DIS III - Users Information

Contact Webmaster for web page errors, corrections, ommisions, and/or additions.

This page last updated: February 11, 2007 - GS
This page last checked: September 27, 2004 - JMD

Basic User's Guide: DIS - 2007

Contents

Instrument Description

Basic information to know...

DIS Slit Inventory

Using DIS with TUI

UsingDIS with Remark

Lamp Calibration Spectra with DIS

DIS Quick Start Guide (PDF)

DIS Slit Orientation Calculator Page (Maintained by B.Ketzeback)

Detailed Camera Documentation

DIS Operations Manual By Robert Lupton

DIS Gratings: Blaze angle and wavelength (Russet is this info obsolete???)

DIS III Slits - photos: March 5, 2002

Craig's COMMAND QUICK COMMANDS REFERENCE PAGE.

Craig's COMMAND QUICK KEYWORDS REFERENCE SHEET.

Jon Holtzman's report on first DIS II/III characterization (note that the blue chip has changed since this report!)

Vignetting

Setting Orientation of and Placing Objects on the DIS Slit

Instrument Description

The DIS (Dual Imaging Spectrograph) was built at Princeton by Jim Gunn, Michael Carr, Brian Elms, Ricardo Lucinio, Robert Lupton, and George Pauls. It is a medium dispersion double spectrograph, which can either be used in a direct imaging mode, or as a spectrograph.

The optical path consists of a slit-mask assembly, a shutter, a dichroic (with a transition wavelength of 5350 angstroms), and two independent collimators and cameras for the blue and red sides. The gratings and mirrors are mounted on a grating turret holding two mirrors (red and blue) and two sets of two gratings. The way that the CCDs are mounted results in the dispersion in the two chips running in opposite directions.

Because the dichroic is not in a parallel beam there is a ghost image on the blue side, produced by light reflecting off the back surface of the dichroic. It's displaced by about 20 pixels to the red. When the slit is illuminated with an He arc the amplitude is about 10%; inserting the g filter totally removes the ghost. We are considering coating the back of the dichroic to reduce this effect. When using the gratings, this ghost is of course dispersed off the chip. There are also ghosts when you are taking spectra; they will also be improved by AR coating.

When being used as a spectrograph, the entrance aperture can be either a long slit or a slit mask; the total slit length is 6', and up to 5 slits of various widths can be installed.  Currently there are several available slits at APO, or users may supply their own.

Two sets of default gratings are currently installed: a Red Medium/Blue Low and a Red High/Blue High. More detailed information on the gratings can be found here.

The shutter is a rotating half-circle; this means that there is no aperture correction, even for the shortest exposures.

The slit mask assembly contains five masks; of these the first usually contains a long slit, and the second is clear. The other three are available for other, or user created, slit masks. The slit masks can be changed by on-site personnel during the afternoon checkout. All other operations can be controlled by the remote observer.

The CCDs are cooled by closed loop CryroTigers. The cameras are both cooled to approximately -100 Celsius.

More detailed information can be found here.

Basic information to know...

You should retrieve your science images off from APO computers within 7 days after they are taken, otherwise they will be deleted. We DO NOT back up data locally here. Data can be found here.

Standard Default DIS III grating setup is - Red High/Blue High & Red Medium/Blue Low.

All grating configurations and wavelength centers need to be explicity stated in your proposal. Gratings setups different than the standard must be sent requested via separate e-mail to the techstaff at APO 2 days prior to your observing run.

Please state which gratings you wish to use (eg. DIS Red - Low, Blue - Low, not DIS Low resolution gratings) and the wavelength centers you wish.

If there is a grating setup different than the standard default setup then your program time will be used, if neccessary, to make the grating change and calibrations to/from the standard default setups. Please allow approximately 25 minutes for this. The observing specialist on duty that night can advise you if/when this will need to occur.

The following are the default wavelength centers that we use for our setup calibrations, If you wish a different wavecenter or grating set, Please inform your observng Specialist at least 1 day prior to your observing run.. This gives us time to install and/or calibrate the gratings to your specifications.

DIS Spectra (Dispersion, Waverange, and (default) Wavecenters) and Offsets

The grating centers are fairly stable once set, during the start of the night, and typically do not move during instrument rotations, However movement of the turret (changing from one set of gratings to the other) can cause a grating center shift and therefore you should always repeat your cals if the turret is moved.

Rotation does cause different illumination of mirror cover flats.

Shutter times of less than 3 seconds are not repeatable.

Click the sync button (Remark) or current button (TUI) to verify your gratings, grating centers, binning, and windowing are correct. If they are not, make necessary changes in Remark/TUI and click the apply button.

Rotating DIS with Remark

+ object rotation will rotate to the star to the E.

DIS Slit Inventory

NOTES: 'Locations' were as of October 2004. "DIS" refers to slits which remain permanently availablein the so-called default slit wheel. This 'default' wheel also contains one open position for imaging-mode observations.

Using DIS with TUI

• Configuring TUI to use DIS
• Setting up DIS exposure parameters
• Taking your Calibration lamps
• Taking your Dark Frames
• Focusing DIS
• Centering your star on the slit
• Changing the DIS guider filters
• Using the auto-guider
• Setting up multiple exposures
• Taking your exposure
• Pausing an exposure
• Stopping an exposure (early Readout)
• Stopping an exposure (discarding data)
• Where does your Data go?
• Always examine your data!

DIS Quick Start Guide (PDF)

DIS III - Advanced Usage Information

Detailed Camera Documentation

• Section 1 - Photos
• Section 2 - Assembly Drawings
• Section 3 - Detail Drawings
• Section 4 - Electronics
• Section 5 - Plenums
• Section 6 - Misc. Notes 1
• Section 7 - Misc. Notes 2
• Section 8 - Installation Measurements
• Section 9 - Other Docs, Data Sheets, and Certificate of Conformance

DIS: The Double Imaging Spectrograph

Overview:

1. The Double Imaging Spectrograph

1.1 Introduction

The DIS was built at Princeton by Jim Gunn, Michael Carr, Brian Elms, Ricardo Lucinio, Robert Lupton, and George Pauls. It is a medium dispersion double spectrograph, which can either be used in a direct imaging mode, or as a spectrograph.

This manual is written in a dialect of TeX, TeXinfo, and is also available as a printed document. You can either read it using an info viewer, or through WWW (e.g. xmosaic).

