U-band image of the Moon acquired on the AAT on 2 Feb 2001Copyright AAO.
U-band image of the Moon acquired on the AAT on 2 Feb 2001 by Chris Tinney, Fraser Clarke and Gordon Schafer.  The image was 0.1s long and acquired about 40 minutes after sunset.  Copyright AAO.)
The Wide Field Imager & 
Prime Focus Unit at the AAT

Useful WFI links
AAO Home PageRSAA Home PageUniversity of Melbourne School of PhysicsAuspace Limited


What's New

CASU Data Toolkit Notes (January 2005).

Notes on the use of the CASU Imaging Toolkit to process WFI data at the AAO in Epping have been added to the WFI Data Reduction Guide page.

AAO WFI/PFU Pages completely revised (Feburary 2002).

New documentaion pages include
WFI Cookbook - with complete description of the use of WFI for imaging at the AAT
WFI Performance - a summary of measured WFI & PFU performace at the AAT
WFI proposers to the AAT should consult the new WFI Performance  page, when preparing their proposals for semesters from 2002B onwards.


The Wide Field Imager (WFI) is a joint project between the AAO,  RSAA(otherwise known as Mt Stromlo) and the University of Melbourne to construct an 8Kx8K CCD imaging mosaic for use at the 3.9m AAT and the SSO 1m.

The Prime Focus Unit (PFU) is an AAO project to provide upgraded facilities at the f/3.3 AAT prime focus for the mounting of CCD detectors. In particular, it was required on order to mount the WFI and the AAT, and to provide filter wheel and shutter facilities.

The Wide Field Imager

WFI provides a focal plane CCD detector system with a size of 123 by 123 mm, 8192 by 8192 pixels, made up of a 4 x 2 array of 2048 x 4096 pixel thinned, back-illuminated CCDs, to be used on both the Anglo Australian and ANU 40inch Telescopes. The output of the system is pixel data in the form of multi-extension FITS files written on an archiving medium which is part of the system, and/or transported to a device of the user's choice over a Local Area Network, or fed into an automated archiving and reduction pipeline where available.
Top and side-on views of the WFI dewar showing the eight CCDs in place

At the centre of the system is a 123 x 123 mm focal plane mosaic of eight three side buttable 2048 x 4096 15 micron pixel CCDs which AAO and MSSSO procured a partnership of astronomical institutions who funded the development of thedevices at Lincoln Labs in the USA.

The focal plane is housed in an evacuated vessel (the "dewar") and is cooled to 183 K by the use of liquid nitrogen refrigeration.

The dewar fits onto the PFU exposure controller at the AAT Prime Focus. PFU allows astronomers to remotely control up to six 165mm x 165mm filters, and to expose WFI using a 165mm x 165mm twin-travelling-blade shutter

Autoguiding can be done using of one of eight small guide CCDs located on the focal plane next to the scientific detectors. Two San Diego State University second generation CCD controllers are mounted on the dewar to read out the CCDs and transfer the data over fibre optic links to the data acquisition computer system.

The control and data acquisition computer systems consist of two Sun workstations, which handle  the data stream from the CCD controller sfor display, storage and archiving in 60s per exposure.


The following organisations have been involved in the WFI project:
  • RSAA:  RSAA provided the overall project management, CCD expertise, four 2048 x 4096 CCD chips and the MSSSO's workshop infrastructure.
  • AAO: the Anglo Australian Observatory provided the other four CCDs, and built PFU to accomodate WFI at the AAT.
  • University of Melbourne: The astrophysics group assisted in developing the scientific requirements for the Project.
  • Auspace Ltd: Auspace provided project management, quality assurance and mechanical design to the project.
  • Construction of WFI was made possible by a REIF (Research Infrastructure - Equiment and Facilities) grant from the Australian Research Council.


    The major contractors involved in the WFI project was GL Scientific, who manufactured the focal plane and assembled it into the dewar built at RSAA: Building the focal plane, assembly of instrument and testing.

    Prime Focus Unit

    PFU provides an automated facility for the use of CCDs at the AAT's f/3.3 prime focus. The diagram below shows a detail of the PFU design, and a sample image obtained with a single MITLL CCD - WFI contains eight of these CCDs.



    The following documentation for WFI and PFU is available at the AAO (links in these pages also provide access to WFI documentation at other sites).

    This page maintained by Chris Tinney
    Last updated 22 February 2002.