Click here for the manual !
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:
Show News (public)
Add status (private)
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
- read out noise of about 6 electrons
- excellent cosmetics
- full well capacity of 100000 electrons
- high quantum efficiency. Find here the curves for the detectors M1, M2, M3 and M4.
- fast read out of about 70 seconds
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 |
|
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| z' SDSS |
9200 |
1600 |
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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
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: Astronoy Department
