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This page provides the most recent encircled energy values for ACS, as the values published by Sirianni et al. (2005) are no longer valid and have been updated via several publications. The encircled energy values are used to compute the aperture corrections required to account for flux falling outside an aperture of radius R, where R is less than the "infinite" aperture. For the HRC and WFC, the infinite aperture radius is defined to be 5.5". For SBC, the infinite aperture radius is defined to be 4". The HRC and WFC values used to generate the figures below were dervied in Bohlin (2016) and the values for SBC were derived in ACS ISR 2016-05. Each dataset is available for download at the bottom of this page.

Interactive Encircled Energy Plots

Determine the value for a specific radius

Hover over the datapoint. This will display the coordinates (radius, encircled) and the filter name for the curve the cursor covers. Note that we only provide values for radii that were measured in the analysis, no interpolation has been done.  

Select a single filter 

Double click the filter name in the legend. This will toggle off all other filters except the one that has been double clicked allowing you to investigate whichever filter you desire.

  • To undo this operation, double click anywhere on the legend.
  • To view other filters for comparions, single click the desired filter in the legend to toggle it on

Zoom in

Determine the area you wish to examine, then click and hold to draw a rectangle around the desired region.

  • To undo this operation, double click anywhere on the plot and it will return to its default state.

Encircled Energy Downloads

Last Updated: 06/02/2023


HST Help Desk 

Please contact the HST Help Desk with any questions.