1.2 Description of Instrument

The optical path consists of a slit-mask assembly, a shutter, a dichroic (with a transition wavelength of 5350 angstroms), and two independent collimators and cameras for the blue and red sides. The gratings and mirrors are mounted on a grating turret holding two mirrors (red and blue) and two sets of two gratings. The detectors are a thinned, uv-coated SITe (formerly Tektronics) 512x512 CCD with 27 micro pixels on the blue side, and a thinned 800x800 TI chip with 15 micron pixels on the red side. The gain on the blue side is 0.96 electrons/DN; on the red side it is 1.47 electrons/DN; and the readnoise is about 9.5 electrons. The electronics on the blue side misbehave for very over-full wells; the signal is set to 0, and the pixels to the side of the offending pixels are also set to 0. The way that the CCDs are mounted results in the dispersion in the two chips running in opposite directions.

The collimator focal lengths on the blue and red side are both 963mm; the camera focal lengths are 140.3mm and 141.7mm on the blue and red sides respectively; the resulting reduction is 6.865 in the blue and 6.798 in the red (the measured values are within 1/2% of this value, and vary slightly with collimator focus). The measured scales are 1.086 arcsec/pixel in the blue and 0.610 arcsec/pixel in the red. The beam diameter is 100mm, and the angle between the collimator and camera optical axes is 35 degrees. There are commands to centre given wavelength on the chips.

Because the dichroic is not in a parallel beam there is a ghost image on the blue side, produced by light reflecting off the back surface of the dichroic. It's displaced by about 20 pixels to the red. When the slit is illuminated with an He arc the amplitude is about 10%; inserting the g filter totally removes the ghost. We are considering coating the back of the dichroic to reduce this effect. When using the gratings, this ghost is of course dispersed off the chip. There are also ghosts when you are taking spectra; they will also be improved by AR coating.

When being used as a spectrograph, the entrance aperture can be either a long slit or a slit mask; the total slit length is 6', and slits of width 1.5 and 1 arcsec are installed in slit mask wheels A and B in positions A1 and B1 respectively. In imaging mode the ends of the slit are at approximately (125,250.7) and (492,251.4) in the blue chip, and (120,433.8) and (775,434.2) in the red. At the time of writing, the FWHM at the centre of the slit are about 1.4 and 1.8 pixels.

Two sets of gratings are currently installed: a 150/300 lines/mm pair, and an 830.8/1200 lines/mm pair; the blaze angles are ??. All gratings are run in first order. The low-resolution pair have dispersions of 6.2 A/pix and 7.0 A/pix for the blue and red sides; the high resolution gratings' dispersions are thus approximately 1.1 A/pix and 1.7 A/pix to within a cosine. When used for imaging, the field of view is 4'x6'.

The shutter is a rotating half-circle; this means that there is no aperture correction, even for the shortest exposures.

The slit mask assembly contains five masks; of these the first usually contains a long slit, and the second is clear. The other three are available for user-created slit masks. There are two slit wheels, which can be easily changed by on-site personnel during the night. All other operations can be controlled by the remote observer.

The CCDs are cooled by liquid nitrogen. The cameras are automatically filled from a storage dewar when empty; provided that the storage dewar is pressurised and not empty, the cameras will remain cold. The red side runs at approximately -125 Celsius; the blue side at about -100 Celsius.

There are two optical systems that must be focused in a spectrograph, the collimators and the telescope. We do not expect users to have to focus the collimators (and it can't be done remotely in any case). The telescope is focused in the usual way. Because it is not yet possible to take multiple exposures, you will have to read out the DIS after each movement of the secondary.

There are a total of nine mechanisms that can be commanded remotely: the four grating angles (see section 1.3.6 Selecting Mirrors or Gratings, and Grating Tilts); the position of the grating turret (see section 1.3.6 Selecting Mirrors or Gratings, and Grating Tilts) and the detent (which we hereinafter ignore); the filter wheel (see section 1.3.4 Selecting a Filter); the slit-mask wheel (see section 1.3.11 Selecting a Slit Mask); and the shutter (See section 1.3.2 Taking an Exposure; see section 1.3.15 Homing the Shutter).

The computer systems used to run the DIS are typically baroque. The observer sends commands to a programme called the MC which is responsible for book-keeping and routing commands; in fact, there may well be another layer above the MC -- for example, I use mirella(1) to send commands to the MC, and others may use Bob Loewenstein's mac interface. The MC then passes the commands on to an instrument control computer (icc); in the case of the DIS this involves two more processes. The DIS icc is a PC, and it sends commands over an RS232 line to a TDS microcomputer that is physically on board the instrument.

1.3 Command Summary

All commands should be preceded by `dis', and all commands can be asked for help (e.g. dis grating help).

You should not attempt to send a second command to the DIS before a first has completed. The sole exception is expose, when it is safe to send commands after the shutter has been opened (the integrating for n seconds message). Commands return a completion code (of :) to the MC when they have finished.

If the instrument is power-cycled, all responses that it returns will include the remark, "spectrograph micros are not initialiased!". If you see this, you should use the init (see section 1.3.9 Initialising the PC and Onboard-Micro) to initialise things. This will also reset the nitrogen filltimes, a detail that will concern few observers.

Please note that, as of the time of writing, these commands had been used for nearly a week of `remote' observing. They are not well tested, and some of the MC-related parts still need work.

The available command are:

1.3.1 Hardware Control of the Cameras

camera [red|blue] prep

Prep the chips (i.e. read them to get rid of old and unwanted charge). If you don't specify a colour (or specify both) both chips are prepped. The chips are automatically prepped before each exposure.

 

camera skiplines=n

Read out n lines and throw the data away. This is most often used for focussing.

 

camera status

Print some status information for the cameras.

 

camera wipe[=on|off]

Continuously read the chips until told to stop with camera wipe=off.

This command should always be used while the chips are cooling, as it gets trapped charge out of the oxide layer.

 

1.3.2 Taking an Exposure

The expose commands are used to take data and transfer it to the Unix host, currently tycho. At present the files have minimal headers and appear by default in the directory `/export/home/dis/data'. The file format can be either Mirella (the default) or FITS (see section 1.3.5 Specifying the File Format).

Header keywords are described below, See section 1.7 Keywords in DIS Disk Files..

As explained above (see section 1.3.3 Specify the Output File), the DIS usually puts files in a well-known place on the unix host, expecting the MC to massage them suitably (e.g. adding RA and dec to the headers) and safely archiving them somewhere. Until this is done, we have added a temporary command file and an option to the expose command to choose file names.

