How to Use this Handbook

This handbook was created to help users process and analyze data from the Advanced Camera for Surveys (ACS) which was installed on-board the Hubble Space Telescope (HST) during the 2002 servicing mission (SM3B). It is presented as an independent and self-contained document, designed for users familiar with HST data but new to ACS. Users who wish to find more general data analysis information, including instructions for retrieving data from the HST Archive, a description of HST file formats, and details regarding data analysis software supported by STScI, are referred to a companion volume, the Introduction to HST Data Handbooks.

For information about geometric distortion and drizzling ACS data, please refer to the DrizzlePac website.

Since many of the instrument characteristics may be revised over a short time frame, readers are advised to consult the ACS website for the latest information regarding ACS performance and calibration.

ACS Spectropolarimetry

Imaging spectropolarimetry is now offered for ACS in Cycle 31+. The ACS polarizers can be used in conjunction with the G800L grism to provide low spectral resolving power (R~100 @ 8000Å) imaging spectropolarimetry from ~5500Å – 8000Å. This mode is still being calibrated during Cycle 30. Therefore, prior to proposing, potential observers should contact the Help Desk to discuss their specific goals and the current status of the mode. More details are discussed in Chapter 5.3.


The ACS team has produced a new python package (Slitlessutils) to extract and simulate slitless spectroscopy data.  For spectral extraction, the package offers two techniques: the single-orient extraction, which employs a very similar algorithm to HSTaXe, while the multi-orient extraction enables the linear-reconstruction techniques developed by Ryan, Casertano, & Pirzkal (2018).  Although this package is under active development, the current stable versions are on GitHubwith more information available at the read the docs website

Astroconda is not supported by STScI as of 1st February 2023. The Space Telescope Science Institute has released "stenv" to supersede Astroconda for its software distribution. stenv provides a common environment for both the Hubble Space Telescope (HST) and the James Webb Space Telescope (JWST) pipelines and includes most of the packages in Astroconda. Instructions for installing and using stenv can be found at Questions can be directed to the HST Help Desk Portal.

STSDAS and PyRAF are not supported by STScI. The last software to use STSDAS/PyRAF was aXe, a slitless spectroscopy software, and it is now replaced by HSTaXe, a PyRAF independent follow-up to aXe, available at . All other data processing described herein now uses Python.