RFBG Commissioning: March 24-25, 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" pointing model
  • "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 of priority unless poor seeing)

ALERT!AGw Transformation Data Collection

See AGw Transform for instructions.

Seeing should be better than 0.9"

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

Collimation problems Data Collection

Seeing should be better than 0.9"

ALERT!Lenslet Rotation Test

One possible cause of collimation problems at low elevations may be that the lenslet array of the wfsc was 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 tested 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.

ALERT!Differential Refraction

Another possible cause of collimation problems at low elevations may be the differential atmospheric refraction between the guider wavelength and the wfsc wavelength displaces the wfsc pupil enough at low elevation to get some vignetting on the pinhole in front of the wfsc.

To test this hypothesis we will change the guider x,y hotspot and see if the vignetting of the wfsc image changes.

  • Preset to a high (>75) elevation star with a bright (<12) guidestar
    • Set wfsc integration time to 10 seconds
    • Collect two wfcs images
    • Change guide_x_hotspot by 10 pixels (0.5 arcseconds) in AIP_IRTC_R.cfg
    • Send new preset if needed (Torsten?)
    • Collect two wfsc images
    • Change guide_x_hotspot by -10 pixels (-0.5 arcseconds) in AIP_IRTC_R.cfg
    • Send new preset if needed
    • Collect two wfsc images
    • Change guide_y_hotspot by 10 pixels (0.5 arcseconds) in AIP_IRTC_R.cfg
    • Send new preset if needed (Torsten?)
    • Collect two wfsc images
    • Change guide_y_hotspot by -10 pixels (-0.5 arcseconds) in AIP_IRTC_R.cfg
    • Send new preset if needed
    • Collect two wfsc images

  • Preset to a low (~30) elevation star with a bright (<12) guidestar
    • Perform same sequence as above

ALERT!Pointing Model

See Pointing Model for instructions.

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

Performance Verification

In the past we have used a table (see below) to keep track of performance verification data. As data sets are collected for each type of data and at each elevation the directory name where the data are held is placed in the appropriate column. I have placed a few examples in this table.

Elevation Preset Guiding/Collimation Dice5 (1x1) Dice5 (10x10) Large Offsets (1'-3')
30     dice1_30a dice1_30b    
45   col_45a col_45b      
60       dice10_60a  
75         dice_big_75a

Description of Data Set Types

Presets

A presets data set consists of multiple presets at various elevations 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 75 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)

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 75 degrees
  2. Range of off-axis guide probe positions
  3. Two sets at the same elevation with all parameters the same expect PA=60 and PA=-60
  4. Various guide star magnitudes (10th to 16th magnitude...should be to 18th mag)

Data Set Acquisition

See Guiding and Collimating for instructions.

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 75
  • Persson (BS) or Stone fields are best to use

Data Set Acquisition

See Dice5 for instructions.

-- DougMiller - 11 Mar 2011
Topic revision: r1 - 11 Mar 2011, DougMiller
This site is powered by FoswikiCopyright © by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding Foswiki? Send feedback