BUSCA technical data

BUSCA data:
Number of dichroic plates 3
Detectors 3x CCD485 Lockheed Martin,  4096 x 4096 pixels with 15mue x 15mue, frontside devices, 
1 CCD485 backside thinned (in the uv channel). 
Number of pixels ca. 67 Mill. (4x 16.8 Mill.), ca. 16.8 Mill. total with 2x2 binning
Field of view 12 arcmin x 12 arcmin
Pixel size 0.176 arcsec (0.35arcsec with 2x2 binning, standard at typical seeing conditions)
CCD controller MPIA design, 4 channels maximum
CCD read out four color channels simultaneously
Read out time ca. 1:30min with 2x2 binning
Shutter: Type "Bonn Shutter", two blade, stepper motor driven
Shutter: Min. exposure time < 10ms
Shutter: Photometric performance Exposure homogeneity >99% at 100ms exposure time
Guider FOV 5.6 arcmin x 4.2 arcmin
Guider field position fixed, 8 arcmin north of camera field center
Data storage/format one FITS file for each of the four CCD frames 


Channel data and basic filters set:

channel a b c d
wavelength < 430 nm 430nm - 540nm 540nm - 730nm > 730nm
CCD 4k x 4k (thinned) 4k x 4k 4k x 4k 4k x 4k
gain [e-/ADU] 2.02 1.08 1.34 1.25
linearity [ADU] 40000 50000 52000 50000
read out noise [e-] 9.3 2.66 3.55 4.17
filter pos 1 UV_B (WG 280) B_B (WG 280) R_B (WG 280) NIR_B (WG 280)
filter pos 2 Strömgren v H beta (narrow) free free
filter pos 3 Strömgren u Strömgren b Strömgren y free
filter pos 4 free H beta (wide) free Cousins I

The values for the gain and readout noise are measured with the CDS-Gain of 20. The real values for channel b which has normally the CDS-Gain of 50 you have to divide these values by 2.5.

The use of additional existing filters from the observatory (if to be used simultaneously!) is limited to those with identical optical path lengths. It should also be kept in mind, that the 4K x 4K CCDs need large filters (diam.: 109 mm and thick.: 15 mm) to avoid vignetting. If a reduced field of view is acceptable, smaller filters could be inserted (Calar Alto Observatory disposes only of 5 adapters for filters with a diameter of 50 mm and 5 adapters for filters with a diameter of 70 mm). A typical 50 mm filter reduces the FOV to about 6 arcmin.

VERY IMPORTANT:   The optical path lengths through simultaneously used filters have to be identical, i.e. they should have the same thickness. The CCD's can not be focussed individually.

The Four BUSCA wavebands. They are named - from left to right - uv, b, r, nir. Indicated are positons and widths of standard line, intermediate and broadband filters. Click here to get the ascii table of the Beam Splitter QE . Effective tansmission of the available Strömgren and broad band filters (CCD QE not included). Now, H beta (wide) and H beta (narrow) are also available. (To get the ascii table click on the picture.)