NICMOS Focus

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 Monitering 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 microns of secondary mirror movement, whereas the NICMOS focus is described in mm of PAM space. The conversion factors are:

+1 mm of PAM =

• NIC 1 : -7.83 um of secondary motion
• NIC 2 : -7.92 um of secondary motion
• NIC 3 : -8.5 um of secondary motion

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

NICMOS Focus Documentation

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

FAQs:
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
This document presents the current status of the NICMOS focus and the most recent NICMOS focus monitering results.
E. Roye 16 Oct 2002 (html)

Post-NCS NICMOS Focus History Table
This table shows the focus history measurements made during the focus monitering programs for all three cameras after the installation of the NCS.
E. Roye 16 Jul 2002 (html)

Post-NCS NICMOS Focus Plot
Shows a plot of the focus history for all three cameras since the installation of the NCS.
E. Roye 06 Jul 2002 (gif)

NICMOS End Of Cryogen
In order to estimate NICMOS performance during the NCS era, a monitoring program was executed to follow the detector characteristics during the End ofCryogen warmup of the instrument. Flatfields, focus variations, and dark current was monitored.
NICMOS Group 01 Nov 2001 (html)

NICMOS Focus History Table as of Jan 4, 1999
A tabular display of the focus history for the three NICMOS cameras.
NICMOS Group 04 Jan 1999 (html)

Focus History from 1997-1999
A brief discussion and table describing the history of the NICMOS focus through January, 1999.
NICMOS Group 04 Jan 1999 (html)

NICMOS Focus Monitoring Programs
Due to varying mechanical stresses in the dewar, the focus of the NICMOS detectors was constantly changing on-orbit. A series of programs were designed to monitor the focus for each of the three cameras.
NICMOS Group 04 Jan 1999 (html)

Focus Measurements
A discussion of the three methods used to measure the NICMOS focus: encircled energy, phase retrieval, and plate scale.
NICMOS Group 04 Jan 1999 (html)

NICMOS Focus: Design vs. On-Orbit Performance
The NICMOS design is compared to its on-orbit performance with regard to focus.
NICMOS Group 04 Jan 1999 (html)

NICMOS Cycle 7 PAM Setting and Focus
Current PAM settings and actual focci for the three NICMOS cameras.
NICMOS Group 12 Nov 1998 (html)

NICMOS Focus Update as of October 28, 1998
Update on the NICMOS focus as of October 28, 1998.
NICMOS Group 28 Oct 1998 (html)

NICMOS Focus Update as of September 4, 1998
Update on the NICMOS focus as of September 4, 1998.
NICMOS Group 04 Sep 1998 (html)

NICMOS Focus Update as of August 6, 1998
An update of the state of the NICMOS focus as of August 6, 1998.
NICMOS Group 06 Aug 1998 (html)

NICMOS Focus During the Second NIC3 Campaign
A report of the NICMOS focus during the second NIC3 focusing campaign in June of 1998.
NICMOS Group 04 Jun 1998 (html)

NICMOS Focus Update as of February 18, 1998
An update of the NICMOS focus as of February 18, 1998.
NICMOS Group 18 Feb 1998 (html)

NICMOS Focus After January '98 NIC3 Campaign
Status of the NICMOS focus after the January, 1998 NIC3 campaign.
NICMOS Group 01 Feb 1998 (html)

NICMOS Focus During January '98 NIC3 Campaign
A report of the NICMOS focus during the January, 1998 NIC3 campaign.
NICMOS Group 19 Jan 1998 (html)

Images Near Best Focus
Images of NGC 3603 at the best focus in all three cameras.
NICMOS Group 18 Jun 1997 (html)

Handbooks:
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
This ISR will address a number of changes in the way the NICMOS focus is monitored. It will provide a detailed explanation of those changes and a step-by-step description of the new procedure. The ISR also highlights the results of the focus checks after the HST safing event, which caused the NICMOS cooling system (NCS) anomalous shutdown in February of 2007.
H. McLaughlin 29 Jun 2007 (pdf)

NICMOS ISR 2003-005: NICMOS Focus Monitoring in the Year Following SMOV 3b
Monthly monitoring of the NICMOS focus since SMOV 3b, following the installation of the NICMOS Cooling System (NCS) has revealed stable and consistent focus measurements in all three cameras. The focus values for each camera, which were measured and uplinked to the Telescope during SMOV 3b are accurate and have not required any revision.
E. Roye 23 Apr 2003 (pdf)

