Acquisition Camera Observing Strategies and Instrument Limitations

Basic Calibration Issues:

• There is strong fringing in the I band and less noticeable one in the R band. Users that need good flat-fielding should be aware that blank-sky flats of sufficient exposure are needed for correction, specially for long exposures in bright lunar phase. The I-band fringe flats will be provided as part of the baseline calibration set. For other bands, they should be asked as special calibrations and included in the requested exposure time. 
• Darks: we are currently evaluating the behaviour of the dark current as a function of (a) the exposure time; (b) small variations (~1 ^o C) of the detector temperature; (c) long term variations on the dark frames 2D structure.  Appropriate dark frames will, in any case, be supplied as part of the baseline calibration set.

Observing modes:

• Although the detector is a frame transfer device, please note that operating in frame transfer mode (zero time between exposures) is not supported. The minimum overhead between full frame images is 1.7 seconds (the CCD readout time). 
• Binning the CCD is available for 2x2 pix mode only (pixel size = 0.24 arcsec)
• Windowing readout is also available, for any window size. However, we recommend a minimum size of 100x100 pixels. 
• The fastest possible readout times for several configurations are shown in the table below. Proposals that require this rapid readout time should clearly express it on the experimental design, taking into account the instrument restrictions also listed in this page. Otherwise, proposers should assume there will be a 7-9 seconds overhead between images.

Instrument restrictions:

• Proposals that require dithering should consider that the overhead between images in this mode is currently 7-9 seconds for dithers smaller than 5 arcsec, and longer than that for larger offsets.
• Proposals that require rapid cycling between the filters (for example, sequences of short integration time images taken through  BVRI filters in succession) also should consider a 7-9 seconds overhead between images.
• For observations without dithering, please be sure that there isn't any bright star in the image field, that can heavily saturate the detector in the requested integration time.  This issue is specially important for long (many hours) series of exposures.