By Heidi Schweiker
Edited By Hillary Mathis


Latest updates
PDF version of the February 2011 manual (2.5Mb)

Telescope Operations

   Location of the 0.9m Telescope
   Safety Walk-through
   Safety Interlocks
   Filling the Dewar
   The Dome Cameras
   The Exhaust Fan
   The Wind Screen
   The Dry Air System
   Dome Vent Operation
   Startup Checklist
   Shutdown Checklist
   Overview of the TCS
   Starting Up the TCS
   Telescope Park Positions
   Importing Coordinate Catalogs
   Aquiring an Object
   Small Telescope Motions
   Moving the Dome
   TCS/Instrument Communication
   Checking the Weather
   Data Acquisition Computers
   Checking and Zeroing Pointing
   Changing Filters with S2KB
   Dome Flats
   Guiding with Mosaic
   Guiding with S2KB
   Automated CCD Log
   S2KB Information
   WIYN 0.9m/S2KB FAQs
   The MOSAIC Manual

Troubleshooting Tips
Startup Checklist
Shutdown Checklist
End of Run Checklist


   Lightning Shutdown Procedures
   Extended Horizon Map
   Additional S2KB Information
   The KPFILT script
   More on the Mosaic Guider
   A Unix Cheatsheet
   An IRAF Cheatsheet
   An SFTP Cheatsheet
   An EMACS CheatSheet
   An Vi CheatSheet
   A Guide to Taking Sky Flats
   Dewar Filling Tips and Tricks
   Taking a Seeing Measurement

Other Useful References

   0.9m User's Manual
   ICE Observing Manual
   Direct Imaging Manual
   The MOSAIC Manual




KPNO Telescope, Filter, and Detector Database

# KPNO Telescope, Filter, and Detector Database
# Revised on the basis of drawings (true aperture size) and
# improved count rates. Agrees with KPNO Direct Imaging Manual
# 1 May 1997 --- plm
# 22 Jul 1998 --- dj
# 12 Aug 1998 --- gj

# Telescope data:
# aperture diameter in meters, scale in arcsec/mm, and transmission.

  • telescope = "0.9m"
    • aperture = 0.81
    • scale = 28.3
    • transmission = 1.0
  • telescope = "0.9mf13"
    • aperture = 0.81
    • scale = 15.9
    • transmission = 1.0
  • telescope = "4m"
    • aperture = 3.42
    • scale = 17.5
    • transmission = 1.0
  • telescope = "4mf8"
    • aperture = 3.42
    • scale = 6.67
    • transmission = 1.0
  • telescope = "4mf15"
    • aperture = 3.42
    • scale = 3.75
    • transmission = 1.0
  • telescope = "2.1m"
    • aperture = 1.94
    • scale = 12.7
    • transmission = 1.0
  • telescope = "2.1mf15"
    • aperture = 1.94
    • scale = 6.5
    • transmission = 1.0
  • telescope = "Schmidt"
    • aperture = 0.61
    • scale = 96.4
    • transmission = 0.7
  • telescope = "WIYN"
    • aperture = 3.185
    • scale = 9.4
    • transmission = 1.0
  • end

# Filter data:
# Magnitude corresponding to photon count rate.
# Photons/second/stellar-image for a 1-m telescope at 1 airmass.
# Sky magnitudes per sq arc sec:
# sky = sky0 + sky1 * phase + sky2 * phase**2 (phase=0-14)

  • filter = "U"
    • extinction = 0.55
    • mag = 20
    • star = 8.0
    • sky0 = 22.0
    • sky1 = -0.2666
    • sky2 = -.00760
  • filter = "B"
    • extinction = 0.25
    • mag = 20
    • star = 34.5
    • sky0 = 22.7
    • sky1 = -0.0998
    • sky2 = -0.00953
  • filter = "V"
    • extinction = 0.14
    • mag = 20
    • star = 36.2
    • sky0 = 21.8
    • sky1 = -0.0153
    • sky2 = -0.00838
  • filter = "R"
    • extinction = 0.10
    • mag = 20
    • star = 36.8
    • sky0 = 20.9
    • sky1 = -0.0211
    • sky2 = -0.00364
  • filter = "I"
    • extinction = 0.05
    • mag = 20
    • star = 26.7
    • sky0 = 19.9
    • sky1 = -0.0086
    • sky2 = -0.00311
  • filter = "J"
    • extinction = 0.08
    • mag = 20
    • star = 36.5
    • sky0 = 16.2
    • sky1 = 0.
    • sky2 = 0.
  • filter = "H"
    • extinction = 0.04
    • mag = 20
    • star = 21.8
    • sky0 = 14.2
    • sky1 = 0.
    • sky2 = 0.
  • filter = "K"
    • extinction = 0.07
    • mag = 20
    • star = 14.6
    • sky0 = 13.3
    • sky1 = 0.
    • sky2 = 0.
  • end

