6  The Multiple Instrument System (MIS)

When initializing or starting an observing run make sure that RETROCAM mirror/prism is Out

by double clicking on the Out button in the MIS. RETROCAM icon should say Moving if the mirror/prism

is not truly Out.

 

6.1) Introduction

6.2) The MIS Cameras

6.3) The Multiple Instrument System Control Software, xmis

6.4) Now called RETROCAM (Finder Camera no longer exists)

6.4.1) Wide field acquisition of astronomical objects can be done with RETROCAM

6.4.2) Spectroscopic calibration

6.5) Guider

6.5.1) xmis guider parameters

6.5.1) Off-axis guiding for direct imaging

6.5.2) Slit plate guiding for spectroscopy

6.6) How to Focus Guider and the Instrument

6.6.1) Focus procedure: direct imaging

6.6.2) Focus procedure: spectroscopy

6.6.3) Coarse focus of the guider.

6.7) MIS Filter wheel

6.7.1) Introduction

6.7.2) How to change filters

6.7.3) The MDM Johnson UBVRI filter sets

6.8) Technical Reference Section

6.8.1) Guest instrumentation and the MIS mounting plate

6.8.2) MIS Controller: FORTH commands (for staff use only)

6.8.3) xmis software configuration (for staff use only)

6.1  INTRODUCTION

The Multiple Instrument System (MIS) comprises three discrete and independent modules which can be used with a suite of analytical instruments: finder, guider and filterwheel (Figure 6.1).

The finder(see RETROCAM Manual) and guider modules are equipped with a video camera for object acquisition (with RETOCAM) and guidance. In addition, the finder module contains spectral calibration and flat field lamps.

The filter wheel module, which also contains a shutter, is used with imaging detectors and some spectrographs when employed as image reduction cameras.

The MIS modules are attached to the instrument rotator (Chapter 8) and changing the rotator angle will alter the orientation of the finder and guider fields.

The operation of the MIS is linked with several other units which must be turned on for acquisition and guidance (Figure 6.2). Only those items located in the observing room are normally powered down at the end of the night. Note the MIS hatch, which must be open to admit starlight!

The MIS modules communicate through the MIS control crate which is located in the right center instrument rack of the computer room. There are only two controls on the front panel of this rack: a power switch and a reset button. Fuses are located on the back panel.

Figure 6-1: Finder-Guider-Filter Wheel Optics


Figure 6-2: MIS Control Schematic


Figure 6-3: Guider System Checkout


6.2     The MIS Camera(guider)

 No finder camera(see RETROCAM Manual) the guider is equipped with a low-light-level video camera which gives a real time display on the GUIDE MONITOR.

The camera head is a Fairchild 3000F CCD with 378 x 488 pixels, a 14 mm image diagonal and a 4:3 aspect ratio. The CCD has a low light level dynamic range of 1000:1 and a minimum useful illumination of 5 lux. The spectral response peaks in the red at 8000A. The camera is equipped with a coherent fiber optic faceplate which allows it to be coupled (using a drop of immersion oil) to a four-stage Varo electrostatic image intensifier.

Each camera head has an independent power supply, mounted on the instrument rotator flange. These units are normally left ON, with the SYNC switch set to INTERNAL; they must be powered down when the camera cables are disconnected to avoid damage to the CCD.

For an image to appear on the GUIDE MONITOR three units must be powered up:

Power to the image intensifier is controlled by the guide CAMERA SELECTOR. The Digital Video Integrator, if used, should be set to DIRECT to see starlight unless you have already set the digital levels. The Digital Video Integrator is only capable of processing signals from one camera and so the CAMERA SELECTOR is used to switch to the desired camera and only apply voltage to that image intensifier. The applied voltage must be in the range 0 to 6.75 volts and the normal operating range is 4 to 6 volts. The response is very non-linear and very rapid, so turn the gain up slowly (taking 3 to 5 seconds) while watching the GUIDE MONITOR. A crowbar circuit trips the power if more than 6.4 volts is applied. Turn the gain all the way down to reset the crowbar. Also turn the gain down when switching between cameras or when slewing the telescope to a new field.

