Binocular Observing with Mixed Instrument Pairs at LBT


This wiki page is intended to collect the present and possibly arcane knowledge about binocular observations at LBT with mixed instrument pairs.


For an overview of Binocular Observing with TCS, see Binocular Observing 101 (481s625f) and references therein. It is important to read that document to follow the binocular lingo on this page. The TCS supports fully binocular observing with matched or mixed instruments, however not all of the instrument interfaces are ready for such observing. Thus, there are a few tricks to make it all play together.


In binocular mode, both sides must send an eventually successful preset for everything (tracking, guiding and collimation) to work. The preset state cannot be "None" or "Cancelled" on either side for your OB to be successful.

Co-Pointing Limit

The default co-pointing limit is 40 arcsec radius on either side in April 2014. This limit is applied in equatorial (RA/DEC) coordinates. Speak to John Hill if you need larger offsets of the two targets (can be up to 120 arcsec in particular directions.) A voice alarm will inform you if any copointing or mirror travel limits have been violated.

WARNING near zenith

The default 40 arcsec co-pointing limit is deliberately set to be a number which is "good all the time". An exception may be close to zenith where the two primary mirrors become more wall-eyed due to gravity deflection. That deflection makes the practical co-pointing become asymmetrical left-right, so you could pass the copointing limit check and still have problems with limits of primary mirror tip-tilt.


The LBTplot GUI now has a "cpoint" plot which displays the instantaneous available co-pointing (apparent mis-pointing) range for the two sides of LBT. The blue diamonds show the present (for the plot) optics tip-tilt, and the circles show the available range of tip-tilt (Mode 1 pointing moving M1 and M2 together) limited by various optics motions. The tiny black dots show the history of the co-pointing over the time span of the plot.

Co-Pointing Errors

If you send a asynchronous preset or a large RADEC offset which exceeds the co-pointing limit, the TCS will audibly complain, and will not execute the preset/offset. (Since Build 2015A, PCS has a button to disable the co-pointing limit check. See the "Pointing Details" subGUI of PCS.) One must be careful that, with the asynchronous (i.e. LUCI1 and LBCR) dithers, each of the two sides will never be commanded to point to locations which exceed the "co-pointing radius". With slightly less restriction, one must be careful that, with synchronous dithers, the two sides will never be commanded to point to locations separated by more than the twice the "co-pointing radius".

Changes to the pointing model (IE/CA) are not protected in that same way, so sending large pointing corrections can run the optics into their software limits of travel. These pointing corrections are only an issue above EL=80 where not all of the pointing models are well matched. ( ptautoadjust is the IRAF script for centering one side of LBC. )

Similarly large DETXY offsets are not protected, so large DETXY offsets can also run the optics into their software limits of travel.

(need descriptions of the co-pointing errors and warnings here)

Mixed Instrument Combinations in Binocular Mode

Synchronous Presets

LUCI1 and one-sided LBC are hardwired to send the BinocularControl SYNCPRESET flag in front of all presets, but MODS1 is not. (That hardwired configuration for LUCI1 will be removed when we convert to using the binocular-capable LUCI2 software on both sides of LUCI in 2015.)

Synchronous Offsets

LUCI1 does not send the BinocularControl SYNCOFFSET flag in front of offsets (in order to allow small dither motions along the slit without disturbing observations on the other side). One-sided LBC does send the BinocularControl SYNCOFFSET flag in front of offsets. If you don't want the other side to wait for those LBC dither offsets, they need to be ignored on the IIF Control GUI (click the "Ignore" check box next to Offsets on the LBC side).

LUCI1 and LBC-Red in Binocular Mode

  1. Proceed with the LUCI1 observation as normal to send the preset to the new target (LUCI1 sends its own SYNCPRESET in advance of the preset command) .
  2. Play a trivial LBC OB that contains the coordinates of the same target (one-sided LBC sends its own SYNCPRESET in advance of the preset command).
  3. No additional presets are needed until it is time to move to a different target.
  4. As the LUCI1 observations proceed, make LBC-Red observations with DOFPIA and/or additional OBs (which have DEC=-90 so they won't send presets to move the telescope).

Small asynchronous offsets must remain within the co-pointing limit on each side. Large offsets (beyond the copointing limit) that need to be synchronized will require some additional manual intervention on the LUCI1 side (possibly sending the!BinocularControl SYNCOFFSET from the command line).

Why are MODS1 and LUCI1 different

(from Olga) To the observer and PI, LUCI+LBCR observations differ from MODS1 + LBCR observations in that they are true binocular, not pseudo-monocular, observations. That means that LBCR can not only guide while the left side is taking data, but can also dither.