# Detector information:
# rdnoise in photons, dark rate in photons per second, pixel size in microns,
# and the effective DQE for each filter.

  • detector = "MOSAIC1"
    • rdnoise = 5.0
    • dark = 0.0015
    • pixsize = 15
    • U = 0.48
    • B = 0.68
    • V = 0.81
    • R = 0.86
    • I = 0.63
  • detector = "T1KA"
    • rdnoise = 3.5
    • dark = 0.001
    • pixsize = 24
    • U = 0.24
    • B = 0.44
    • V = 0.70
    • R = 0.79
    • I = 0.59
  • detector = "T2KA"
    • rdnoise = 4.0
    • dark = 0.001
    • pixsize = 24
    • U = 0.31
    • B = 0.53
    • V = 0.63
    • R = 0.67
    • I = 0.51
  • detector = "T2KB"
    • rdnoise = 4.0
    • dark = 0.001
    • pixsize = 24
    • U = 0.42
    • B = 0.67
    • V = 0.78
    • R = 0.79
    • I = 0.56
  • detector = "TI5"
    • rdnoise = 8.6
    • dark = 0.001
    • pixsize = 15
    • U = 0.51
    • B = 0.59
    • V = 0.69
    • R = 0.61
    • I = 0.39
  • detector = "T5HA"
    • rdnoise = 13.5
    • dark = 0.001
    • pixsize = 27
    • U = 0.30
    • B = 0.51
    • V = 0.64
    • R = 0.69
    • I = 0.50
  • detector = "S2KA"
    • rdnoise = 3.0
    • dark = 0.001
    • pixsize = 21
    • U = 0.30
    • B = 0.18
    • V = 0.34
    • R = 0.40
    • I = 0.60
  • detector = "S2KB"
    • rdnoise = 7.0
    • dark = 0.001
    • pixsize = 21
    • U = 0.40
    • B = 0.70
    • V = 0.80
    • R = 0.82
    • I = 0.60
  • detector = "IRIM"
    • rdnoise = 35
    • dark = 1
    • pixsize = 167
    • J = 0.23
    • H = 0.33
    • K = 0.31
    • K' = 0.38
  • detector = "ONIS"
    • rdnoise = 35
    • dark = 0.75
    • pixsize = 27
    • J = 0.18
    • H = 0.28
    • K = 0.22
    • K' = 0.34

Normal Bias Image

Bad Bias Images


The kpfilt script


Observers can insert the filter names into their image headers by running the included script after they have taken their images. The steps to run it are as follows:

  • Determine which filters are in each wheel. For example:
    Filter Wheel 1:
    0 Empty
    1 U
    2 B
    3 V
    4 R
    5 I
    Filter Wheel 2:
    0 Empty
    1 SII
    2 H alpha
    3 O III
    4+ Empty
  • The locations of the two filters bolts are stored in the header as two numbers separated by a zero. The keyword FILTERS is used to indicate this. So that FILTERS = 100 means that filter 1 is in position 1 and filter 2 is in position 0.
  • The kpfilt script uses the FILTERS keyword to determine which filter name should be placed in the header. The statements look like this....
      if (filt==" 100"){
    # hedit imgname FILTER U ver- show+ add+
         hedit (imgname, fields="FILTER", value="U", add=yes, delete=no,
                       verify=no, update=yes)
    The user needs to change the value of 'filt' that corresponds to the U filter or alternatively exchange the name of the filter that sits in the '100' slot.
  • Tell IRAF where the script lives using
    task = /path/
  • Then, just type kpfilt image or kpfilt @list_of_images.

