Telescope and Focus Choice

CCD imaging at CTIO is offered on the 4-m telescope with Mosaic Imager, the 1.5-m at either F/7.5 or F/13.5 foci, at the 0.9-m F/13.5, and on the YALO 1.0-m telescope using the dual IR-optical Imager ANDICAM. The latter is especually suited to synoptic programs. Note: This manual describes only the Cass focus systems offered at the 0.9-m and 1.5-m. We no longer offer Cass focus CCD imaging on the Blanco 4-m telescope. If you are lost, try going to "Optical Instruments"

At the 1.5-m we offer a choice of two foci, F/7.5 and F/13.5. The F/13.5 has smaller field and finer pixel scale (8 arcmin, 0.24 arcsec/pixel) compared to F/7.5 (15 arcmin, 0.44 arcsec/pixel). However, the telescope has much better image quality at F/13.5, and is capable of producing 0.7 arcsec images, compared to F/7.5 where the image floor is around 1.1 arcsec. Thus, unless you REALLY need the larger field, F/13.5 is the focus to choose.

At both the 0.9-m and 1.5-m telescope we use a SITe 2048 CCD for CCD imaging. Normally this will be SITe 2048 #3 at the 0.9-m and SITE 2048 #6 at the 1.5-m At CTIO all CCDs are operated using ARCON controllers. These controllers consist of a small box bolted to the dewar, which contains all the electronics needed to operate that particular CCD, followed by a fiber-optic link to a TRAM BOX "Silicon City" which sits beside a SUN 10/41 computer to which it is connected. The astronomer operates the Arcon from within an IRAF-based integrated data acquisition-data reduction environment. You will find a much more powerful SUN available for data reduction. A real-time monitor, which displays the CCD image as it is read out, is attached to the TRAM box, while status and image statistics are displayed in a status window on the Sun screen. Apart from gains in reliability expected to follow from the affixing of the CCD dewar to its electronics, the use of fiber-optics, and the great attention that has been paid to mechanical and electronic construction, there are a number of performance gains:

  • quad channel readout for CCD's with multi-amplifiers
  • unsigned 16 bit data (0-65535) allows greater dynamic range
  • dc coupled preamp means no memory of image in overscan
  • real time display with saturated pixels in red
  • direct data interface to SUN/IRAF
  • faster readout in single channel mode for most CCD's
  • Arcon 3.2, Tektronix 1024 #2
  • Arcon 3.3, Tektronix 2048 #3 (dedicated to the 0.9m telescope)
  • Arcon 3.5, Loral 3K #1 (4m spectroscopy)
  • Arcon 3.6, SITe 2048 #6
  • Arcon 3.9, Loral 1K (1.5m spectroscopy)
  • Arcon 3.17, SITe 2K #5 (Schmidt)

Detector characteristics are summarized in section IV below. We will schedule the CCD that we think is the optimum one for your program, taking into consideration the device specifically requested on the Visitor Support Questionnaire and the proviso that in cases of conflict the larger telescope has priority. As indicated above, some CCDs (eg both Lorals) are in specialized dewars), while others are dedicated to a particular telescope (0.9m, Schmidt).