Finder and DIMMWIT Quickstart  Guide

• Finder, the acquisition system embedded in the COAST telescopes.
• DIMMWIT, the Differential Image Motion Monitor Which Is Transportable.

Using the window manager menu
From an Xterm

Connections and powering up
From an Xterm

The essential controls
Online help
Telescope status indicators

Initial Tasks
Alignment
Acquiring a Star

Acquisition
Recording r0 Data
Recording t0 Data

If You Plan to Use 1D DIMM Mode
If You Plan to Use 2D DIMM Mode
If You Plan to Use Transverse DIMM Mode
In Any DIMM mode

Starting Finder

Using the window manager menu

• Hold the left mouse button down while on the display background to invoke the menu.
• Move the mouse to the "Finders" submenu.
• Select the telescope you want to launch a finder for, or "All Finders" if you want to run them all.
• Let go the left mouse button.

From an Xterm

Starting DIMMWIT

Connections and powering up

• Connect the camera head to the USB interface using the custom cable.
• Connect the USB cable between the interface and the single board computer in its blue box.
• Connect the power cable already attached to the USB interface to the power transformer.
• Connect the 30m ethernet cable between the single board computer and your laptop computer (you can use a shorter cable if you like provided it is a Cat5 crossover cable).

• Boot your laptop first, so that DIMMWIT can see the connection when it is turned on.
  
• Switch on the single board computer (the voltage supply is autoranging but make sure the fuse is right for the mains voltage in your country).
• Wait 30 seconds for it to boot and initialise the USB interface.
• Plug in the power for the transformer.
  

From an Xterm

• To use the program stored internally in DIMMWIT, from an xterm type

ssh coast@dimmwit finder

• Enter the password when requested (NOTE: If you are using an older version of ssh it can take half a minute for the password prompt to appear. I don't know why!)
• The program will be displayed after a few seconds.
• To use the version on your host PC instead, type ssh coast@dimmwit remotefinder

Quick Tour

The essential controls:

Online help

• Tooltips. If the mouse cursor is held steady over a control a tooltip will pop up with a brief description of that control.
• Context sensitive help. Many controls have longer built in descriptions. These are accessed by clicking on the " " icon and then the control of interest.
• Status messages. When a menu item is highlighted, a brief description of its functionality appears in the status bar (unless you have turned off the status bar).
  

Telescope status indicators

• These become active when a finder is communicating with a COAST telescope.
• They indicate the status of the telescope secondary mirror and beamsplitter.
• They are arranged to look like a ray-trace of the light through the telescope.
  
• They cannot be used to move telescope optics.
• Their appearance is as follows:
  

Status	Secondary	Beamsplitter
Out
Moving
In

Acquisition at COAST (Finder)

Initial Tasks

• Start the telescope user interface using the "start" script on apcsttel.

• Click on the " " to get finder talking to the telescope controller.
• Click on the " " to get it talking to the CCD.
• If all is well, the "disconnect" equivalents of these icons will become available.
• If the camera head does not have power (if the beamsplitter is out) the video display will stay dark.
  

Alignment

• Use the telescope controller to put a beamsplitter in for the telescope of interest.
• Send the artificial star beam out to the telescope flat.
• Manually align the telescope piezo as usual using the telescope controller and the finder display.
• Check that the crosshair on the finder display is centred on the star image. The crosshair marks the spot we will want to guide stars to later (it's like the crosshairs of the old finder).

• Click on the " " located in the toolbar.
• Move the cursor into the video display area. Its shape will change.
• Click on the centre of the star image.
• The crosshair moves to the new location and the cursor changes back to its default shape.
• Do this for all the telescopes you want to use.

Acquiring a Star

• Use the telescope controller to point a telescope at the star of interest and make sure the secondary is out.
• You will hopefully see the star you want to acquire. Select...

 

...if the display is faint. This linearly maps the dynamic range of the image to the entire display range of the monitor.

• Click on the " " located in the toolbar.
• Move the cursor into the video display area. It will change shape into a region selection cursor.
• Drag a rectangle across the star you want to acquire.
• If you are not satisfied with your selection repeat the above. Otherwise, start tracking by clicking on the " " located in the toolbar. Finder will start to subframe your selected region of interest and offsets for the telescope controller will appear in the LCD panels and in the telescope controller display.
• Tell the telescope controller to use the finder acquisition offsets.
• The telescope will guide the star image to the crosshairs.
• If something goes wrong, click on " " to stop tracking, and/or " " to stop tracking and revert to full screen display.
  

• Click on the " " to stop tracking.
• Tell the telescope controller to put the secondary in. Finder will revert to full screen display. Note: it will also stop tracking if you forgot to tell it to.
• You will hopefully see the star you want. Select it and guide it in as before.
• The star should now be on the autoguider display. Tell the telescope controller to use the guider offsets.
• Click on the " " to stop tracking.
• Tell the telescope controller to move the beamsplitter out. Note: finder will stop tracking and revert to full screen display if you forgot to tell it to.

Seeing Measurements (Finder and DIMMWIT)

• A mask with two or more holes is placed in the pupil plane of the telescope.
• Telescope optics are slightly defocussed so separate star images appear on the CCD.
• The differential image motion between the images is measured.
  

Acquisition

• If you are using a COAST telescope:
• The mask is a lens cap (with holes) placed on front of the CCD lens.
• We set the lens focal length to 210mm (full extension) and defocus slightly (set it to number "7" on the zoom ring).
• Acquire as above - but note that the star image is much fainter and there are several of them! So you may have to  do some manual guiding when you are close to the right position.
• Leave the telescope beam splitter in so you can autoguide and take seeing data at the same time.
  