After power has been applied to the image tube it may take 30 seconds (or many minutes, depending on the humidity) for the charge to bleed away; be careful when moving to brighter standard stars.

The guider camera can be rotated in the MIS to align them along the compass points. Contact the staff if you believe there is an alignment problem. Note that the display orientation changes with position angle of the instrument rotator (Chapter 8), and for direct versus slit plate guiding (Section 7.5).

If you experience difficulty in acquiring objects in the guider consult Figure 6.3 for a system checkout.

Figure 6-4: Main xmis Window

6.3  The Multiple Instrument System Control Software, xmis

The MIS control crate is connected to the observer's console (hiltner) and commands to operate the various slides, lamps and filter wheels are entered through the xmis window (Figure 6.4) using a mouse and keyboard. When the filter wheel is not used the information on the filters is not displayed in the window.

Start-up procedures for the software are described in section 4.3.4; this chapter assumes you are familiar with all of Chapter 4.

When the software is loaded a large red box with the word INITIALIZE appears. Click on this with the mouse to initialize communications with the MIS control crate. Use the xmis SETUP menu to initialize or quit the software at any time. If one or more of the modules fails to initialize using xmis, but continues after pressing the reset button on the control crate, check the fuses at the back of the control crate.

6.4  RETROCAM

The RETROCAM serve some basic functions:

6.4.1  Wide field acquisition of astronomical objects.

The position of the main sliding RETROCAM prism determines which function is accessible. When the RETROCAM prism is IN the starlight to the your instrument is blocked; however there is a ~100 arcminx2  horseshape guide field for the guide probe, star light is reflected to the wide field RETROCAM CCD

To acquire an astronomical object with the RETROCAM:

  1. Open the dome and then the telescope mirror covers.
  2. Open the MIS HATCH (located above the finder to the E. for zero rotation).
  3. Put the RETROCAM to In:

o        click the mouse on the xmis RETROCAM In box

o        it takes 20 seconds to move fully in.

4.      Select a suitable RETROCAM FILTER.

.

6.4.2  Spectroscopic calibration.

Spectroscopic calibration is also done with the RETROCAM IN. Light from emission lamps or flat field lamp is reflected off the underneath of the RETROCAM prism. To obtain calibration arcs or flat fields:

1.      Darken the environment to prevent ``light leaks''.

o        Close the louvres in the dome during the day.

o        Leave the MIS HATCH closed.

2.      Put the RETROCAM to In

o        Click the mouse on the xmis RETOCAM In box

o        It takes 20 seconds to move fully in

3.      that the guider probe is not at Slit [Guider: S(10600, 0)]

4.      Turn on the required MIS lamp by clicking the mouse once on the lamps box. Then select the required lamp in the pop-up window. Any lamps which are on will be highlighted.

5.      Take an exposure (try 0.5 seconds for Ne, 20 seconds for Xe).

6.      Remember to turn the lamp off when you have done! You can have more than one of the MIS Lamps illuminated at once. To turn them all off click on the Off box. To turn individual lamps off click on that lamp. If you close down the Lamps pop-up window with the lamps on the Lamps box will turn red.

Neon, argon, mercury-neon and xenon spectral lamps and an incandescent (quartz) continuum source are all available. A spectral atlas for each lamp, together with typical grism settings, is provided in the manual for each spectrograph.

6.5  GUIDER

The RETROCAM mirror must be OUT to allow starlight to reach your instrument. But can be used with RETROCAM (see RETROCAM User Guide)

The guider can be used in one of two modes:

An autoguider is available and is described in Section 7.3, which assumes that you are familiar with the contents of this section.

The guider has a diagonal probe whose minor axis is 25.4 mm. The probe can move in x and y directions as specified in Figure 6.5.