If you don't use these facilities, mirella format files are called `dispic_b.hdr', `dispic_b.img', `dispic_r.hdr', and `dispic_r.img' for the blue and red images respectively. These files are very close to IRAF 2-file formats (.img files are identical to .hhd; .hdr and .hhh are the same to within whitespace); nonetheless without some massage IRAF cannot handle these files, and you should proceed to the next paragraph.

FITS files are called `dispic_b.fts' and `dispic_r.fts' for the blue and red images respectively.

These files are overwritten everytime that you take an exposure! You are responsible for saving them. If you are using the mirella interface there are words to do this for you -- ask RHL for details.

expose abort

Abort an exposure, either in progress or already stopped (with expose pause).

 

expose help

Provide a summary of expose options.

 

expose pause

Pause an exposure, i.e. close the shutter but don't read the chips. You can resume the exposure later; abort it, or read the data.

 

expose read [bin] [red[=0|1]|blue[=0|1]] [old]

Read an exposure; either one that you paused or one that is in progress that you'd like to halt prematurely. If you want to abandon an exposure entirely, use expose abort.

You can specify which chip to read and the desired binning; if you don't specify anything the values used to start the exposure will be used. The arguments are discussed in more detail under dis expose time=n

You can also read an exposure that has already finished (or even one that has been aborted, but about which you've had a change of heart). This is slightly dangerous, as if a chip has already been read reading it again will replace your data with a bias frame. In consequence, you must explicitly specify the old flag if you want to read chips after an exposure has been completed; in addition the way that colour flags is interpreted is a little different. If you omit a colour specification neither chip will be read -- the chips specified in the original expose command are ignored. The same goes for binning; if you want the data binned you must explicitly say so.

 

expose resume [bin] [red[=0|1]|blue[=0|1]] [time=t]

Restart a paused exposure. You can specify which chip to read and the desired binning; if you don't specify anything the values used to start the exposure will be used.

The arguments are discussed in more detail under dis expose time=n

If the time specified is different from the original exposure time the integration time will be adjusted (although the total time may differ from that requested by up to half a second); if it is shorter than the time already elapsed the chip will be read immediately.

 

expose status

Report on exposures in progress or recently completed.

 

expose [bin] [dark] [file=name] [red[=0|1]|blue[=0|1]] bias|time=t|snap

Actually start an exposure. The time is in seconds and must be provided. If you specify 0, a snapshot will be taken (snap is an alias). This is the shortest exposure possible, and opens the shutter for 0.6s. If you specify bias instead of time a bias frame will be taken; if you specify dark (as well as a time) a dark frame will be taken.

Optional arguments are:

 

bin[=0|1]

Bin the data 2x2.

 

dark

Don't open the shutter, but thus take a dark frame.

 

file=name

Write the data to files named `name_b' and `name_r' on the unix host. As an alternative, consider the file command (see section 1.3.3 Specify the Output File); this flag overrides any filename specifications made there (but it obeys any dir=name settings).

 

red[=0|1]|blue[=0|1]

Only read the red or blue chip. If you don't specify a colour, both are read. If you don't specify a value it defaults to 1, meaning that that colour should be read.

 

 

1.3.3 Specify the Output File

The file commands should only be used if you are directly commanding exposures with dis expose.

It is not the job of an instrument control computer to decide where to put datafiles on the unix host; it is the job of the MC -- which should know almost nothing about the instrument. At present at APO the MC is structured to make this difficult, and therefore as an interim measure the I have added the commands in this section. There is also an interim flag, file that expose (see section 1.3.2 Taking an Exposure) understands.

You can specify a filename, e.g. `ngc6205', or request the DIS to generate names for you; in this case you can specify the base part (e.g. `bias') and the starting record number (e.g. 100), in which case files will be named `bias00100', `bias00101', `bias00102', and so forth. The red and blue sides are distinguished by having a `_r' or `_b' appended, so if you are using FITS format (as specified using the format command (see section 1.3.5 Specifying the File Format)), the next red file would actually be called `bias00103_r.fts'.

No attempt is made to ensure that the file doesn't already exist on the unix disk! Caveat scrivor.

file auto[=on|off]

Name datafiles with a unique record number, which is automatically increased after each exposure. If you specify off, this is (of course) disabled.

 

file dir=name

Place the files in the directory name on tycho. If name doesn't start with a / it is interpreted relative to `~dis'. The directory must be writeable by the dis account.

 

file file=name

Call the output file name. If auto is turned off, this is equiavalent to specifying file=name to expose, but if you are using the automatic generation of filenames, it is used as the base part of the filename.

 

file recnum=####

The recordnumber for the next automatically generated filename is set to ###.

 

file status

Report the current status of filename generation

 

1.3.4 Selecting a Filter

Both the keywords filter and filters are accepted.

filter 1

filter clear

Put in the clear filters. Actually there are no filters at all in this position.

 

filter 2

filter gr

Put in the real filters; Gunn-Thuan g and r on the blue and red sides respectively.

 

filter home

Home the filter wheel (to the empty position).

 

filter status

Inquire the status of the filter wheel.

 

1.3.5 Specifying the File Format

The format commands should only be used if you are directly commanding exposures with dis expose.

The DIS can currently write files on the unix host in either Mirella or FITS formats. The Mirella format is very similar to IRAF, but apparently not quite identical. At some point, quite soon now, the files will be written using standard APO procedures.

format fits

Write files in FITS (`*.fts') format.

 

format mirella

Write files in mirella (`*.{hdr,img}') format.

 

format status

Report the file format that the DIS is currently using.

 

1.3.6 Selecting Mirrors or Gratings, and Grating Tilts

Commands to select gratings or mirrors, and manipulate the grating tilts. gratings or turret is acceptable as an alias for grating.

It takes about 50 seconds to switch between the high resolution and the low resolution gratings; about 30 seconds to go from grating set 1 to the mirrors; and about a 100 seconds to change from grating set 2 to the mirrors. When you tilt the gratings they are first homed, to avoid problems with missed steps, and it takes about 30 seconds to go from step 2100 to step 2101 (a wavelength of about 1.2 microns for the high resolution red grating; about 6.8 microns on the low resolution side). Times for more moderate tilts are somewhat shorter.

grating 1

Select grating set 1, currently the low-resolution (150/300 lines/mm)pair.

