BGSU 0.5-m Telescope + CCD Camera for ASTR 309

Procedure Outline

Starting Up:

1) The CCD PC in the control room should be shutdown when you arrive. Check that it is shutdown by looking at the light by the power button on the PC tower, and by typing on the keyboard -- nothing should happen. If it is on, shut it down. If/when it is shut down, you can go to the dome and plug the CCD cable into the CCD (be gentle, hand-tighten the screws on the connector).

WARNING: Never plug in or unplug the cable to the CCD when the PC is powered up -- you will damage or destroy the CCD!

If you will use the filter wheel, plug the small connector bound with the CCD cable into the filter wheel unit. Then get the power transformer (usually on a tall back shelf in the control room), plug it into the 110V power near the reticle light control knobs, and the small end into the filter wheel unit.

Start up the PC by pushing the power button on the front of the PC tower and wait for the PC to boot up.

2) Start the MaxIm_DL CCD program by double-clicking on the "Shortcut to MaxIm_DL" icon.

3) Initialize the CCD camera and (optional) the filterwheel.

4) (Optional) Set the camera temperature to keep the CCD cooled to a constant temp -- it may take a few minutes to stabilize, you can do Steps 5-7 while it cools.

5) Open the telescope as usual, following the procedure sheet kept in the control room.

6) Zeropoint the telescope coordinates on a bright star as usual using the visual eyepiece.

7) In the dome, slide the visual eyepiece all the way to the right and tighten the thumbscrew (so it doesn't obscure the CCD!). Set the telescope focus to the default CCD value (2382 units).

8) (Optional--Advanced) At twilight, if there are no/few clouds outside, take twilight sky flats.

9) Focus the telescope, and re-zeropoint the telescope for the CCD.


10) Start a paper log of your observing. Pages are available on top of the PC tower. Be sure to document the sky conditions, moon phase, etc when you begin.

11) In the "MaxIm CCD" window, select the Settings tab. In the "Auto Calibration" field, click the Simple Auto-dark radio button. [Why?]

12) Point the telescope to the coordinates of your target object and observe the object. Note the observation (especially the file name of the image!) in your paper log.

13) Repeat Step 12 until you are done, it is dawn, or it clouds up. Refocus (Step 9) if the stars start looking blurry.

Shutting Down:

14) If using the filter wheel, set it to the 5=I-filter position and take a 1 sec exposure to ensure it turns to that position.

15) If you cooled the CCD, warm it to dome temperature -- you can do Steps 16-17 while it warms.

16) Close up the telescope as usual following the procedure sheet kept in the control room.

17) Slide the visual eyepiece back to the center position (7.5 on the scale) and set the focus to the default visual focus value (2420).

18) When the CCD temperature has stabilized, re-select the Setup tab in the "MaxIm CCD" window, return the filterwheel to "No Filter = Filter", and click the Shutdown button.

19) Quit the MaxIM_DL program and shut down the CCD PC computer.

20) Record your observing session in the telescope log in the dome.

Note: if you have trouble:

Here are some links that you may find useful:

Updated 2002 Nov 12 -- ACL

Link to the Camera and Filter Wheel

Note: In order to send and receive information from the camera, or to make the filter wheel turn, there must be links established to these devices.

1) If it did not appear already, bring up the CCD control window "MaxIm CCD" by clicking on the button icon on the toolbar (8th from the left).

2) The three boxes along the left of the window should read:

If these do not appear, choose them correctly from the drag-down menus (see Troubleshooting).

3) When all is correct, click Restart to initialize the camera and filter wheel.

Updated 2002 Nov 12 -- ACL

Setting the CCD Temperature

Note: In general, CCD's perform best, producing the lowest noise, when they are cooled well below freezing (0 C). We also want to keep the CCD at a constant temperature all night, so its noise and sensitivity characteristics stay constant.

Our CCD camera has an automatic temperature control which makes it pretty easy to set and forget, but it is important to set it correctly at the beginning of the night. The camera assembly contains a thermoelectric cooler that can drive the CCD temperature down to about 30 C below the ambient air temperature in the dome. We will try to keep the CCD at -10 C, though if the dome temperature is 20 C or above, we won't get that low.

1) Select the Setup tab in the "MaxIm CCD" window, and click the Cooler On box. Enter "-10" into the box labeled New (C) and click the Set button.

2) The message "Cooling Down" should appear in the box at the bottom of the window, and the temperature in the Actual box should change in the direction of Setpoint. It may take a few minutes for Actual and Setpoint to match. Don't take any pictures until they match -- you can continue starting up the telescope while the CCD cools.

Note: only rarely will the values in Actual and Setpoint match exactly -- usually Actual shifts around within 1-2C of the Setpoint value -- this is normal.

4) At the end of the night, you should allow the CCD to warm up to dome temperature before turning off the CCD. Do this by selecting the Setup tab in the "MaxIm CCD" window, and clicking the Go to Ambient box. You will see the Actual value change away from Setpoint, and the message in the box will say "Cooler Regulating". It may take a few minutes to warm up, so be patient. You can continue shutting down the telescope while the CCD warms.