The kpfilt Script

# This will name the filters to things that make sense
# Brian Marsteller, Michigan State University

procedure kpfilt (input)

string input {"",prompt="Input images"}

struct *inlist

string filt

string intmpfile

string imgname

# This will set things up in case your input is a list

intmpfile = mktemp ("intem")
files (input, sort=no, >> intmpfile)
inlist = intmpfile

while (fscan (inlist, imgname) !=EOF){

  imgets (imgname, param="FILTERS")
  filt = imgets.value

  if (filt==" 100"){
# hedit imgname FILTER U ver- show+ add+
     hedit (imgname, fields="FILTER", value="U", add=yes, delete=no, verify=no, update=yes)

  if (filt==" 200"){
# hedit imgname FILTER B ver- show+ add+
     hedit (imgname, fields="FILTER", value="B", add=yes, delete=no, verify=no, update=yes)

  if (filt==" 300"){
# hedit imgname FILTER V ver- show+ add+
     hedit (imgname, fields="FILTER", value="V", add=yes, delete=no, verify=no, update=yes)

  if (filt==" 400"){
# hedit imgname FILTER R ver- show+ add+
     hedit (imgname, fields="FILTER", value="R", add=yes, delete=no, verify=no, update=yes)

  if (filt==" 500"){
# hedit imgname FILTER I ver- show+ add+
     hedit (imgname, fields="FILTER", value="I", add=yes, delete=no, verify=no, update=yes)

  if (filt==" 001"){
# hedit imgname FILTER SII ver- show+ add+
     hedit (imgname, fields="FILTER", value="SII", add=yes, delete=no, verify=no, update=yes)

  if (filt==" 002"){
# hedit imgname FILTER Ha ver- show+ add+
     hedit (imgname, fields="FILTER", value="Ha", add=yes, delete=no, verify=no, update=yes)

  if (filt==" 003"){
# hedit imgname FILTER OIII ver- show+ add+
     hedit (imgname, fields="FILTER", value="OIII", add=yes, delete=no, verify=no, update=yes)






Guider Control GUI

Guider GUI

The Guider control graphical user interface is started from the 'Guider GUI' icon on the desktop.

Information fields

The information fields X, Total Count, FWHM, X Ref, Y, Max Value, Background, Y Ref, RMS X, and RMS Y contain status information which updates either when the guider is ON, or when it is calculate only mode.

X and Y

These values are the current guider box center positions in integer pixel coordinates.

Total Count

The total count is the number of counts summed over all pixels in the guider box. It provides a relative indicator of signal strength.


The FWHM is the full-width-half-max of the guider star image and can be used as a rough indication of guide signal quality. The value is in arcseconds.

Max Value

This is the maximum pixel value inside the guide box. As the digitization is 8-bit, the maximum possible value is 255, which represents signal saturation. If the signal is constantly above 240, then turn down the controller gain. Expect to see this number fluctuate; if it seems to be pegged you may be saturating even if the value is not 255.


The background is an estimate of the sky background. It is calculated using the pixels around the perimeter of the guide box. If the background is high (>50), then increasing the guide box size is recommended.

X Ref and Y Ref

The X and Y Ref values are the measured centroid deviations. These are in units of arcseconds and provide an indication of the amount of correction the guider is making. The actual corrections applied are somewhat smoothed (see Guide AV and Gain).


The RMS values show the root-mean-square values of the last "n" centroid measurements. The value of n is shown. To reset n to zero, select a guiding mode using the "Mode" menu. The default mode is "Intensity Centroid".

Interactive Fields

The interactive fields Leaky AV, Guide AV, Box Size, Increment, Gain, VContrast and VBright, are fields which can be changed by the arrow buttons to their right.

Leaky AV

This value is the amount of "Leak". The units are "number of frames". For example, selecting a value of 3 will use a running average of 3 frames. This helps to reduce background noise and bring out fainter objects. Values above about 5 are unlikely to be used except during acquisition of very faint targets.

Guide AV

The Guide AV value controls the number of guide star centroid measurements to average, BEFORE sending a guide correction to the TCS. This does not change the appearance of the video picture but it does change the frequency of pointing correction. The default value is 10; larger numbers may be useful to avoid over-correction if there is a lot of image motion. Values of less than 10 are NOT recommended as the TCS may have problems accepting corrections at this rate.