The probe has four basic positions accessible through the Preset pop-up menu:

6.5.1  xmis guider parameters; Preset pop-up menu

The probe can be moved to the first three positions selecting the destination in the xmis Preset pop-up window. The coordinates of the guider probe, together with the message [O], [C] or [S] are displayed in the xmis window:

· Origin:

Guider: O

(0,

0)

· Center:

Guider: C

(11040,

10050)

· Slit:

Guider: S

(10600,

0)

Units: probe

The default coordinates, given in motor steps where 1 step moves the probe 6.8 mm, or 0.078 arcseconds at f/7.5 and 0.043 arcseconds at f/13.5

Units: mm

The scale is set to 0.00680 to display the probe coordinates in millimeters.

Units: arcsec

The scale is set to 0.07839 to display the probe coordinates in arcseconds at f/7.5.

Units: user (Scale)

Allows the scale to be changed for other focal ratios. The motor moves the probe 6.8 mm per step. Entering 0.04351 displays the probe coordinates in arcseconds for the f/13.5 focus.

Zero coords

The zero point of the probe can be set to the optical axis or other point if you want to do special offsets.

6.5.2  Off-axis guiding for direct imaging.

The probe can move off-axis in x and y directions as specified in Figure 6.5. The SLIT VIEWING OPTICS vignette just a fraction of the available field. Pull the plunger out if this interferes with your upward looking optics guide stars.

Figure 6-5: GUIDER PROBE X-Y COORDINATE MAP


There are two ways to move to an off-axis position ``?'', using either absolute or incremental instructions.

X pos: Y pos:

To move the probe in absolute coordinates, place the mouse in the X pos box, type in the desired value and press enter. You will see the message ``probe moving'' and then the new position will be displayed. Repeat the procedure for the desired Y pos.

dX: dY:

To move the probe by an incremental amount place the mouse in the dX: box and enter the desired amount of movement. Repeat for dY:. 1000 counts will move a star about halfway across the field. Positive numbers move the star right (dX:) and up (dY:) (assuming rotator angle of zero) and negative numbers go the opposite way.

Stop

If you are scanning for a guide star and you see a suitable object moving across the field click on the Stop box to arrest the motion.

6.5.3  Slit plate guiding for spectroscopy.

The RETROCAM prism must be OUT to allow starlight to reach the guider and your spectrograph.

Use the xmis Preset menu to move the guider probe to Slit. Check that the SLIT VIEWING OPTICS are IN. Put the CAMERA SELECTOR to GUIDER. You should now see the star reflected off the slit. If you do not then consult Figure 6.3 for a system check-out.

If the slit and the finder are not collimated to each other then try a minor ``tweak'' on the slit viewer plunger. Use the TV monitor in the dome to check interactively.

If there is no suitable guide star on the slit plate you can swap to off-axis guiding once you have centered the object on the slit. See section 6.5.2 for this. You will have to re-focus the guider using the guider focus hand paddle (located to the left of the guide monitor) and you must also change the autoguider orientation parameters (section 7.5). To get back to viewing the slit use the xmis preset Slit command and refocus the guider again.

6.6  HOW TO FOCUS THE GUIDER AND YOUR INSTRUMENT

This section assumes you are familiar with the preceding sections. The procedure is different for direct imaging and spectroscopy. Once everything is aligned and focussed you can note the field centers using the DVI hand paddle (Section 7.4)

6.6.1  Focus procedure: direct imaging.

  1. Acquire a bright (about mV = 8) star in the finder (Section 6.4.1)
  2. Bring your instrument (telescope) in to focus:

o        Put  RETROCAM to Out

o        Put the CAMERA SELECTOR to GUIDER.

o        Move the guider probe to Center through the Preset pop-up menu.

o        Center the star on the GUIDE TV then move the guider away from center.

o        Center the star on the detector.

o        Focus the telescope by moving the secondary mirror:

§         use the telescope hand paddle

§         IN drives the focal plane UP

§         OUT drives the focal plane DOWN

§         SET + IN or SET + OUT gives a rapid focus change

§         1 focus unit = 0.07 mm at f/7.5 or 0.2 mm at f/13.5

  1. Bring the guider in to focus:

o        The guider does not have neutral density filters - keep the voltage down or move to a fainter star.

o        Put the CAMERA SELECTOR to GUIDER.

o        Move the guider probe to Center through the Preset pop-up menu.

o        Focus using the guider focus hand paddle (to the left of the find/guide monitor).

o        Keep the DVI integration time below 0.5 second where possible.

o        If you cannot achieve focus refer to section 6.6.3

       

6.6.2  Focus procedure: spectroscopy.

1.      Acquire a bright (about mV = 8) star in the  RETROCAM (Section 6.4.1)

2.      Bring the guider (slit plate) in to focus:

o        This can be done during the day.

o        Leave  RETROCAM  In.

o        Put the guider probe to Slit, if using Modspec or MKIII .

o        Check that the SLIT VIEWING OPTICS are IN  if using Modspec or MKIII  not the CCDS (normally true).

o        Put the CAMERA SELECTOR to GUIDER.

o        Turn on the Flat arc lamp.

o        Set the CAMERA SELECTOR voltage gain to about 1 volt.

o        Focus using the guider focus hand paddle (to the left of the guide monitor).

o        Keep the DVI integration time (if using) below 0.5 second where possible.

o        When in focus some scratches may be visible on the slit plate.

o        If you cannot achieve focus refer to section 6.6.3

3.      Turn off the Flat lamp and put  RETROCAM to Out.

4.      Focus the telescope on the slit plate:

o        The guider does not have neutral density filters - keep the voltage down or move to a fainter star.

o        Keep the DVI integration (if used) time below 0.5 second where possible.

o        Focus the telescope by moving the secondary mirror:

§         use the telescope hand paddle

§         IN drives the focal plane UP

§         OUT drives the focal plane DOWN

§         SET + IN or SET + OUT gives a rapid focus change

§         1 focus unit = 0.07 mm at f/7.5 or 0.2 mm at f/13.5

  1. Focus the spectrograph:

o        Normally done by the staff for your requested grism settings.

o        Follow the instructions in the spectrograph manual when necessary.

6.6.3  Coarse Focus of the Guider

The guider box has a coarse focus which allows instruments to sit at different back focal distances. If you cannot achieve focus with the guider box hand paddle (located to the right of the TELESCOPE MONITOR) then you will need to adjust the coarse focus. The electrical motor which provides guider fine focus adjustments is mounted on a moveable stage. Coarse focus is obtained by translating this stage by hand using the following procedure:

6.7  Filter Wheel

6.7.1  Introduction

The filter wheel houses a wheel which holds up to 8 filters. It can accommodate 2 inch square, 2 inch round, 1 inch round and other sizes by special adaptors. The standard MDM UBVRI filter set, when requested, will be loaded by the staff; see section 6.7.2 to load filters yourself.

The filter wheel is moved through the xmis window, the current filter being highlighted in yellow.

To have xmis display the names of custom-filters in the wheel: 

·                 
·                    misfilter
·                 
·                    xmis &

in an xterm window.

6.7.2  How to change filters

You can gain access to the change door while the box is mounted to the telescope, allowing more than 8 filters to be used if necessary. The filter positions are marked 0 through 7. When filter 0 is in the beam filter 4 is accessible through the filter door. A special, rather fragile, tool is used to install and remove the filters. Do not overtighten the screws. Thermal changes can cause the pressure to increase and the filters to crack!

As of September 1995 we can no longer borrow filters from NOAO.

6.7.3  The MDM Johnson UBVRI filter sets

Two new UBVRI filter sets, two inches square, were acquired in 1990 (the old ones were broken by overtightening the retaining clamps). If you request these filters they will be installed for you by the staff.