NICMOS ISR 2002-002b: SM3B NICMOS Focus Check
We report determinations of the NICMOS foci following cool down of the NICMOS detectors after installation and activation of the NICMOS Cooling System (NCS). A focus sweep in all three cameras executed on May 3, 2002 (program ID: 8977). Visual inspection of the data indicated that a small amount of coma had been introduced since January 1999. Phase retrieval (STScI) and encircled energy (University of Arizona) measurements were used to determine the best focus positions. The results of the two methods compared quite favorably with each other. Adjustments to the current Pupil Alignment Mechanism (PAM) positions were implemented on May 9, 2002 for Camera 1 & 2 (PAM1 & PAM2). No focus adjustments were implemented for Camera 3 (PAM3) or for the Camera 2 coronagraphic focus (PAMC). Adjustment of the intermediate focus position between Camera 1 & 2 (PAMI) will be managed starting during week 2002.133 by SMS.
A. B. Schultz 12 Jun 2002 (pdf)

NICMOS ISR-99-011: Long-Term Trends in the NICMOS Camera 2 Obscuration Pattern and Aberrations
Phase retrieval measurements of well-exposed NICMOS Camera 2 star images show that long-term changes occurred in coma and the cold mask position over the 1997-1998 lifespan of the instrument. The derived trends have been implemented in Version 5 of Tiny Tim.
J. Krist 15 Nov 1999 (pdf)

NICMOS ISR-99-003: NICMOS Optical Aberrations: Coma and Astigmatism
Trends in coma and astigmatism for each of the three NICMOS cameras have been derived using phase retrieval analysis of the data from the NICMOS focus monitoring program.
A. Suchkov 10 Jun 1999 (pdf)

NICMOS ISR-98-018: TinyTim modeling of NICMOS PSF subtraction: Effects of Focus Breathing, Cold Mask Wiggling, and Color Variations
We conduct TinyTim modeling of NICMOS camera 2 PSFs to assess limits to the accuracy of PSF subtraction imposed by color dependence, OTA focus breathing, and cold mask wiggling.
A. Suchkov 11 Nov 1998 (pdf)

NICMOS ISR-98-016: NICMOS Focus Data Reduction and Analysis Using Phase Retrieval
This ISR documents the process of measuring NICMOS focus and is written as a tutorial that can be used by anyone wishing to learn focus data reduction and analysis using the phase retrieval technique.
G. Galas 15 Sep 1998 (pdf)

NICMOS ISR-98-015: NICMOS Focus and HST Breathing
Biweekly NICMOS focus monitoring measurements are compared with the predictions of the three OTA focus breathing models.
A. Suchkov 15 Sep 1998 (pdf)

NICMOS ISR-98-013: Second NIC3 Campaign Results
This report describes the point spread function (PSF) information for data taken in the second NICMOS camera 3 (NIC3) refocus campaign.
A. D. Storrs 13 Jul 1998 (pdf)

NICMOS ISR-98-009: Focus Variation and the Orbital Phase of Observations
We report the effects of cyclic OTA 'breathing' on focus position for a variety of observational strategies with special attention given to NICMOS coronagraphic observations of bright targets.
A. Storrs 14 May 1998 (pdf)

NICMOS ISR-98-007: Possible Evidence for NICMOS Focus 'Precessional Breathing'
Combining the results of measurements of NICMOS focus and temperature (outside NICMOS dewar), we have found a correlation between detrended NICMOS focus and detrended temperature. The correlation suggests that there is a thermally induced (quasi)periodic component in NICMOS focus variation which has a time scale resembling the HST precessional period.
A. Suchkov 01 May 1998 (pdf)

NICMOS ISR-98-005: NICMOS Focus Field Variations (FFV) and Focus Centering
We present empirical results of a study of time dependence as well as PAM setting dependence of the variation of focus across the detectors' field of view for the NICMOS cameras.
A. Suchkov 16 Mar 1998 (pdf)

NICMOS ISR-98-004: NICMOS Focus Monitoring
We describe techniques to measure NICMOS foci and present the results of the NICMOS focus monitoring program as of February 1998. Procedures to correct for various affects which impact focus measurements are discussed.
A.Suchkov 16 Mar 1998 (pdf)

NICMOS ISR-027: Camera 3 Performance
We present information on the curent optical performance of NICMOS camera 3 (NIC3) at J, H, and K, obtained without moving the HST secondary mirror, i.e. the performance obtainable today, outside a NIC3 'campaign'. We also assess the performance that can be expected if the HST secondary is refocused to bring NIC3 into focus.
A. Storrs 01 Oct 1997 (pdf)

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

Tutorials:
Cookbook style instructions, prescribed procedures, and helpful tips.

Examples:
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)