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The NICMOS cameras were designed to share a common focus whose position can be adjusted using the Pupil Alignment Mechanism, or PAM. Unfortunately, the deformation of the NICMOS dewar caused large mechanical distortions within NICMOS, resulting in loss of a common focus for the three cameras. The difference between the NIC1 and NIC2 foci, is sufficiently small that an intermediate focus yields good quality images in both cameras; the NIC3, however, was pushed out of the range within which the PAM can adjust the focus position.

The focus for all 3 cameras changed significantly over the duration of Cycles 7 and 7N. Throughout Cycles 7 and 7N, the ongoing deformation processes in NICMOS kept changing the location of the detectors with respect to the PAM zero position. In addition, there were two periods of 2-3 weeks (the NIC3 Campaigns) during which the HST secondary mirror was adjusted to bring the focus back into the NIC3 PAM range.

Since the installation of the NCS, the focus has shown to be similar to that observed in Cycles 7 and 7N. The NIC1 and NIC2 focii have moved slightly in the negative direction, and the NIC3 focus has moved slightly in the positive direction, bringing it closer to focus. Furthermore, the focus has remained stable well-within acceptable limits. See the Post-NCS Focus Update as of 7/2/04 for more details on the most recent focus information.

The most relevant and important information on focus can be found in the following documents, which detail focus measurement techniques: Focus Measurements, and Instrument Science Reports (ISR-98-004), NICMOS Focus Monitoring and(ISR2007-003), NICMOS Focus Update.To learn more about the focus and breathing history of the entire telescope,visit the HST Observatory Focus Monitoring Website. The HST focus is described in micronsof secondary mirror movement, whereas the NICMOS focus is described in mm of PAMspace. The conversion factors are:

+1 mm of PAM =

For more specific details on the NICMOS focus, follow the links to the documents listed below.

NICMOS Focus Documentation

Important updates, discoveries and developments that could potentially affect NICMOS observations, calibration, or data analysis.

Frequently Asked Questions.

Performance Summaries:
Status reports reflecting the current understanding of instrument characteristics, performance and calibration.

Post-NCS NICMOS Focus Update: 7/2/04

Post-NCS NICMOS Focus History Table

Post-NCS NICMOS Focus Plot

NICMOS End Of Cryogen

Focus History from 1997-1999

NICMOS Focus History Table as of Jan 4, 1999

NICMOS Focus Monitoring Programs

Focus Measurements

NICMOS Focus: Design vs. On-Orbit Performance

NICMOS Cycle 7 PAM Setting and Focus

NICMOS Focus Update as of October 28, 1998

NICMOS Focus Update as of September 4, 1998

NICMOS Focus Update as of August 6, 1998

NICMOS Focus During the Second NIC3 Campaign

NICMOS Focus Update as of February 18, 1998

NICMOS Focus After January '98 NIC3 Campaign

NICMOS Focus During January '98 NIC3 Campaign

Images Near Best Focus

The NICMOS Instrument Handbook is the primary guide regarding the characteristics and use of the instrument. The HST Data Handbook is the primary guide for calibration, reduction and analysis of NICMOS data.

Instrument Science Reports:
ISRs are technical reports written by members of the NICMOS Group about various aspects of the instrument and data. They usually contain in-depth information about specific topics.

NICMOS ISR 2007-003: NICMOS Focus Update
H. McLaughlin 29 Jun 2007

NICMOS ISR 2003-005: NICMOS Focus Monitoring in the Year Following SMOV 3b
E. Roye 23 Apr 2003

NICMOS ISR 2002-002b: SM3B NICMOS Focus Check
A. B. Schultz 12 Jun 2002

NICMOS ISR-99-011: Long-Term Trends in the NICMOS Camera 2 Obscuration Pattern and Aberrations
J. Krist 15 Nov 1999

NICMOS ISR-99-003: NICMOS Optical Aberrations: Coma and Astigmatism
A. Suchkov 10 Jun 1999

NICMOS ISR-98-018: TinyTim modeling of NICMOS PSF subtraction: Effects of Focus Breathing, Cold Mask Wiggling, and Color Variations
A. Suchkov 11 Nov 1998

NICMOS ISR-98-016: NICMOS Focus Data Reduction and Analysis Using Phase Retrieval
G. Galas 15 Sep 1998

NICMOS ISR-98-015: NICMOS Focus and HST Breathing
A. Suchkov 15 Sep 1998

NICMOS ISR-98-013: Second NIC3 Campaign Results
A. D. Storrs 13 Jul 1998

NICMOS ISR-98-009: Focus Variation and the Orbital Phase of Observations
A. Storrs 14 May 1998

NICMOS ISR-98-007: Possible Evidence for NICMOS Focus 'Precessional Breathing'
A. Suchkov 01 May 1998

NICMOS ISR-98-005: NICMOS Focus Field Variations (FFV) and Focus Centering
A. Suchkov 16 Mar 1998

NICMOS ISR-98-004: NICMOS Focus Monitoring
A.Suchkov 16 Mar 1998

NICMOS ISR-1997-027: Camera 3 Performance
A. Storrs 01 Oct 1997

Papers and Proceedings:
Selected NICMOS related published papers and workshop proceedings.

Presentation from 2002 SPIE Meeting: Post-NCS Performance of the HST NICMOS
A. B. Schultz

NICMOS Flyer for June 2002 AAS Meeting

Long Term and Short Term Variations of NICMOS Foci
L. Bergeron,G. Galas

Cookbook style instructions, prescribed procedures, and helpful tips.

Examples of how to use various NICMOS-related tools, calibration and analysis techniques.

Space Telescope Analysis Newsletters:
STANs contain useful information regarding calibration and data reduction.

NICMOS STScI Analysis Newsletter 30
Discusses the NICMOS recovery from Safe Mode, the Mini-Check Out after recovery, Coronagraphic Observations, the Temperature Table, the Polarimetry Calibration, the Focus Monitor, post-SAA Darks, and recent NICMOS publications.
NICMOS Group 03 Oct 2003 (html)

NICMOS STScI Analysis Newsletter 3
Update on NICMOS Cycle 7 science program
and Exposure Time Calculator
NICMOS Group 01 Jun 1997 (html)

NICMOS STScI Analysis Newsletter 2
Focus update
Advice on the use of ORIENT, PATTERN-ORIENT, and POS TARG for Cycle 7
The Mr. Staypuft anomaly
The 'non-zero zeroth read problem'
NICMOS Group 31 May 1997 (html)