 

grating 2

Select grating set 2, currently the high-resolution (830.8/1200 lines/mm) pair.

 

grating change1

Move the turret to the correct position to change grating set 1.

 

grating change2

Move the turret to the correct position to change grating set 1.

 

grating home

Home the grating turret after a crash or other problem, and home all the gratings. Use ghome to home an individual grating.

 

grating col=[r|red|b|blue] n=[1|2] [lambda=l|step=n]

Set a given grating to a given position. You can either specify a step or a wavelength (in angstroms) to set at the centre of the chip. The n refers to the grating pairs. Most users will not want to use the step form, as it requires a familiarity with the stepping motors used to tilt the gratings.

 

grating col=[r|red|b|blue] n=[1|2] ghome=1

Home a specified grating.

 

grating ok

Tell the DIS that the gratings that it thinks are in the turret are indeed the ones loaded. You need to issue this command after the grating turret door has been opened. If you changed any gratings it is your responsibility to update the DIS's idea of grating parameters; as there are currently only two sets of gratings available, there is no way for naive users to do this.

 

grating status

What is the status of the gratings and turret?

 

1.3.7 Getting a Summary of Options

help

Print a help message. Note that all commands accept help as an option, e.g. dis gratings help.

1.3.8 Homing all Mechanisms

home

Send all the mechanisms home; you'll have to init (see section 1.3.9 Initialising the PC and Onboard-Micro) the DIS first. You will have to home the instrument after powering up the micro, and after the TDS micro on the instrument has crashed. You can restore the instrument to the state it had before the crash with the tds command (see section 1.3.18 Recovering from TDS Problems/Reboots).

1.3.9 Initialising the PC and Onboard-Micro

init

Initialise the instrument computers. You'll have to do this before you can do anything else. If the spectrograph micro has crashed, you'll have to home everything before you can send mechanisms such as gratings to specified positions (see section 1.3.8 Homing all Mechanisms).

1.3.10 Liquid Nitrogen Commands

Control or inspect the liquid nitrogen system. The dewars run at liquid nitrogen temperatures (78K), the blue camera runs at about -100C, and the red camera at about -125C.

ln2 cool=t

Keep the nitrogen system on until the dewar temperatures reach some predetermined value (currently 85K). The command will keep trying for t minutes before the desired temperature is reached or it gives up. Don't give it too long a time -- if the supply dewar is empty you'll have lost control of the instrument until the time finally elapses (or until someone at APO hits ^C on the PC running the instrument). We start the CCDs wiping for you.

 

ln2 off

Turn nitrogen filling off. The chips will eventually warm up.

 

ln2 on

Turn the nitrogen system back on.

 

ln2 status

What is the status of the LN2, and the temperature of the chips?

 

ln2 top

Force a nitrogen fill (top up the dewars).

1.3.11 Selecting a Slit Mask

Control the slit mask assembly.

mask 1

mask slit

Select mask 1, which should be a long slit.

 

mask 2

mask clear

Select mask 2, which should always be empty.

 

mask 3

Select mask 3.

mask 4

Select mask 4.

mask 5

Select mask 5.

mask home

Home the slit mask wheel.

mask status

Where is the mask wheel?

1.3.12 Inserting the Mirrors

mirrors

Put in the mirrors.

There is an optional argument:

 

[home]

Send the grating turret home.

1.3.13 Seeing if all Computers are Alive

ping

Request each of the many computers in the chain of command to acknowledge their existence. If all is well you'll get a Descartian assertion from the forth TDS micro on the spectrograph.

1.3.14 Set a Special MID for `Orphaned' Messages

The casual user can probably safely ignore this command.

set-special-mid

Set a special MID to receive messages from the DIS that are not associated with any known MID, such as device timeouts (and also syntax errors -- don't ask why they end up MID-less).

Mirella users can use the word init-dis to initialise the DIS and set the special MID with one simple, easily typed, word.

1.3.15 Homing the Shutter

shutter home

Home the shutter.

 

shutter status

What is the shutter status?

 

1.3.16 Finding the Status of the Hardware

status devices

Report the status of all the mechanical parts of the spectrograph.

 

status version

Report the version of the code on the TDS micro.

 

1.3.17 Syncing the MC with the PC

This command is not currently available. It shouldn't be needed.

sync

If the client appears to be totally confused over how to talk to the MC, this command should fix things up.

1.3.18 Recovering from TDS Problems/Reboots

The DIS remembers the status of the instrument micro, the TDS. You can use this command to inquire what it thinks its status should be, or reset it to that status. We expect this to be used as

dis status
dis init
dis home
dis tds status
dis tds restore
         

1.4 Getting Started with the Instrument

As a zeroth step, logon to some machine that can communicate with the MC; for example if you are at APO logon to tycho and start the MC command line interface. If you are indeed using the raw MC interface (as opposed to, for example, the mirella interface) you may well want to start a dis window -- open a window (an xterm or shelltool) and type ~apotop/bin/dis-window &.

First check that you can communicate with the instrument:

dis ping
         

COMPUTO ERGO SUM !
         

Next, you'll have to initialise things. Try the command

dis init
         

dis home
         

Everything should be ready to go. See where things are:

dis status
         

dis ln2 status
         

You shouldn't have to focus the instrument, which is fortunate as doing so is impossible for the remote user. To focus the telescope you can either take a number of exposures, reading the chip between each; or close the shutter as you move the focus and telescope, finally reading the chips; or close the shutter and clock some charge as you move the focus.

To take four exposures without reading the chip, but moving the image by 15 lines in the blue and 22 lines in the red between exposures, say

dis mirrors
dis mask clear
  (set initial focus position)
dis expose red=0 blue=0 time=10
dis camera blue skiplines=15
dis camera red skiplines=22
  (change the focus)
dis expose red=0 blue=0 old time=10
dis camera blue skiplines=15
dis camera red skiplines=22
  (change the focus)
dis expose red=0 blue=0 old time=10
dis camera blue skiplines=30
dis camera red skiplines=44
  (change the focus, note that we skipped double before the last exposure)
dis expose old time=10
         

As an alternative, the final dis expose old time=10 could be written as dis expose red=0 blue=0 old time=10 like the other exposures, followed by dis old bias which has the effect of reading the chips; the initial exposure could be replaced by dis red=0 blue=0 bias to initialise the exposure, followed by dis expose red=0 blue=0 old time=10. If you follow both these pieces of advice all of the `real' expose commands are identical, which means that you can put them in a loop ....