In TCS terms, both LUCI1 and LBCR will send 'synchronous' presets. (MODS1 does not yet have the ability to send a 'synchronous' preset). Therefore, the LBCR OB to be used with MODS1 does not send a preset. On the other hand, the LBCR OB to be used with LUCI1 will need to be broken into two pieces, the first of which does send a preset (much like MODS1/LUCI1 acq and obs scripts).

MODS1 and LBC-Red in Binocular Mode

There are three ways to make this observation:

Option 1: Send Presets outside MODS1

  1. Send the telescope to the target with a pair of SYNC presets sent from either IRAF LBTtools or IDL. (The TO can easily do that from a pair of IRAF windows, but it requires the target to be in the LBT standard catalog list/format.)
  2. Proceed with the MODS1 observation as normal. It's even OK if MODS1 sends another asynchronous preset (within the copointing limit), since the telescope is already at the target.
  3. Proceed with LBC OBs that have DEC=-90 and therefore use the current target without sending a new preset. These LBC OBs can dither (within the copointing limit, and with SYNCOFFSET ignored on the IIFGUI -- see above).

Option 2: Manual BinocularControl Commands

  1. Send the left BincularControl SYNCPRESET command from the command line before you send the MODS1 preset.
  2. Proceed with the MODS1 observation as normal to send the preset (without additional BinocularControl) to the new target.
  3. Play a trivial LBC OB that contains the coordinates of the same target (LBC sends its own SYNCPRESET in advance of the preset command).


Option 3: Pseudomonocular Mode (described below)

Pseudomonocular mode for passive / parallel observations

We have implemented an additional "pure parallel" (HST parlance) or "symbiotic" mode where the unused-side of a monocular observation can be used to carry out an automated survey. This concept is known as "pseudo-monocular mode" where the "dominant" side instrument controls everything as if it were observing in "monocular" mode, and the "passive" side instrument goes along for the ride without the ability to send presets. Technical details are discussed in Issue 4513. Pseudo-monocular mode has the advantage that the "dominant" side observations are simple, and they work with pure monocular instrument software (i.e. MODS1). Any presets sent from the passive side are ignored with a warning. Passive side offsets can be either accepted or ignored (with a warning) depending on the state of the check box "Allow Offset" on the IIFGUI control form. Pseudo-monocular mode will work for LUCI/LUCI observations as long as the "Allow Offset" box is unchecked on the passive side (otherwise the TCS will get very confused). See for a full description.

Steps for Pseudo-monocular Observing

  1. Authorize the desired instrument on each side using the IIFGUI.
  2. Click the "PseudoMono" button on the IIFGUI Control page for the side which is to be "dominant".
  3. Uncheck the "Allow Offset" box on the passive side if you do not want passive side offsets acted on (i.e., for LUCI binocular scripts).
  4. Proceed with normal monocular observing on the "dominant" side (any presets or offsets will move both sides with the mount).
  5. Proceed with observing on the passive side. Any presets from this side will be ignored with a warning. Small offsets (< 5 arcsec) on the passive side within the copointing limit and guiding will work fine if the "Allow Offset" box is checked.
    (Olga tested this closed-dome on 20160506 UT. On-sky on 20160512 UT they found that LBC does not wait for large optics moves to complete. However, this should be fixed as of Sept-2016 - see: IT5715)

Passive LBC Images Automatically

JohnHill has written a python script which is able to automatically take LBC-Red images as the passive instrument with MODS1 or LUCI1. See /home/lbcobs/supportscripts/SymbioticSupport/ (with much documentation in the header of the script).

JohnHill has written another similar python script which will automatically loop through a series of LBC OBs and the passive instruments. For example you might want to loop through a series of filters or a series of exposure times. See /home/lbcobs/supportscripts/SymbioticSupport/ (with much documentation in the header of the script).
Example:  ./  -o 'num1.ob num2.ob num1.ob numb3.ob'
 (The quotes are needed when you specify the space-separated list.)
optional command line arguments
 -p [/pppp/, default=.] path to the OB files
 -t [x.xx, default=1.0] scaling of the OB exposure time
 -m [nn, default=100]   maximum number of times to play the OBs
 -d [ss, default=2]     sleep delay in seconds between commands
 -f [ff, default=1]     which OB in the list to start with
 -h or --help           print this help message


What happened?

Watch the IIFGUI for status flags and event messages while you are sending these presets. A voice alarm will inform you if any copointing or mirror travel limits have been violated.

How to get unstuck?

If you have the converse problem (where an instrument is sending SYNCPRESET or SYNCOFFSET BinocularControl flags when you don't want them), there are "Ignore" and "Release" buttons on IIF to control (all or one) of them.

-- %USERSIG{JohnHill - 2014-04-14}%
Topic revision: r19 - 22 May 2018, KelleeSummers
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