Box Size

This value controls the size of the guide box (in pixels). It needs to be an odd number of pixels, so it will only change by 2 pixels at a time up or down. The ideal size for the guide box will provide a few pixels of "sky" between the guide star and each box edge.


This value controls the step size (2, 10, or 100 pixels) by which the guide box can be moved around the screen. When the guider gui window is selected, the "arrow" cursor keys have the effect of moving the guide box inside the subraster box. To move both boxes together, hold down the "shift" key while pressing the arrow keys. Be sure not to hold down the arrow key - this is known to crash the program. Manual control of the guide box will not usually be needed because the box will "warp" to the guide star automatically in most circumstances.


The Gain parameter is an interactive value which controls how much of the guiding correction actually gets sent to the TCS (default 0.8). For example, a gain of 0.5 means that if the measured error is 1.0 arcseconds, then the guider would send a correction of only 0.5 arcseconds. Setting the Gain low and the Guide AV low can give excellent results in good seeing. The Gain will normally be set between 0.4 and 1.0 in normal operation. The "Guider" menu has an autotune option which attempts to determine the best settings for the "Gain" and "Guide AV" parameters for you. NOTE: autotune is only going to work when the seeing is good.

Log file name field

This entry field issued to alter the log file. Enter a new log file name (including the directory path) and press RETURN to activate it.

Status line

The bottom of the window contains the status fields, which are:

  • Guider status - on (green), off (flashing red), calculate only (flashing yellow)
  • Focus - f8
  • Sampling - panoramic (whole screen) or subraster (maximum speed)
  • Mode - type of centroid used (intensity, moment, shectman, quadrant, gaussian)
  • Box

Guide control (menu) options

The major operations are controlled via menu selections. The menus available are:


Guider menu

Display guider

Guider On

Switch guiding on.

Calculate Only

This mode of operation does all the calculations identically to normal guiding mode, but never sends any corrections to the TCS.

Guider Off

Switch guider off.

Guider Lock

Defines the precise position at which to guide. Normally, guiding occurs at the center of the guide box: selecting guider lock will make the guider attempt to keep the guide star at its CURRENT location (at the moment you select this option) within the guide box. The guider-lock status is independent of guider on/off, and may be used while guiding is on or off. If you select guider lock, then move the telescope and switch guiding on, it will guide back to the precise position when guider-lock was selected. The guider-lock position is zeroed by a "Warp to star" operation. See also Locks menu below.

Warp to star

Locates the brightest guide star in the field, and centers the guide box on it. This option may be used while guiding is on or off. Note that the guider cannot use stars too close to the edge, defined to be such that the subraster would overlap the full video field. The guide box will not move if the brightest star in the field is unavailable: you will need to move the guide box manually to another star in the field.

Calibrate guider

The guider has information about the instrument and telescope focus, and will automatically adopt the appropriate pixel scale. This option is not used at the 0.9m.

Autotune guider

This option automatically adjusts the guider parameters (Guide AV and Gain) through a set of possible values. At each setting the RMS behavior of the guiding offsets is calculated. The best combination of parameters is then presented to the operator for confirmation. This option will only be worthwhile in good to excellent seeing.

Measure background/Subtract background

These options are used together to improve the guider performance when the sky background is high or the guide star is faint (ie. in low contrast situations). It can also remove detector gradients or other camera pattern noise. First, move the guide star, and any other visible stars, out of the field and click "Measure background". After approximately 20 seconds the average background will have been measured. Click on the "Subtract background" option and the screen should go almost black. Now move back to your guide star.

The guider algorithm defines loss of signal depending on how much brighter the guide star is than the background. Background subtraction forces the background to almost zero, and thus lets you guide in extreme conditions.

Snap image

Save a FITS format copy of the full 640x480 video field to disk. Images are saved in files called frame_XXXXX.dat, where the running number is simply incremented on each save operation.

Save 512 subimages to disk

Save a sequence of 512 FITS format snaps of the 65x65 subraster of the video field to disk. Images are saved in files called sampleXXX_yyy.dat, where the running number XXX is incremented on each save operation, and the number yyy runs from 000 to 511.

Guide image quality monitor on/off

This option is used to gain a quick look at the instantaneous image quality of the guide star. It may be useful for fine focusing and determining if the seeing has suddenly changed (better or worse), or is stable or variable. This puts up a continuous sequence of subraster field across the video image (NOTE: this does not interfere with guiding and only changes the display). This option can be used when guiding is on or off.