The prescription of the glass used for these sets, designed by Jim Schombert while he was at Michigan, is as follows:

FILTER

Glass

U

Schott UG-1, WG-280, Hoya CM-500

B

Schott BG-12, BG-39, GG-385

V

Schott GG-495, BG-18

R

Schott OG-570, KG-3

I

Schott RG-715

Unfortunately, they are of different thickness and not parfocal. The filters were cemented, polished better than 50 microns, and MgFl2 anti-reflection coated by Fish-Schurman in New York. Tracings of the filters (Figure 6.6) show that this set is similar to the Harris formula used on Kitt Peak, with some noticeable exceptions:

The U filter does not use a liquid CuSO4 cell, but rather a new red blocking glass called CM-500 from Hoya optical.

The B filter has been cut sharper at the red side than the original Johnson formula in order to more clearly separate the relative fluxes in the B and V bands. This produces slightly better color information in galaxies.

The R filter has a longer tail than the original Johnson R, a result of the lack of good glass beyond 6000Å. It has a red leak at l > 1.05 mm.

The I filter is an interference-type filter (Cousins I) instead of the old-style Johnson I that had its exact response determined by the red-cutoff of the CCD response.

Figure 6-6: Schombert Filter Set Transmission Curves


6.8  Technical Reference Section

6.8.1  Guest Instrumentation and the MIS mounting plate

The finder, guider and filterbox modules of the MIS all have the same basic 12 mounting holes (Figure 6.7). These holes, 0.625 DIA, take reducing bushings and nuts. These are available in stainless steel and nylon. An electrical isolating spacer, made of G10, is also available.

The vertical height of each box is shown in Figure 6.1; a variety of back focal distances can be accommodated by using a combination of the modules:

Modules used

remaining back focal distance (inches)

 

 

none

15.72

Finder

7.25

Finder + Guider

3.00

Finder + Guider + Filter wheel

0.50

If the MIS is not used at all, the instrumentation can be mounted directly on the instrument rotator (Section 8).

The diameter of the central hole in the FINDER and GUIDER boxes is 177.8 mm (7.0 inches), and the unvignetted field diameter of the telescope at f/7.5 is 125 mm (5 inches). The guider probe and the slit-viewing optics both vignette this field (Figure 6.5).

The slit viewing optics were designed for use with a focal plane 63.5 mm (2.50 inches) below the guider box. The optimal focal plane of the telescope, however, lies 76.2 mm (3.00 inches) below the guider. The slit viewing optics can be adjusted to accommodate slit planes from approximately 50 to 81 mm (2.0 to 3.2 inches) below the guider box. The FILTER WHEEL has, in addition to the 12 mounting holes around the perimeter which take the reducing bushings, 8 holes tapped 1/4- 20 as shown. The central hole is 2.25 inches in diameter.

The maximum total weight of the instrument depends upon its distance and distribution from the instrument rotator, and is approximately 500 pounds (225 kg). A moving platform allows heavy instruments to be raised for attachment to the telescope. Please consult the staff at an early stage if you plan on bringing out your own instrumentation.

Figure 6-7: MIS Mounting Plate Dimensions


6.8.2  MIS Controller: FORTH commands (for staff use only)

The MIS control crate microprocessor is programmed in FORTH. It communicates with the telescope control computer, hiltner, through an X-windows package, called xmis, developed by John Tonry and Mark Metzger of M.I.T.

It can also be controlled through a dumb terminal by issuing commands: SEE THE STAFF FOR A LIST OF COMMANDS, (NO USER FRIENDLY PARTS), IF THERE IS A PROBLEM USING THE XMIS WINDOW!!!!

6.8.3 xmis software configuration (for staff use only)

Staff notice for instrument changes: The xmis software needs to know which of the three MIS modules are installed. The telconfig script is used to setup both the TCS and MIS configuration for a given telescope and instrument combination. See the Startup Guide for details.

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Updated: 2006-12-01, RBarr (MDM)