STScI Logo

ACS Exposure Time Calculators (ETCs)

For current ACS ETC runs, please start by using the following link and ignore the older information farther below! Link for current ACS ETC

Ignore information below this point if you want the current ETC. If you want the current ETC, use the link above!

The February 2005 on-orbit tests of ACS instrument performance in two-gyro mode indicate that the exposure time differences between two-gyro mode and three-gyro mode operations are negligible. The existing ACS ETCs are appropriate for either mode, and there is no longer any need to choose between the two modes within the ETCs. If this situation changes, the ACS Team will provide updated information on this web page.

On Monday, April 26, 2004 newer, revised ETCs were released.

The following enhancements are implemented:

1) available but unsupported modes for calibration purposes (e.g. clear-clear) are now allowed to compute

2) newer dark rates values for the WFC and the HRC are in place (WFC: 11.1 e-/pix/hr or 3.08 e-3 e-/px/sec and HRC: 13.4 e-/px/hr or 3.72 e-3 e-/px/sec).

3) a fix was applied to the SBC modes to more accurately calculate the global limit for extended sources greater than the size of the detector.

On September 10, 2003 a revised version of the ETCs for ACS is delivered. This release is primarily focused on usability improvements including better handling of invalid input data and clearer error and warning messages.

Other improvements:

1. This version uses a newer release of the Tomcat web server (4.1.27) and a newer release of the Java Virtual Machine (1.4.2).

2. More complete extraction region tables have been included that support circular regions up to 4 arc seconds in radius containing 100% of the flux.

3. The output pages have been reformatted to improve readability.

The new Exposure Time Calculators linked above were recently developed as part of the Astronomer's Proposal Tool (APT). The links provide access through an interface with the same look-and-feel as the old (CGI) ETCs. We recommend the new APT versions for all users. They have several new features and improvements, as described here. For problems or questions please email