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ACS Detectors

The Advanced Camera for Surveys (ACS) employs two fundamentally different types of detectors: Charge-coupled device (CCD) for use from the near-UV to the near-IR, and a Multi-Anode Microchannel Array detector (MAMA) for use in the ultraviolet. The CCD and the MAMA detectors are used in different ways and impose their own unique limitations on the feasibility of observations performed with them. The ACS is a third generation HST instrument and includes three channels whose specifications are listed in the table below:

  • The Wide Field Channel (WFC)
  • The High Resolution Channel (HRC)
  • The Solar Blind Channel (SBC)

The ACS optical design incorporates two main optical channels: one for the WFC, and one which is shared by the HRC and SBC.

Instrument Characterization and Documentation

For a high-level description of the ACS detectors please refer to Chapter 3 in the ACS Instrument Handbook (ACS IHB) or Chapter 1 in the ACS Data Handbook (ACS DHB). For an in-depth description of the ACS detectors please refer to the following chapters of the ACS IHB:

WFC and HRC CCD Detectors

SBC MAMA Detector

Quick Reference Table

  WFC HRC (Inoperable) SBC
Field of View 202" x 202" 29" x 26" 34.6" x 30.8"

Plate Scale

~0.05"/pixel x 0.05"/pixel ~0.028"/pixel x 0.025"/pixel ~0.034"/pixel x 0.030"/pixel
Pixel Size 15 x 15 μm2 21 x 21 μm2 25 x 25 μm2
Image Format 2 x 2048 x 4096 pixels2 1024 x 1024 pixels2 1024 x 1024 pixels2
Spectral Format ~3500 Å to 11000 Å ~1700 Å to 11000 Å ~1150 Å to 1700 Å
Detector Type

SITEe thinned backside illuminated CCD, anti-reflection coated, multiphase pinned

SITEe thinned backside illuminated CCD, anti-reflection coated, multiphase pinned

CsI photocathode deposited on a microchannel plate with MAMA readout

Detector Efficiency

~ 77% at 4000 Å

~83% at 6000 Å

~67% at 8000 Å

~33% at 2500 Å

~69% at 6000 Å

~53% at 8000 Å

~19.2% at 1216 Å
Peak Efficiency 48% at ~7000Å 29% at ~6500 Å 7.5% at 1250 Å
Read Noise 3.7 e- to 5.2 e- 4.7 e- 0 counts
Dark Current 0.019 es-1 pixel-1 0.0058 es-1 pixel-1 8.11 x 10-6 counts s-1 pixel-1 when temperature is less than 25ºC
Full Well 84700 e- 155000 e-

Detector limit: 200,000 counts s-1

Pixel limit: 22 counts s-1 pixel-1

Gain 0.5, 1.0, 1.4, and 2.0 e- DN-1 1.0, 2.0, 4.0, and 8.0 e- DN-1 N/A
Operating Temperature -81ºC -80ºC 20 - 30ºC


LAST UPDATED: 08/27/2021

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