Field scale options

These options allow you to select the appropriate telescope focal ration. There is only one focal ratio used at the 0.9m (f/8), which is automatically selected on startup so this should never need to be changed.


Quit the guider GUI. NOTE: this does not turn off guiding, it only shuts down the guider program. Guiding will continue until manually turned off.


Locks menu

Define lock position X

Set up any of four available lock positions at the current centroided star location.

Goto lock position X

Move the guider box to the lock position

Clear lock positions

Undefine all lock positions. Note that the guider still knows where they are and you can still move to them, but you will not be able to save them. This option was more important in earlier versions of the guider software.

Save/Load lock positions

Save or load the current lock positions to or from a disk file. A dialog box will prompt you for a filename.


Markers menu

A set of up to 4095 markers may be created and optionally saved and restored to and from disk files. The current marker is always indicated by extended vertical features. Once a new marker is created it automatically becomes the current marker.

To cycle through a set of markers use the ALT-+ key combination. The cursor must be in the GUI window for this and the following key combinations to work.

CAUTION: Please switch guiding OFF before cycling between markers.

To move the current marker (one pixel at a time) hold down the ALT key and press an arrow key.

To delete the current marker, hold down the ALT key and press the Del key.

Add marker at current box center

Adds a new marker at the center of the guide box.

Add marker at guider center

Adds a new marker at the center of the screen (i.e. x=320,y=240).

Clear markers

Delete all markers

Save/Load markers

Save or load the marker positions to or from a file. A dialog box will prompt you for a filename. These files are on the guider computer and are not generally accessible except from these menu options.


Mode menu

Panoramic Mode

This option selects full screen mode digitization. Depending upon available CPU this mode will run at approximately 8 frames per second.

Subraster Mode

This option selects Subraster mode digitization. A full video frame rate of 30Hz is possible with this mode. CAUTION: only the area inside the larger box on the screen in updated when in subraster mode. This is the default mode when guiding.

Intensity centroid

Selects a simple intensity centroid calculation. In practice this method seems to work as well as any, and is the most robust with noisy signals.

Moment centroid

Uses a very simple "moment" calculation. May be of some use in very poor signal conditions.

Shectman centroid

The classic Shectman centroiding algorithm.

Quadrant centroid

A simple quadrant centroid calculation. May be useful for very low signal conditions.

Gaussian centroid

A full gaussian parameter fit with centroid calculation. The extra processing is only worthwhile when a very good guide signal is available.

Guide/Subraster Box


Window menu


Diagnostics and engineering window which allows low level access to the guider functions. DO NOT USE THIS unless you are the responsible programmer!

History graphs

The history graphs window contains the following six historical data plots, which can be used to evaluate the efficacy of the guiding.

X correction: the guide correction in arcseconds in the X axis

Y correction: the guide correction in arcseconds in the Y axis

Total Count: the summed signal inside the guide box

FWHM: the full-width-half-max in arcseconds

X data: the guide star signal summed by column (ie an X slice)

Y data: the guide star signal summed by row (ie a Y slice)


The help menu contains only one item, "About TV Guider", and no useful help information.


Common UNIX commands
  • cp - CoPy an existing file to a new file.
    Format: cp <existing file> <new file>
  • df - Stands for Disk Free and shows the amount of disk space available on the currently mounted disks.
    Format: df -k
  • ftp - Stands for File Transfer Protocol. Allows you to transfer files back and forth between the 0.9m and your home institution.
    Format: ftp <host computer IP address>. Once you are connected you can use the get and put commands to manipulate files.
  • kill - KILL a currently running process.
    Format: kill -9 <PID>, where PID is the process identification obtained from the ps command.
  • lpr - PRint a file on the Laserprinter.
    Format: lpr <file name>
  • ls - LiSt the files in the current directory.
    Format: ls
  • mail - Allows you to check your email. You can also use Pine, which is a keystroke driven mail program. Pine is recommended over mail
  • man - Invokes the UNIX MANual pages allowing you to get help on any UNIX command.
    Format: man <Unix command>
  • mkdir - MaKe a new DIRectory.
    Format: mkdir <directory name>
  • mv - MoVe an existing file to a new file, which is the same as renaming the original file.
    Format: mv <existing file> <new file>
  • ps - Displays the currently running ProceSses.
    Format: ps -x
  • rm - Delete (ReMove) a file.
    Format: rm <file name>
  • sftp - Secure FTP.
  • ssh2 - Stands for Secure SHell. Allows you to log into another computer using a secure connection which protects the privacy of information passed between the two computers.
    Format: ssh2 <host computer IP address>.
  • tar - Stands for Tape ARchive. Allows you to make a backup of your data onto a magnetic tape.
    Format: tar cvf <tape device name> <files to be backed up>

