratio  f/3.9
Field of view  44.36' x 44.36' 
Pixel scale  0.225 arcsec/pixel
Detector  2 x 2 mosaic of 4k x 4k CCDs
Filling factor  100%
Read-out time  < 100 seconds 
Dynamical range  16 bit
Wavelength range  Atmospheric cutoff to 1 micron
Intrinsic image quality  0.3 arcsec
Geometrical distortions  <= 2%
Data format  FITS (with extensions), 140 Mbyte/file

LAICA installed at the prime focus is shown here. The instrument is made up of 3 parts: the CCD array, a filter module and a shutter.

The CCD Array:

LAICA uses 4 CCDs with 4096*4096 pixels each with a pixelsize of 15 microns manufactured by BAE systems (formerly Lockheed Martin). Since these CCDs are not buttable, we have chosen an arrangement as shown here; the dimensions in arcseconds are given here The spacing between the CCDs is equal to the size of a single CCD minus an overlap of about 100 arcsecs which may serve for astrometric and photometric calibration purposes.

A single exposure thus will not yield a contiguous field, which is probably not required for many applications. If a contiguous field is required, a series of 4 exposures has to be taken to fill the gaps between the CCDs. Click here for an illustration. The advantage of this arrangement is that it makes full use of the sensitive area: the filling factor is 100%. A further advantage is that 4 single small filters can be used (instead of a single large one) which are much easier available and cheaper. The main disadvantage of this arrangement is enhancement of image distortion effects; image degradation in the corners of the field should be minimal due to the high optical quality of the corrector optics.
 

The main features of the CCDs are


 

The Filter Module:

The filter module is similar to a slide projector: each set of 6 filters (4 for the science CCDs plus 2 for the guider CCDs) is mounted in a filter holder; 20 filter holders can be stored in the magazine. The selected filter is moved from the magazine into the beam by a grabber.

The Filters:

Two filter sets will be available after commissioning, one standard UBVRI set plus an additional broad B, and another similar to the SDSS filters.  Click for transmission curves of Johnson and SDSS filters.
 
 
  <
U_Johnson  3500 520  
B_Johnson  4200 1400  
V_Johnson 5500 1150  
R_Johnson 6600 1850  
I_Johnson 9000 100  
B2     4300 1480  
u'   SDSS 3500 630  
g'   SDSS 4900 1230  
r'    SDSS 6200 1350  
i'    SDSS 7700 1500  
z'   SDSS 9200 1600  
 
 
 
 
 
 
 
 
 

 

The Shutter:

Tests have shown that inhomogeneities due to the shutter at exposure times as short as 0.5 second are less than 0.1 % over the whole field. This allows to take sky-flats shortly after sunset/before sunrise.
 


Guiding:

The CCD layout also shows 2 smaller CCDs which are used for guiding. These CCDs are operated in the frame transfer mode, so there is no special shutter required for the guider CCDs.


Current status:

LAICA has been tested - for the first time with all CCDs working properly - on the telescope from October 2003, 24 to 27. Clouds prevented tests with star light. The CCD array looks very good, tests of linearity, dark current, shutter homogeneity etc all gave excellent results. LAICA has been used in december 2003, and worked very well, including the auto guider. The Coma has been removed by alignment of the main telescope mirror. Until summer, we will prepare timings for fast read out, as well as a special timing for low blooming. We will also improve the cooling system.

The LAICA Team:

  • construction + mechanics: Rohloff, Baumeister, Benesch
  • electronics: Grimm, Klein, Unser
  • CCDs: Marien
  • software: Zimmermann, Briegel
  • PI: Fried

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    Note: LAICA is neither LAIKA nor Leica!

    Comments of a theoretician: Projects like this one always get delayed. But it does not matter anyway.


    responsible for this page: J.W. Fried