Computing Exposure Times with the IRAF Task CCDTIME


Using this form investigators can estimate the integration time, magnitude, or signal-to-noise ratio (SNR) for a stellar observation for a given telescope, CCD or IR imager, and filter combination at specified seeing/airmass/sky conditions at CTIO, SOAR, or KPNO. Simply fill in the appropriate information below and press the Execute button. Database files contain the telescope, filter, and detector information necessary to compute the quantities for CTIO, SOAR, and KPNO, using the IRAF task ccdtime. The Gemini Observatory maintains calculators for its facility instruments.

CCDTIME is intended to provide an approximate exposure guide; the treatment of sky brightness is based upon Walker (1987 NOAO Newsletter No. 10, 16); see also discussion in Elias (NOAO Newsletter No. 37, 29).

In the form below, leave either the integration time, the magnitude, or the signal-to-noise ratio field set to INDEF, or leave it blank, to compute this value based on the other parameters. Rough estimates are available for the CTIO Mosaic imager using data from the KPNO Mosaic imager. No calibration data is available yet for the WIYN Mini-Mosaic but the calibration data for the WIYN CCD Imager should give comparable estimates. Investigators may select instruments for one or both observatories using the same parameter input.

Additional information about the imaging instruments at these observatories can be found at the Web sites for KPNO, CTIO, and SOAR.

An Excel spreadsheet for estimating DECam exposures can be found on the CTIO DECam page.

Please use the CTIO Infrared Imager Exposure Time Calculator for CT-4m observations with ISPI.

Information for estimating exposure times for CT-1.3m telescope can be found on the OSU Andicam Page.


Choose an instrument from a list below. If instruments are chosen from multiple lists then the output will contain information for all setups using the same parameters chosen below. Those instruments marked in the list with an "*" are no longer offered, but are provided here for comparison purposes for observers with continuing programs using other instruments.


CTIO instrument:
SOAR instrument:
KPNO instrument:


Set one of the three parameters below to INDEF or leave it blank to compute its value based on the other input parameters.

Integration time in seconds:      Magnitude:      Signal-to-noise ratio:


Specify the remaining parameters - note that the "CCD summing factor" parameter will be reset to "1 x 1" the KPNO CCD Mosaic Imager.

Seeing (arcsecs):      Airmass:      CCD summing factor:
(see note above)

Lunar Phase (0-14 days from new moon, 0 = new, 14 = full):   


KPNO and CTIO also maintain additional Web tools for helping investigators to identify imaging or spectroscopic needs and exposure times. KPNO has two tools at http://www.noao.edu/kpno/imaging/imaging.html (identify a telescope/instrument configuration from input requirements) and at http://www.noao.edu/kpno/spectroscopy/spect.html (predict a telescope/ spectrograph combination based on input parameters). CTIO supports exposure time calculators for many of their optical spectrographs - see http://www.ctio.noao.edu/spectrographs/spectrographs.html.
webmaster@noao.edu
22 Mar 2013