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Team lava

Last updated
15 February 2002 12:28:49

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Printable version

Image Quality vs Field Position : WFC and HRC

PROCEDURE : 00w, 01h, 01w, 02h, 02w

TITLE : Image Quality vs Field Position : WFC and HRC

CATEGORY : Verification/Calibration


The main goal is to characterize the instrumental PSF (encircled energy and FWHM) over the HRC#1 and WFC#4 fields with the RAS/HOMS fiber spots at the default wavelength of 6328 Ang. The optimal focus values of the M1 (HRC) and IM1 (WFC) mirrors for the individual spots and across the entire field will be determined, as well as the inner and outer cylinder positions that optimize the coma correction. The data will simultaneously allow a verification and refinement of the location of the RAS source plate and hence of the fiber spot apertures. This is the preparatory part of the calibration campaign.


Execute the focus and tip-tilt procedures at the beginning of the campaign and iterate until the optimal values have been found. Perform a final pass of the focus SMSs with the best focus values for verification and final measurements. If time permits, repeat all procedures in the middle or end of the campaign to verify the stability of the focus and tip-tilt positions.


Flight build detectors HRC#1 and WFC#4. Since non-science data are acquired, the gain is unimportant; values of 1 e-/DN are used for both detectors with offsets of 0.


The location of the fiber spots on the WFC field is represented schematically in Fig. 1. For the HRC, a separate fiber, A10, can be translated across the FOV. Examples of the undispersed fiber spots acquired in the Dec 2000 BATC campaign (HRC#1, WFC#4) with RAS/HOMS at its default wavelength of 6328 Ang are shown in Figs. 2 and 3.

Similarly, examples from the Jun 2000 BATC campaign of the RAS/HOMS fiber spots dispersed with the G800L grating at 6328 Ang are shown in Figs. 4 and 5.


ACS is integrated in RAS/HOMS and the HeNe lasers turned on. A qualified operator must be inside the clean room to manually adjust the fiber light intensities and the plate micrometers.


The IDL procedures 'qfit' and 'cmfscan' analyze the focus sweeps.

COMMAND MODE : SMS and real time.


As starting points, the focus and corrector mechanism positions are set at the optimal settings determined in the Dec 2000 or early Jan 2001 (WFC only) alignment campaigns. The best December values were refined from those of the June 2000 BATC campaign, including a small correction to the HRC focus from the HRC and SBC Confocality Test performed in Sep 2000 at GSFC. The SMSs will later perform relative adjustments about these best values.

The (V1,V2,V3) coordinates of the RAS source plate are set to the best values from the Dec 2000 or early Jan 2001 campaigns. The illumination of the fiber spots is then adjusted and balanced and test exposures taken to verify the aperture location of the fiber spots for refinement of the plate's (V2,V3) coordinates, if necessary. Ideally, for the WFC, the central fiber A1 should fall near pixel coordinates (2076,2152) to center all the fiber spots on the WFC sub-arrays read-out by the SMSs. The focus and tip-tilt SMSs are then executed and the focus and corrector mechanism positions refined. The HRC focus sweep is usually repeated at 5 points in the field by translating the A10 fiber : at the field centre, labeled HC (ID 24609), and at the four chip corners, labeled H2 (ID 24625), H3 (ID 24645) H6 (ID 24660), and H7 (ID 24680).

The RAS plate coordinates and best focus/cylinder positions from the Dec 2000 and early Jan 2001 alignment campaigns are listed in the following tables. Only the WFC point sources were aligned and focused in the early Jan 2001 campaign. The focus/cylinder positions for the WFC are global values for all nine fiber spots but for the HRC, only for fiber A10 at the field centre.

HRC (Dec 2000) 0.3862 0.2416 0.4487 A10 at (531,511)
WFC (Dec 2000) 0.3862 0.2487 0.4254 A1 at (2069,2131)
WFC (Jan 2001) 0.3862 0.2495 0.4201 A1 at (2076,2158)

HRC (Dec 2000) 56880 10366 2186
WFC (Dec 2000) 59652 40018 1959
WFC (Jan 2001) 59495 39838 2047


The various focus and tip-tilt SMSs are listed below and the complete description of each procedure is described in the SMS Master Table. Note : There are two versions of JRHW01A. In the first version (JRHW01A_A), originally used at BATC in June 2000, WFC1 is read-out with amp B and non-MPP timing patterns while in the second version, used in Dec 2000, it is read-out with Amp A and MPP timing patterns. The change was made because of a suspected problem with the bias of image sections read-out with Amp B in Dec 2000 (see the Dec 7, 2000 log), which was later fixed. Note that all these SMSs use a gain of 1 e-/DN and an offset of 0 for both detectors.


See the procedure descriptions in the SMS Master Table.


From the SMS Master Table, a single execution of all five procedures is ~7.5 hours. If the focus sweeps are repeated at the final, optimized focii, and at multiple locations in the HRC field, then the total time is ~11 hours. Overhead for focus and coma corrections, adjustment of the micrometers and the fiber light intensities, and other possible contingencies could easily increase the total time to ~15 hours.


See the procedure descriptions in the SMS Master Table.


A detailed step-by-step procedure was written by G. Hartig prior to this campaign. It also includes measurements of the residual abberation using phase retrieval.