Useful web page:


Common IRAF commands
  • ccdinfo - Outputs basic information about the CCD including the available gain settings.
  • detpars - Set the gain value, region of the chip to readout, etc.
  • display - Displays an image in the ximtool window.
  • flpr - Stands for 'flush process'. It is recommended that flpr be issued anytime ctrl-c is used to interrupt a process.
  • imexamine - allows the user to use certain keystrokes to operate on the currently displayed image in the ximtool window. Useful keystrokes include r (plots a radial profile and outputs profile diagnostics), a (only gives the profile diagnostics), c (plots a contour plot), and s (plots a surface plot).
  • imhistogram - Plots a histogram of the pixel intensity values. Note that the ordinate is a logarithmic scale. This is useful for checking the distribution of pixel values looking for a stuck bit, which would manifest itself as a sequence of intensities with no pixels.
  • implot - Plots pixel intensities along row and columns.
  • observe - The primary observing command, which initiates and otherwise controls CCD exposures.
  • obspars - Set the run information, nightly file prefix, up date the current image index number, etc.
  • rfits - Read a fits file or convert a FITS image to an imh/pixel image.
  • test - Takes one exposure and saves it to test.imh without incrementing the image index.
  • unlearn - Resets IRAF parameter sets to their default values.
  • wfits - Write a FITS file or convert an imh/pixel image to a FITS image.

Useful web page:


Why use sftp instead of ftp?

  • sftp is a more secure way to transfer files, as compared to ftp. Many sites that hide behind firewalls and no longer support ftp will support sftp.

How does one use sftp? Using sftp is similar to, but not identical to using ftp. Here is a sample session:

  • > sftp
  • Connecting to
  •'s password:
  • sftp> put test*
  • Uploading test.1 to /data1/36inch/test.1
  • Uploading test.2 to /data1/36inch/test.2
  • Uploading test.3 to /data1/36inch/test.3
  • Uploading test.4 to /data1/36inch/test.4
  • sftp> quit

Comments: "36inch" is the userid, and "" is the address. After the password is typed in correctly, you get the "sftp>" prompt. A simple "put" (not "mput") will transfer all the files indicated by the wildcard character; in this case, the four test files shown. Additional info can be found from "man sftp", e.g. on taupe.


Common Emacs keystrokes
  • Ctrl-x Ctrl-s - Save changes to the current file.
  • Ctrl-x Ctrl-c - Quit emacs.
  • Ctrl-b - Back one space.
  • Ctrl-f - Forward one space.
  • Ctrl-k - Delete entire line.
  • Ctrl-x u - Undo last change.
  • Alt-v - Previous page.
  • Ctrl-v - Next page.

Useful web page:


  • x - Delete a single character. 2x deletes two characters.
  • j - Move the cursor down one row.
  • h - Move the cursor left one space.
  • k - Move the cursor up one row.
  • l - Move the cursor right one space.
  • :w - Save changes to the current file.
  • :wq - (Write and Quit) Save changes to the file and quit vi.
  • :q! - Quit vi without saving changes.
  • i - Insert.
  • u - Undo last change.
  • D - Delete from character to end of line.
  • dw - Delete word.
  • Ctrl-b - Previous page.
  • Ctrl-f - Next page.

Useful web page: http:/ /


The following describes a method that provides useful twilight sky flats at the 0.9m telescope using either the MOSAIC or S2KB setups.

Philosophy: If you want to use twilight sky flats (instead of dome flats) to correct for pixel-to-pixel sensitivity variations, then you need at least 5 well-exposed sky flats in each filter each night. If you want to use twilight sky flats in conjunction with dome flats to do an illumination correction (twilight flats will be smoothed), then you need at least 3 flats per filter approximately every other night.