You'll need to find where the slit is; if you aren't using custom multi-slits, you'll want to use the slit in mask position 1; you can refer to this as either dis mask 1 or, as here, by name:

dis mirrors
dis mask slit
dis expose time=30
         

Next acquire a target (I'll assume that a 10s exposure is enough); to save time let's only read the red chip:

dis mask clear
dis expose time=10
         

dis format fits
         

Next, slew the telescope to put the image where the slit is, put the slit back in and see if the target falls on it:

dis mask slit
dis expose red=1 time=30
         

dis gratings 1
dis gratings col=blue n=1 lambda=4400
dis gratings col=red  n=1 lambda=7700
dis expose time=100 file=my_first_spectrum
         

Note that we explicitly specified that the data be saved as `my_first_spectrum' -- this means as files like `my_first_spectrum_b.fts'. You can't simply repeat the command using some history mechanism as your second spectrum would overwrite your first, so you have to remember to specify unique file names. Another way to proceed is to ask the DIS to think of names for you. For example, to use a set of filenames of the form `R00000', `R00001', and so forth you'd say

dis file file=R recnum=1 auto
         

When you come to take arcs, arrange for someone on the mountain to attach an arc to the front of the telescope and turn it on. We've had success with an Hg/Ar arc and 100s exposures with the low resolution gratings. Incandescent flats are acquired in a similar way. As I type this (within an hour of the 1st of October 1994) Jim is drilling holes in pieces of aluminium trying to make arcs and flats remotely operable.

1.5 Comparison Spectra -- Taking and Interpreting

Currently (1st October 1994) we can nearly, but not quite, control the arc and flat field lamps mounted on the secondary from the telescope.

Eventually we expect to provide detailed plots and line lists, but for now all that we have is one low resolution spectrum of an Ar-Hg lamp. Unfortunately, TeXinfo cannot display graphs.

1.6 Interactions with the MC

The DIS has been used from Robert Lupton's mirella interface to the telescope. Your mileage may vary (including changing sign) if used in other ways.

You should be able to send the DIS commands from the MC by prefixing your command strings with dis; if you are talking to the MC perl directly, response strings will come back via the mc-window as usual. If you are using RHL's mirella interface, responses to commands are sent back from the MC on the same MID as they were sent on.

In addition, all DIS messages are sent to a special distributed class called dis, which you can subscribe to like any other class.

Messages that correspond to no known MID, such as device timeouts, are also sent to class dis, prefixed by the string Orphan text:. Alternatively, you can use the DIS command set-special-mid (see section 1.3.14 Set a Special MID for `Orphaned' Messages).

1.7 Keywords in DIS Disk Files.

The state of the instrument is given in the header; keywords are:

CCDNUM

1 for the blue chip; 2 for the red chip.

 

EXPOSURE

Length of the exposure in seconds. If you have paused and restarted the exposure the value may be incorrect by up to half a second. If the exposure time is negative the shutter was not opened, and you have a dark frame. Bias frames have exposure times of 0 (which isn't really a special case).

 

FILTER1

Which filter is in; FILTER0 (empty) or FILTER1 (Gunn-Thuan g/r).

 

FILTER2

Always EMPTY (there is only one filter wheel).

 

GLAMBDA1

GLAMBDA2

GLAMBDA3

GLAMBDA4

The position of the four gratings (B1, R1, B2, and R2) in Angstroms. The values are only approximate, and are derived from the values of GSTEPn.

 

GRATING1

GRATING2

GRATING3

GRATING4

Identification strings for the four gratings, consisting of lines:blaze where lines is the number of lines/mm for the grating, and blaze is the wavelength (in Angstroms) of the blaze.

N.B as of early June, the blaze wavelengths were not known.

 

GSTEP1

GSTEP2

GSTEP3

GSTEP4

The position of the four gratings (B1, R1, B2, and R2) in units of steps of the stepping motors.

 

MASK

The number of the current grating mask.

 

TIME

Ending time of the exposure in UT.

 

TURRET

The position of the grating turret, e.g. MIRRORS.

1.8 What To Do if there are Problems

A multitude of things can go wrong with the instrument, so your problem is probably not discussed here. Still, it might be. If you think that it might help you can try calling RHL at work (609-258-3811) or at home (609-466-2431); JEG's numbers are 609-258-3802 and 609-924-1304 respectively. You had better think hard before calling us at home, and please remember that there is a two hour time difference from APO.

Can't ping the instrument.

There are four places that this command might fail, each further into the depths of the system than the last:

No reply

This means that the MC isn't responding. This isn't a DIS problem at all, so I am afraid that all that I can suggest is the usual sequence of kills and restarts.

 

Only the MC is alive message

This means that the client that communicates between the MC and the instrument isn't running (either never started or dead), or is non-responsive. If mc status thinks that the dis_s isn't running, start it (starticc dis) and try again. If that doesn't help, kill all the processes that are connected with the client and then try starting it; you can do this with the unix command /home/apotop/start-dis -r (if you want to issue the command from the mc you'll need to preface it with a !). From the mirella interface you can restart things with the command restart-dis-icc. This litany may not work if the MC or Hub is playing up; in this case intersperse start-dis -r commands with the usual MC black magic. You will need to set the special MID used for orphaned messages (see section 1.3.14 Set a Special MID for `Orphaned' Messages).

 

Only the MC and Client is alive messages

This means that the DIS's PC isn't responding. Get someone at APO to go and look at the PC. Ask them to type host; if that works (i.e. there are no complaints) then Mirella is up and in a suitable state. If it doesn't, the simplest thing to do is to reboot the machine -- press the three keys ALT-CTRL-DEL all at once (DEL is the keypad .). If that doesn't do anything, press the white button on the front panel. Does host work now? If not, proceed to check the cabling.

 

Only the MC, Client, and Mirella is alive messages

The instrument micro is down, or communications are confused. Eventually the latter condition (should) timeout, so go and reboot the micro (the easiest and best way is turn off the power to the electronics box. Not the power to the whole instrument.) You may have to play with the baudrate of the connection (see next item). If that doesn't work, try rebooting the PC (see previous paragraph). Can you ping it now? If not, check the cables, and then give up.

 

 

The PC can't talk to the TDS after a power-cycling

We usually run the serial line to the TDS at 2400, but it comes up at 9600, so after the TDS is power-cycled there's an inconsistency. Say:

ndis 2400 setbaud

to fix it. You may have to repeat this command a few times, and wait for various errors to timeout on the PC. Eventually you should get a message

I trying 9600 baud...

followed by no error messages (if you use setbaud a second time the success message will be I trying 2400 baud...).

