RFBG Commissioning: December 21-24, 2010 UT

Performance Verification Plan

General Description

There are three outstanding issues with operation of the RFBG focal station. Once these issue have been improved, understood and/or solved, then performance verification data can be collected.

The three issues (in order of priority) are:
  • "Mediocre" collimation and pointing models
  • "Poor" AGw stage transformation for probe motion
  • Collimation problems at low elevation
These three issues and the data collection will be discussed in the Issues section below.

The collection of performance verification data will be the same as the data collect in April for LDG focal stations, with a few improvements.

Tasks (in order to be performed)

Collimation and Pointing Model

ALERT! Collimation Model

A new collimation model MUST be determined before a new pointing model. See Collimation Model for instructions.

Seeing should be reasonable (<1.0")

ALERT!Pointing Model

See Pointing Model for instructions.

Can be marginal seeing (~1.0"-1.3")

ALERT!AGw Transformation Data Collection

See AGw Transform for instructions.

Need to update StoneO is on the Meridian at 21:47, StoneM at 17:51 and StoneL at 16:00 Sidereal.

ALERT!Collimation problems Data Collection

The collimation problems at low elevations are thought to be caused by the lenslet array of the wfsc not glued so the lenslet boundaries are parallel to the CCD pixel rows and columns. A new algorithm to determine the centroids of the wfsc image for a rotated lenslet was successfully installed and tests for the MODS wfsc at LDG. This same testing needs to be performed at RFBG.

The lenslet rotation for RFBG was found to be -0.7 degrees.

  • Confirm the collimation is slow and/or poor at low elevation before the lenslet rotation is added
    • preset to a BS star at about 30+-5 elevation in active mode
    • let GCS collimate for 10 minutes

  • Confirm the collimation is improved at low elevation with a lenslet rotation included
    • set WFS_lenslet_rotation to -0.7 in /lbt/tcs/current/etc/GCS/AIP_IRTC_R.cfg
    • preset to a BS star at about 30+-5 elevation in active mode
    • let GCS collimate for 10 minutes

Compare the convergence of these two cases.

Performance Verification

There are three types of data set that need to be collected, which are described later, to verify performance at the Left Direct Gregorian focal station:

  1. Presets
  2. Guiding and Collimation
  3. Offsets (5-Dice)

Several of each of these sets will be needed to get a complete picture of the performance of the focal station. Several type of information can be gleaned from each data set type.

Description of Data Set Types


A presets data set consists of multiple presets to the same target and off-axis guide star with the same position angle (PA). The purpose is to check the repeatability of the all the systems needed to preset, in ACTIVE mode, at different elevations and at different times.

Data Set Requirements

It would be best to have four sets of Preset Data sets.

  • 6 to 8 presets in the elevation range from 30 to 85 degrees
  • Same off-axis (off the Y-axis would be best) guide star
  • Same position angle (say PA=0 for a correctly orientated guide star)
  • Offset telescope by 30"
  • Collect background IRTC images with same parameters as above
  • Allow active optics corrections (Note, one correction can be performed during background collection)
  • Collect IRTC for 30 seconds total integration time (cubes 15 images with 2 second integrations)

Each set, with 6 to 8 points, could be all increasing or decreasing in elevation, or could be both increasing and decreasing elevation (ie collect data on a star from 30, through zenith, and back down to 30)

*Note:* Some data points could be drawn from the Guiding and Collimation Data Sets (See below)

ALERT!Guiding and Collimation

A guiding and collimation data set consists of presetting the telescope to a target, that can be seen on IRTC and using an off-axis guide star, and allowing the telescope to follow the star for at least 15 minutes. These data sets will contain information about:

  • How well is Guiding working
  • How well Active Optics is working
  • Image quality from IRTC (FWHM to compare to guider value, ellipticity)

Data Set Requirements

We should collect 6 to 8 sets with a range of conditions:

  1. Elevation from 30 to 85 degrees
  2. Range of off-axis guide probe positions
  3. Two sets at the same elevation with all parameters the same expect PA=0 and PA=INDEF
  4. Various guide star magnitudes (10th to 16th magnitude...should be to 18th mag)

The steps to acquire these data are

  • pointto "Star" TelMode=Active gs=# PA=0 (or 90, or 180, or -90)
  • Acquire background - offset 0 30 - Acquire 30 sec IRTC cube - offset 0 0
  • Acquire 30 sec IRTC Cubes continuously for 15 to 20 minutes

ALERT!Offsets (dice5)

A Dice5 data set consists of presetting the telescope to a target that can be seen on IRTC and then offsetting a given amount in a pattern of the five spots on a di. These data will allow us to understand the accuracy and repeatability of the offsets. Plus these data can be used to analyze image quality.

Data Set Requirements

Dice5 data sets should include the following parameters:

  • Offsets should span a range of distances, say 1", 10" and 3'
  • They should span elevations from 30 to 85

The steps to acquire these data are

  • pointto "Star" TelMode=Active gs=# PA=0 (or 90, or 180, or -90)
  • Acquire background - offset 0 30 - Acquire 60 sec IRTC cube - offset 0 0
  • Start dice5 IRAF routine with appropriate offset amount and 2 sec. exposures and 30 image

ALERT!Field Data

Collect a set of field data with 12 stars to confirm the amount of aberration due the mis-alignment of the primary and secondary

Data Collection

See description of the IDL collection routine in Field Aberration Measurements

Data Analysis

See description of the IDL processing routine in Field Aberration Measurements

Data Set Requirements

-- DougMiller - 19 Dec 2010
Topic revision: r4 - 23 Dec 2010, DougMiller
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