The following describes how to obtain 5 twilight sky flats in each filter. The aim is to expose the CCD to between 1/3 and 2/3 of the full well. If the level is not optimum, adjust the exposure times appropriately.

  • Begin a few minutes after sunset.
  • Point the telescope at Dec ~ +30 and HA ~ -4h (east) and make sure tracking is ON.
  • Take a very short exposure (~1 sec) using the filter where the system throughput is lowest (e.g. U). This image is likely to be saturated.
  • Keep taking short exposures with the same exposure time until the CCD is exposed to about 2/3 of its full well.
  • Move the telescope a few degrees west (following the setting sun).
  • Take an exposure with twice the exposure time as the previous one.
  • Repeat steps 5 and 6 for the next 4 exposures adjusting the exposure time appropriately.
  • Move the telescope about 10 to 20 degrees west.
  • Change filters to the one with the next highest throughput (e.g. B).
  • Take an image with the same exposure time as the last image in the previous filter.
  • Move the telescope a few degrees west.
  • Take an exposure with twice the exposure time as the previous one.
  • Repeat steps 8 through 12 for the next 4 exposures.
  • Continue until the sky gets too faint to provide enough illumination to give you a mean level of about 1/3 of the full well in a 5 minute exposure.
  • About 15 to 20 minutes (exact time varies considerably based on your specific circumstances) into astronomical twilight, begin the process of taking morning twilight flats.
  • Point the telescope at Dec ~ +30 and HA ~ -4h (east).
  • Perform the above steps in reverse order making sure to begin with the longest exposure time and progress to the shortest times and moving the telescope west again to move away from the rising sun.


Filling a dewar can be tricky, but once you've figured out the right techinque it will become second nature. Below are a few pointers to help you make sure the dewar has gotten a good fill.

  • You must have the telescope parked at the Zenith Park position in order to fill the dewar.
  • The fill line must be precooled. When precooling the liquid nitrogen line, lay the line on the ground pointed away from all persons nearby.
  • When the line is precooled turn off the LN2. Attach the (precooled) liquid nitrogen line to the dewar. Lightly tighten the hose to the filling elbow.
  • Many people have trouble determining when the dewar is actually full. This is especially tricky to determine when the liquid nitrogren line is not properly seated on the dewar, causing nitrogen to leak around the connection. The dewar is full when you see a stream of liquid spraying out of the 3 small holes above this connection (looks like a sprinkler).
  • To remove the liquid nitrogen line from the dewar elbow use the wrench. The hose should easily loosen and the wrench should only need to be used for about half a turn, it should be finger tight by then. If the hose will not easily loosen you will need to use the heat gun to thaw out the area. When using the heat gun, you do not want the heat gun touching any of the surrounding metal - this could send vibrations up into the dewar. Keep the heat gun approximately 2 inches away from the dewar/line. Also keep the heat gun pointed away from the yellow plastic connector just beside the connection.
  • Do not touch the aluminum end of the heat gun after use - THIS IS VERY HOT! After use, be sure to rest the heat gun on the counter with the nozzle pointed up to make sure it doesn't come in contact with anything.
  • When removing the liquid nitrogen line from the dewar,after using the heat gun, unscrew the line as quickly as possible to avoid refreezing of the line onto the dewar threads. This is especially true in high humidity conditions. If the line does refreeze onto the threads, DO NOT USE FORCE TO REMOVE THE LINE. Reheat the area with the heat gun.
  • If your dewar has warmed up, see the Troubleshooting section Dewar Warmups.


We are seeking to track the seeing quality of the 0.9m telescope. As such, we would like each observer to measure the seeing toward the end of the night using the following procedure.

  • We need an uncrowded star field with airmass less than 2, preferably less than 1.5. A standard star field or one that you are currently observing are fine as long they fulfill these criteria.
  • At the end of the night before morning twilight begins, take a short (2 to 5 seconds) unguided exposure of the star field with the V filter.
  • Use IMEXAMINE in IRAF to measure the FWHM for 3 well-exposed (peak counts between 5,000 and 20,000 ADU) stars in the image and report the average value in the nightlog.

*Note that having the dome vents open and the telescope exhaust fan on (weather permitting) helps to improve the seeing.

Last updated February 3, 2008