 

The mirrors or gratings won't move.

Try power-cycling the logic box on the DIS (that's the one with the smaller power switch).

 

Images from the DIS are all zeros

The first thing to check is that the data coming from the instrument is zeros. Type

dis camera prep

and go and look at the DIS PC. The left hand column of numbers is a counter; the rest reflect the data coming from the chips. You can examine just one chip with

dis camera blue prep

or

dis camera red prep

If the data is all zeros, the problem is probably either in the PC or the onboard micro, or in the cabling. Try power-cycling the PC (push the reset button on the front panel). If this doesn't help, power-cycle the logic box on the instrument (the one with the smaller power switch). Then check the coax cables. Then talk to Jim Gunn.

 

The DIS doesn't seem to understand commands

For example, it might reply pre-ping ? to a dis ping command. This is caused by mirella on the PC getting stuck in an inappropriate vocabulary. Usually repeating the command will fix it (in fact repeating any command -- I usually use dis ping).

 

1.9 Notes for Expert Users

Are you sure that you should be reading this?

1.9.1 Sending Commands Directly to the DIS PC

Usually commands sent to the PC are mangled into a suitable form; You can disable this with the DIS command set-passthrough, and re-enable it with set-nopassthrough. So you can set the serial port timeout to 5 seconds on the PC with the commands

dis set-passthrough
dis 5000 serialtimeout !
dis set-nopassthrough
         

If you use mirella, this is done for you by the command ndis:

ndis 5000 serialtimeout !
         

It is possible to use this facility to cut yourself off from the instrument, for example

ndis bye
         

1.9.2 Sending Commands Directly to the Onboard TDS micro

The PC can send commands to the TDS, so once you know how to send un-mangled commands to the PC you are almost there (see section 1.9.1 Sending Commands Directly to the DIS PC). The litany on the PC is:

" command" >micro ct
         

ndis " DOORRESET" >micro ct
         

ndis 1 ?P
         

1.9.3 How to Reboot the Computers

It is possible to reboot either of the computers remotely, but it may not be a good idea. If you insist, the PC can be rebooted with

ndis % c:/bin/rebootb c
         

ndis " COLD" >micro ct
         

1.9.4 System Parameters on the DIS PC

There are times when you might want to change the code that runs on the PC, for example to temporarily change the number of lines/mm for a grating.

The PC is programmed in forth (well, actually it is running mirella but you won't be changing any C), so any changes that you have to make will involve typing (trivial) forth commands; for example the command

30000 serialtimeout !
         

serialtimeout ?
         

Variables that you might be interested in are:

Grating Lines/mm

There is an array called lines/mm with the values for the four standard gratings. To set the value for the 2nd grating to 1234.5 say 1234.5 4 lines/mm f!; print it with 4 lines/mm f?. Note that the number must contain a decimal point, and that you use f! and f? rather than ! and ?.

 

Grating Zero Points

The zero-point positions of the gratings are stored in an array called zero_order. These are the values in steps for the stepping motors that control grating tilt that put the zero-order image of the slit into the centre of the chip. They are used when you specify a wavelength to the grating command. The value for the third grating could be set to 100 with the command 100 3 zero_point !, and inspected with 3 zero_point?.

 

Serial Timeout

The RS232 line to the instrument from the PC times out after serialtimeout milliseconds. The default is 30000ms, if you wanted to set it to a minute you'd send the command 60000 serialtimeout !; to print the current value

 

Unix Host

The machine that images are transferred to is given by the variable unixhost, and the directory (relative to the home directory of the dis user account) by unixdatadir. You could set the host with " kepler" unixhost cs!, and print the current value with unixhost ct; how to set unixdatadir should be obvious. If you fiddle with these value you will have to ensure that the .rhosts files are set up correctly to allow the user dis on the machine dis to transfer files.

 

Verbosity

If the variable verbose is 1 some extra chatter is produced (e.g. a message that commands have been received).

 

1.10 Keywords Passed to the MC's dis Subscription

The DIS passes information to the MC in the form of messages prefixed by diskeys=. These are intended to allow the MC to maintain a mirror of the DIS's current state; currently they are merely passed out on a subscription called dis, along with all other DIS output. You can view them in a unix window with the command

dis-window | sed -ne "s/.*ys='\(.*\)'*/\1/p"
         

A given diskeys string may contain a number of white-space separated keywords; if values are provided and contain whitespace they are quoted with ".

The following list is complete at the time of writing (30th September 1994):

directory=name

Name of directory on unix host where data will be stored.

 

expose:abort=true

An exposure has just been aborted

 

expose:dark

This is a dark exposure.

 

expose:finished=true

The current exposure is finished.

 

expose:none=true

No exposure is in progress (the result of a query).

 

expose:paused=true

The current exposure is paused.

 

expose:resumed

The current exposure has just been resumed.

 

file:auto=off

Automatic generation of filenames is turned off.

 

file:auto=on

Automatic generation of filenames is turned on.

 

file=name

The next date file will be called name.

 

filter=name

The current filter is name (one of Empty, Gunn-Thuan gr, and Unknown).

 

format=type

The current file format is type (one of Mirella or FITS).

 

grating:Name:lambda=####

The approximate central wavelength for the grating is ####A. Name is The name of a grating, e.g. GR1 for the red grating in set 1.

 

grating:Name:step=####

The stepping motor position for the grating is ####. Name is The name of a grating, e.g. GB2 for the blue grating in set 2.

 

ln2:blueCam=###C

The temperature of the blue camera in C (as specified in the keyword).

 

ln2:blueFill=true

The blue dewar is filling.

 

ln2:blueLn2=###K

The temperature of the blue dewar in K (as specified in the keyword).

 

ln2:elapsedTime=time

The time since the last nitrogen fill cycle.

 

ln2=off

The nitrogen fill system is turned off.

 

ln2=on

The nitrogen fill system is turned on.

 

ln2:redCam=###C

The temperature of the red camera in C (as specified in the keyword).

 

ln2:redFill=true

The red dewar is filling.

 

ln2:redLn2=###K

The temperature of the red dewar in K (as specified in the keyword).

 

ln2:topping=true

The dewars are being topped off.

 

mask=#

The number of the current mask (1--5). As noted above, a slit should always be in mask 1, and mask 2 should be clear.