• If you are working with a DIMMWIT:
• Your optical and acquisition arrangements will depend on the telescope you are using but in general:
• You need some kind of autoguiding mechanism to ensure the star images don't move much.
• Press the " " to get DIMMWIT talking to the CCD. It will start to read out immediately.
• In either case:
  
• You will hopefully see the star you want to acquire. Select...

 

...if the display is faint. This linearly maps the dynamic range of the image to the entire display range of the monitor. You can also look at the flux bar...

...to determine how appropriate your exposure settings are.

Recording r₀ Data

• Click on the " " located in the toolbar. This opens the Data File Parameters dialog.
• If you are using a COAST telescope, the default directory settings are fine. If you are using a DIMMWIT, choose a directory on your laptop hard disc for file saving.
  
• The other fields depend on your science goals. General guidelines (partly courtesy Bridget O'Donovan):
• Call the file "r0.fits". You do not have to invent new file names for each file you save, the software will insert a unique date and time in each filename.
• In the "On trigger acquire" fields choose 1 file of 900 images if you want to observe many targets in one night, otherwise choose 1 file of 6000 images (about 20 minutes observing time).
• Fill out the other fields, most importantly the "Object" field with the star being observed. These will be inserted as comments into the FITS file.
• When you are happy, click "OK".
• Click on the " " located in the toolbar.
• Move the cursor into the video display area. It will change shape into a region selection cursor.
• Drag a green rectangle across the star pair you want to acquire. This takes practice:
• The smaller the box is, the faster the readout rate. This is good.
• If the box is too small, one or both of the star images might drift out of the box during acquisition. This is bad.
• The following picture illustrates a typical suitable box size.
• [holding place for image]
  
• If you are not satisfied with your selection just click on the " " and start over.
• Click on the " " in the toolbar to initiate subframing.
• More general guidelines:
• Choose exposure time of 1ms.
• Turn charge clearing on.
• Choose 2x2 binning.
• Click on the " " located in the toolbar to start saving data.
• The "Data Saved" progress bar...

...will monitor the progress so far.

• The program will beep when the file has finished saving.
• To save another file with the same parameters as the first, all you have to do now is press " " again.
  

Recording t₀ Data

• 1D DIMM mode, which bins a 64x64 pixel subframe into a single 64 pixel line every 2ms.
• 2D DIMM mode, which bins a 64x32 pixel subframe into a 16x8 pixel array every 3ms.
• Transverse DIMM mode, which bins a 64x32 pixel  subframe into an 8x16  pixel array  every 4ms.
  

• More information on these modes is located in the user manual.

If You Plan to Use 1D DIMM Mode:

• Select...

• This draws a red grid on the display as shown below:

• Ensure that your star images appear in the same grid region, that is, there are no red lines between them.
• Important: ensure that you are doing full frame readout (press " " to set this) and binning is 4x4. Otherwise finder will crash for some unknown reason when you change modes!
• Click on the " " located in the toolbar to initiate 1D DIMM mode.
• A 1D line of charge will be displayed.

If You Plan to Use 2D DIMM Mode:

• Select...

• This draws a blue grid on the display as shown below:

• Ensure that your star images appear in the same grid region, that is, there are no blue lines between them.
• Important: ensure that you are doing full frame readout (press " " to set this) and binning is 4x4. Otherwise finder will crash for some unknown reason when you change modes!
• Click on the " " located in the toolbar to initiate 2D DIMM mode.
• A 2D array of charge will be displayed.

If You Plan to Use Transverse DIMM Mode:

• Select...

• This draws a yellow grid on the display as shown below:

• Ensure that your star images appear in the same grid region, that is, there are no yellow lines between them.
• Important: ensure that you are doing full frame readout (press " " to set this) and binning is 4x4. Otherwise finder will crash for some unknown reason when you change modes!
• Click on the " " located in the toolbar to initiate transverse DIMM mode.
• A 2D array of charge will be displayed.

In Any DIMM Mode:

• Click on the " " located in the toolbar. This opens the Data File Parameters dialog.
• If you are using a COAST telescope, the default directory settings are fine. If you are using a DIMMWIT, choose a directory on your laptop hard disc for file saving.
  
• The other fields depend on your science goals. General guidelines (partly courtesy Bridget O'Donovan):
• Call the file "t0.fits". You do not have to invent new file names for each file you save, the software will insert a unique date and time in each filename.
• In the "On trigger acquire" choose 1 file of 130000 images (65000 if you want to observe many targets in one night) for 1D DIMM measurements or 65000 images for 2D DIMM measurements.
• Fill out the other fields, most importantly the "Object" field with the star being observed. These will be inserted as comments into the FITS file.
• When you are happy, click "OK".
• Click on the " " located in the toolbar to start saving data.
• The display will freeze during acquisition. Even the "Data Saved" progress bar will not update.
  
• The above settings equate to about 4 minutes in 1D DIMM mode or 3 minutes in 2D DIMM mode.
• Important: Do not move the mouse or interact with the program in any way while saving t₀ data. This can cause dropouts in the data files which will ruin any later frequency analysis.
  
• The program will beep when the file has finished saving.
• To save another file with the same parameters as the first, all you have to do now is press " " again.
• To revert to normal 2D readout (to reacquire or to change targets) select the full frame readout button (" ").
  

Quitting Finder

• If connected to a COAST telescope, click on the " " to disconnect.
• Click on the " " to disconnect from the CCD.
• Select "Exit" from the "File" menu.
• If the configuration has changed (new crosshair position) finder will inform you before exiting.
• If you are using a DIMMWIT:
• (optional but preferred) From your xterm, type "ssh root@dimmwit poweroff" and enter the root password when requested to initiate a graceful shutdown.
• Switch everything off and disconnect in no particular order.