Updated 2002 Nov 12 -- ACL

Focusing the Telescope with CCDSoft

General: We will determine the best telescope focus by obtaining a series of short exposures of a bright star, stepping the focus slightly from one exposure to the next. MaxIm has a handy tool which allows us to determine which focus setting gives the best focus (that is, the narrowest images with the highest peak intensity). We then set the telescope focus to that value. You can read more about this procedure in the MaxIm CCD Manual (pp.4-3 to 4-5).

1) Pick a Focus Star near the meridian from the list of candidates taped to the side of the PC CCD tower. Point the telescope to this star.

2) Set a starting focus -- generally, we start 5 units below the default focus (2382-5=2377). Using the buttons on the handpaddle, drive the focus 10-15 units below this value, then approach the starting value from below. There may be some "backlash" in the focus screws, so always approach focus from below.

3) Using a piece of scrap paper, scrawl a "focus table" on it. For each focus image you take, record:

5) Select the Focus tab on the "MaxIm CCD" window, and

this will take one 12 sec exposure and write it to the screen, then pause.

6) Find your focus star on the image (see Focus Star Finder Charts in blue binder if needed).

7) Select the Inspect tab on the "MaxIm CCD" window. You see a 3-D picture of what the star's shape looks like, along with measurements of the FWHM in X and Y (the width of the star image in the X and Y direction), and Maximum (the number of counts at the peak of the star -- if it is 16383, the star is saturated and you need to use a shorter exposure time, or chose a fainter star). Write these in your focus table.

8) Increase the telescope focus by 1-2 units (to 2378-9 in our example) and hit Start Focus to take a new exposure at this focus setting. Carefully record the focus value and results associated with each image in your focus table -- it is easy to forget!

9) Repeat Step 8. If all goes well, you will see that the first exposures in your sequence had low, broad profiles and few counts at peak, but as the focus increased, the images got taller and narrower. At some point, the images began to broaden and flatten again. This means that you passed through best focus, and it is time to stop your sequence. Look back to decide which focus setting gave you the tallest, narrowest star shapes. This is your final focus value -- record it and the dome temperature on your observing log.

10) Set the telescope focus to the final value, but drive the focus 10-15 units below this value and approach it from below to avoid "backlash" effects.

11) Earlier, we zeropointed the telescope on a very bright star using the eyepiece. That center may not be right for the CCD, so we want to redo the telescope zeropoint using a fainter star with known RA/Dec. The focus stars will do nicely. This will ensure that the other objects you observe tonight will fall near the center of the CCD:

Updated 2002 Nov 12 -- ACL

Observing A Celestial Object

Note: The CCD is very sensitive to light -- pointing the CCD at the moon or a bright star or planet could result in permanent damage to the CCD. Never intentionally point the telescope at the moon or a bright planet (Venus, Mars, Jupiter, Saturn) while observing with the CCD! The instructions below describe a safe way of incrementally increasing your exposure time from short, safe exposures to the correct exposure time for your object.

In general, the longer the exposure time you can manage, the more detail will be visible in your picture -- up to a point. If the total number of counts in any pixel gets larger than 16,353 the computer can't handle it, and we say the object is "saturated". In many cases, an ideal exposure level is 12,000 counts for the brightest pixels in your object -- you want to adjust the exposure time to reach this level. Very faint objects like galaxies will probably never yield 12,000 counts, because the required exposure times are too long.

Note: Lately (Spring 2000), we have had trouble with the filter wheel occasionally sticking. If the filter wheel sticks, it will give you a dialog box saying something like "filter motion unsuccessful". If this happens, you will have to keep observing with whatever filter is present in the light path (this may impact your project). If it is before 11pm, call Andy and I will try to fix it.

1) Chose an object to observe and point the telescope to those coordinates.

2) In the "Maxim CCD" window, select the Expose tab. Do the following to take a test image with an exposure time of T_exp = 1 sec:

3) Inspect the test image:

4) For faint objects, you will probably need exposure times much longer than 100 sec. You will have to experiment to find what the longest practical exposure times are: probably 600 to 1000 sec. You can try to go longer, but I suspect (1) imperfect telescope tracking will result in blurred images, and/or (2) the background sky light will be very high (more than about 4,0000 counts). Faint objects like galaxies are fun and challenging ... play around and do the best you can!

5) Save all the images you want to keep by clicking the diskette icon (3rd button from the left on tool bar):

6) Record comments in your paper log such as Starname, UT/Local Time, Sidereal Time, CCD Temperature, Exposure/Filters, and especially Comments (eg, moon & sky conditions, problems, etc).

7) Different filters pass different amounts of light. If you change filters, you will probably have to redetermine the optimal exposure time. Start with short times and work your way up.

Updated 2002 Nov 12 -- ACL