 

mask=invalid

The current mask position is invalid.

 

receptive=false

The DIS will accept no more commands until the current exposure is over (it will enforce this -- this keyword is just for your information).

 

receptive=true

During an integration the DIS can accept commands; this keyword means that it's ready to accept them now.

 

shutter:fault=true

An enquiry as to the shutter's status reveals a fault.

 

shutter=closed

The shutter is closed.

 

shutter=open

The shutter is open.

 

status=powercycled

The TDS has been powercycled.

 

status=uninitialised

The PC has not been initialised.

 

tds:date=str

The TDS status information was recorded at time str.

 

tds:filter=#

The TDS status information indicates that filter # was in use.

 

tds:grating1=#

The TDS status information indicates that grating 1 was at step #.

 

tds:grating2=#

The TDS status information indicates that grating 2 was at step #.

 

tds:grating3=#

The TDS status information indicates that grating 3 was at step #.

 

tds:grating4=#

The TDS status information indicates that grating 4 was at step #.

 

tds:mask=#

The TDS status information indicates that mask # was in use.

 

tds:turret=#

The TDS status information indicates that the grating turret was at position #.

 

time:elapsed=###

The time remaining in the integration (can be greater than the total length if the enquiry comes after the shutter is closed).

 

time:remaining=###

The time remaining in the current integration.

 

time:specified=###

The specified integration time.

 

turret:door=open

The grating turret door is open.

 

turret:door=wasopen

The grating turret door has been opened.

 

turret=name

The turret is at position name; possibilities are grating1, grating2, mirrors, change1, change2, and unknown.

 

version=str

Return the version string from the TDS. Each line of the original multi line string is separated by ||.

 

wipe=off

The chips are being wiped.

 

wipe=on

The chips are not being wiped.

 

1.11 Things on RHL's stack

• The headers are vestigial (actually, the other entries are never created). This has been somewhat improved (16th May 1994) but is still not ideal.

   

• The text in the dis distributed window gets truncated by the MC.

   

1.12 Things that have changed

21st April 1994

Added format command to support writing FITS files.

 

22nd April 1994

The lost message problem is under control. You can either get them directly (see section 1.3.14 Set a Special MID for `Orphaned' Messages), or subscribe to class dis. For details, See section 1.6 Interactions with the MC.

 

25th April 1994

Monitor the turret grating latch, and invalidate grating parameters if the door has been opened.

Look at the claimed position of the gratings to see if the TDS micro has been power-cycled.

Added the tds command to restore the spectrograph to a saved state.

 

26th April 1994

Measured zero-points of high resolution gratings.

 

16th May 1994

Fixed the stepping motor problems; this was the problem that was giving us trouble with grating tilts. It is not clear if the grating zero points are correct.

 

16th May 1994

Put DIS status information into the headers.

 

10th-12th June 1994

Changed directory names from gunnspec to dis.

You can now read the other chip after expose red=1 ....

pause/read/resume seem to work. You can specify a new time, binning mode, or selection of chips to read.

You can clock the chips some number of lines, (camera skiplines) permitting focus frames. An example is in the cookbook.

You can take bias and dark frames.

The selection of grating tilt by central wavelength now works correctly.

The camera cont has been replaced by camera wipe, which can be turned off.

Added aliases for time=0 (snap), mask 1 (mask slit), and mask 2 (mask clear).

Wrote lots of Cunning forth for mirella users (e.g. to take a set of spectra with the high resolution gratings that cover the entire spectral range of the instrument).

 

28th September -- 1st October 1994

Recovered from the lightening strike that destroyed the DIS's PC.

Installed the filters (only the g, but the r as added a day or two later).

Added the file command to specify where the datafiles should be put. This is a temporary measure.

Added a file=name command to expose. Also temporary.

Made the DIS report its status on the dis subscription stream, preceeded by `diskeys='. This is intended to make life easier for Bob Loewenstein.

The gratings are now always homed before being tilted.

More Cunning forth, of course.

 

31st May -- 1st June 1995

Fixed floating point stack overflow bug

An expose abort command now returns an error completion for the original expose command.

Reset the grating zero points to requested wavelengths should once more be correct.

 

Footnotes

(1)

mirella is a C and forth image processing system that Jim Gunn and I use. We run it on the DIS's icc PC, and as a command language to observe at APO (as well as for scientific analysis)

Table of Contents

• 1. The Double Imaging Spectrograph
  
  • 1.1 Introduction
    1.2 Description of Instrument
    1.3 Command Summary
    
    • 1.3.1 Hardware Control of the Cameras
      1.3.2 Taking an Exposure
      1.3.3 Specify the Output File
      1.3.4 Selecting a Filter
      1.3.5 Specifying the File Format
      1.3.6 Selecting Mirrors or Gratings, and Grating Tilts
      1.3.7 Getting a Summary of Options
      1.3.8 Homing all Mechanisms
      1.3.9 Initialising the PC and Onboard-Micro
      1.3.10 Liquid Nitrogen Commands
      1.3.11 Selecting a Slit Mask
      1.3.12 Inserting the Mirrors
      1.3.13 Seeing if all Computers are Alive
      1.3.14 Set a Special MID for `Orphaned' Messages
      1.3.15 Homing the Shutter
      1.3.16 Finding the Status of the Hardware
      1.3.17 Syncing the MC with the PC
      1.3.18 Recovering from TDS Problems/Reboots
      

    1.4 Getting Started with the Instrument
    1.5 Comparison Spectra -- Taking and Interpreting
    1.6 Interactions with the MC
    1.7 Keywords in DIS Disk Files.
    1.8 What To Do if there are Problems
    1.9 Notes for Expert Users
    

    • 1.9.1 Sending Commands Directly to the DIS PC
      1.9.2 Sending Commands Directly to the Onboard TDS micro
      1.9.3 How to Reboot the Computers
      1.9.4 System Parameters on the DIS PC
      

    1.10 Keywords Passed to the MC's dis Subscription
    1.11 Things on RHL's stack
    1.12 Things that have changed
    

Short Table of Contents

About this document

This document was generated on June, 5 2000 using texi2html

The buttons in the navigation panels have the following meaning:

where the Example assumes that the current position is at Subsubsection One-Two-Three of a document of the following structure:

• 1. Section One
  • 1.1 Subsection One-One
    • ...
  • 1.2 Subsection One-Two
    • 1.2.1 Subsubsection One-Two-One
    • 1.2.2 Subsubsection One-Two-Two
    • 1.2.3 Subsubsection One-Two-Three     <== Current Position
    • 1.2.4 Subsubsection One-Two-Four
  • 1.3 Subsection One-Three
    • ...
  • 1.4 Subsection One-Four

DIS Gratings: Blaze angle and wavelength - November 2000

High Resolution gratings

Red
Wavelength: 8465 Angstroms
Angle: 20.57 degrees

Blue
Wavelength: 5000 Angstroms
Angle: 17.45 degrees

Medium Resolution gratings

Red
Wavelength: 7500 Angstroms
Angle: unknown

Blue
Wavelength: 4000 Angstroms
Angle: 6.9 degrees

Low Resolution gratings

Red
Wavelength: 8000 Angstroms
Angle: 3.43 degrees

Blue
Wavelength: 4224 Angstroms
Angle: 3.63 degrees

DIS III Slits - photos: March 5, 2002

The New DIS Stainless Steel Slits

Vignetting

Old Optics VIGNETTING! Here is a plot!!

New Optics VIGNETTING! Here is a plot!!

Setting Orientation of and Placing Objects on the DIS Slit

1. Slew to field at Object Rotation=0, take a slit image.

    

2. If one or both of the objects are obscured by the slit, DO NOT offset at this time. You can adjust the position a little and reslew to get them off the slit. But offsetting before adjusting the rotation can make trouble.

    

3. Measure the positions of the two objects: (x1,y1) and (x2,y2)

    

4. Rotate to this angle:

    

                             / (y2 - y1) \
                     arctan ( ----------- )
                             \ (x2 - x1) /
      

   
   If I got this right, the sign of the rotation should come out correct. You can also check it visually: A positive rotation moves the field clockwise.

    

5. After rotating, take another image to verify that the rotation is correct, and find the offset position to get them on the slit.

    

6. Use an instrument offset to move the two objects onto the slit.

    

SETTING OBJECT(S) OF A GIVEN POSITION ANGLE ONTO THE SLIT

If you know the P.A. (Position Angle) of your object on the sky, you can place it on the slit by using the following rotation:

Rotation = (P.A. - 90)

Where P.A. is measured North through East on the sky, North= 0 and East=+90. This rotation will align the object(s) parallel to the slit. Use an instrument offset in the Y direction to move the object(s) onto the slit. The pixel scale can be found here.

SETTING SLIT TO BE PERPENDICULAR TO HORIZON:

If your goal is to orient the slit with respect to the horizon, there are two ways to go about it. The simplest is to use a rotation type of horizon. To keep the slit perpendicular to the horizon while you track, set the rotator to 90 degrees, horizon. The drawback to this method is that the field is no longer de-rotated on the sky. Thus only one point in the field will be stationary and all else will rotate about it. This point is called the boresight. To minimize the rotation of your object, you should correct local pointing error (Recalibrate under Telescope -> Special Moves) then use object offsets to put your object at the center of the slit.

A few words on offsets:

The reason you need to use object offsets to place the object at the center of the slit (defined as the boresight in the instrument block)is because object offsets leave the boresight at its default location. Instrument plane offsets move both the object and the boresight. Thus, while you may put your object in the center of the slit using instrument plane offsets, you will have moved the boresight away from the center of the slit at the same time. Again, Object plane offsets only move the object. Instrument plane offsets move both object and boresight. The drawback to Object offsets are 1) When the rotator is not at 0 deg obj, a declination offset is no longer vertical and RA offset no longer horizontal on your image. 2) You must divide by cosine of the declination to get an RA offset in arcseconds on the sky. With instrument plane offsets the amounts are always in arcseconds on the sky and X-offsets are always horizontal and Y-offsets are always vertical regardless of rotator angle.

The second method is a bit more tedious, but you can have the rotator track with the sky, while being approximately perpendicular to the horizon. You need to determine what object rotation angle corresponds to 90 degrees horizon. There are several ways to do this. One way is to issue a TCC AXIS STATUS command using the tester buttons of Remark, while tracking with rotator set to 0 degrees object. The AXISSTAT word for AXIS 3 (which shows up in the debug window), gives the mount position of the rotator in degrees. Next move the rotator to 90 deg horizon, and repeat the TCC AXIS STATUS. The difference between the two is the object rotation angle you will need to put in to orient the slit perpendicular to the horizon, and still track the sky. Check this by issuing another TCC AXIS STATUS, once you have entered the object rotation angle to be sure you have the sign right.

AN EXAMPLE:

After you slewed to your object (rotator at 0 deg object), the rotator was at 122 degrees mount. After rotating to 90 Horizon, the rotator was at 29.5 mount. To orient the slit perpendicular to the horizon and track the sky, set the rotator to 122 - 29.5 = 92.5 degrees object. Now the rotator should read around 29.5 degrees mount. Now that you have the slit aligned roughly perpendicular to the horizon you can use instrument plane offsets to put the object on the slit in the same way described above when rotating with the sky (you can also use object offsets but determining which way is "up" is more tricky). Your object is at 420,442 on the red chip. So your offset will be (434 - 442)*0.610 = -4.9 " in Y in the instrument plane. You now have your object on the slit and the slit is roughly perpendicular to the horizon.

Items that need to be inserted into these pages but the links may not yet work

• default gratings setup
• detector characteristics
• operations manual
• remark interface
• lamp spectra
• blaze angles
• slit images
• command reference
• DIS III Characterization
• older information

Items that need to be inserted into these pages but the links may not yet work

DIS Detector Characteristics

DIS Operations Manual By Robert Lupton

Remark Interface and DIS(slightly out of date)

Some Slitview information that may be helpful when using DIS

If you are looking for information which relates to the slitviewer please see DIS Slit information

Setting Slit orientation

DIS Quick Start Guide (PDF)

Take Lamp Spectra (this can be done at the end of the night as well)

Focus DIS, using Slitviewer

Slew to your object

Find object in slitviewer

Center object in slit, on slitviewer using C(centroid) or I(for faint or extended objects, to use integer pixel position, ie. where the cursor is)

Set image name, sequence number, which cameras (Red/Blue or both) and comments.

You may also want to select to automatically send the image (FTP or display) to your computer.

Set exposure time and check that your configuration is what you want.

If the exposure is going to be longer than 180s, or you are going to be taking several exposures of the same object, ask the observing specialist to start the guider

Start your exposure