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Meade Pictor XT-Series CCD Autoguider/Imagers
 Section 12: CCD Tutorial
IMPORTANT NOTICE! Never use a telescope or spotting scope to look at the Sun! Observing the Sun, even for the shortest fraction of a second, will cause irreversible damage to your eye as well as physical damage to the telescope or spotting scope itself.

Introduction

This section will discuss the principles behind CCD technology, its advantages and disadvantages, and the things needed to take good quality images. This is not meant as a comprehensive CCD reference, but rather a quick introduction to the basics for the beginning imager.

If you are new to CCD imaging...

This section is written for those who are either new to astronomical imaging or would consider themselves "casual" CCD imagers.

If you consider yourself to be accomplished or expert, you can skip this section and go to Section 2.

This section will guide you through each step necessary to get an image using the Pictor CCD Imaging System and your telescope.

Before you try to image actual celestial objects, you should practice setting up your telescope with the Pictor and your PC and make some daytime images. In this way, you will become very familiar with the basic operation of the camera and the software. Familiarity with your equipment and consistency in working with your system are necessary to get good images you will be proud of. For your convenience, two daytime exposure setups are provided.

Now, let's get set up...

Making Your First Image; a Daytime Shot



1. Properly set up your telescope as described in your telescope user's manual.

2. If you have a large aperture telescope, you will need to make a cardboard cover for the objective lens with a 0.5" - 1" diameter hole halfway between the center and the rim. This limits the amount of light falling on the CCD chip and is necessary for daylight images.

3. Focus the telescope for use with the camera. Focusing a telescope with a CCD camera attached is one of the most difficult tasks in CCD imaging. Once a rough focus is attained, the focus may be easily fine tuned using the Focus Mode, described in step 10 of this section. The following step details how to obtain the first approximate focus. Your telescope should be pointed at a large, relatively bright object that is not too close (200feet or more if possible).

4. Take the focusing ring and slide it over the guiding barrel. You will need to unscrew the black back of the barrel, then slide the ring on, and reattach the black back. Slide the focusing knob until it is against the black end of the barrel (the end that screws on to the Pictor). Now tighten the ring by using the thumbscrew.

Next, attach a piece of scotch tape to the open end of the imaging barrel where the Pictor would attach. Insert the barrel into the eyepiece holder of your telescope as far as it will go (it should stop against the focusing ring), and lock the barrel in place. With your eye about 1 foot back from the tape, you will see a projection of the image on the scotch tape. Turn the focuser until this image is sharply focused. Remove the tape and imaging barrel. Take the focusing ring off the guiding barrel and reassemble the barrel. You may see page A6 of the Appendix and make a parfocal eyepiece at this point. You should have an approximately focused telescope. You will need to repeat this procedure at night the first time, since the focus will change when moving from a relatively near terrestrial object to a celestial object such as the Moon.

5. Connect and turn on the Pictor and your PC as described in Section 1of the Users' Manual.

6. Start the PictorView XT software. Select Set User Preferences from the File Menu. Select the COMM port the camera is connected to. For most users, this will be COM1 or COM2. Also select the baud rate. If you have Windows95,this can be up to 56K, for Windows 3.1 you must start in standard mode to connect at any baud rate above 19.2K. If you have Windows for Workgroups3.11, you cannot select anything above 19.2K unless you have a custom high speed serial driver (i.e. from Digi or RocketPort). If you are not sure, select 19.2K. Select OK. Note that this only needs to be done the first time you run PictorView XT.

7. Click the X button on the far right of the toolbar. After a couple of seconds, the right of the status bar at the bottom of the screen should read "On Com 1 @ 19.2k" where 1 is the comm port and 19.2kis the baud rate. You are now ready to take an image. If you receive an error message, check the cable connections and make sure you have selected the correct COMM port in Step 6. You may need to switch to COM2, for example.

8. Now select the Exposure dropdown box in the center of the toolbar. There will be a listing of predefined exposure setups to select. Select the one called Daytime1. Now click the camera icon on the toolbar. You will see a message "Taking Exposure", then another message "Preparingimage for download, please wait". This may appear for a few seconds. Then a percent box will appear showing the download status. The percentages may not increase smoothly and may hang for several seconds; this is normal. The total download time will be 1min - 2min at the most. If you get a message saying "Communication Error; Retry, Cancel", with Retry and Cancel buttons, press Retry. If the message reappears without any increase in download status, press Cancel. Note: this message can be caused by interference from electrical appliances, or poor serial connections.

9. You should now have an image on your screen. If the image is out of focus, you may try the Focus Mode. This is entered by clicking on the Focus icon on the toolbar (it looks like a target). Focus mode will download an image, then ask you to draw a box around a subframe. This is so that a part of the image (the part you want to focus on) is downloaded each time, for quicker response. Draw the subframe by holding down the left mouse button and moving the mouse to from a rectangle around the object you want to focus on. When you release the left button, a dialog will appear asking if this subframe is OK. After clicking YES (you can click no and redraw another subframe),a window will appear that has two rectangles in it. After a few seconds, an image will appear in the left window (the image should match the subframe you drew).

Every few seconds, the image will update, and the previous image will be moved to the right window. This is so that you can see if the focus is getting better or worse. To focus, wait until the image appears, the move the focus knob on your telescope. Wait for one or two updates of the focusing window, and you will see if the focus is getting better or worse. It is important to not move the focusing knob too much at each turn, or you may go past focus. This will depend on how sensitive the focuser is on your telescope. When the image is focused, press the Done button. The focusing window will disappear within a few seconds (it may be in the middle of downloading, which can take a few seconds). If the object is too far away or the day is hot or windy, perfect focus may not be obtainable due to atmospheric conditions.

If you have a Meade LX200 with an electric focuser, you will not need to manually focus the telescope as long as you have set up your LX200 options in Set User Preferences under the File Menu and you have a second serial port on your PC to connect to the RS-232 port on the LX200.

10. You now have a focused Pictor. When repeating this step at night, you can make a small mark on the focusing tube of your telescope if you wish; this will enable you to come closer to focus before entering the Focus Mode. Alternatively, you can adjust the position of the ring on your parfocal eyepiece.

11. Now select the Exposure Setups dropdown list and select Daytime binned. Click the Camera icon. You will notice the download time is much quicker. When the image appears, it is one quarter the size of a full image. This is a process called binning, which has several advantage:

1. Downloads are much faster.

2. The image is sharper.

3. The signal to noise ratio is improved.


Any of the Exposure Setups may be binned by selecting them from the list box, then pressing the Edit Setup tool (on the toolbar to the right of the Setups list box). Then click Binning On, then Save. That Exposure Setup will now produce a binned image. Note that you cannot change the name of the Default setup. For more information, see Edit Setups under the Camera Menu.

12. Experiment with other options in the Edit Setups window; Number of frames, Prescale, Antiblooming, Gain, and Shift and Combine. The number of frames option will take multiple images without any further intervention, for example, type 3 in the entry field, then click Save. Now, anytime you select that Exposure Setup and click the Camera icon, the camera will take 3 identical images. Up to 50 shots can be taken this way.

Prescale is important for night shots, which most of your images will be. This option will automatically set the background and range of the image to display your shot in the best possible manner without processing. To further adjust the background and range, use the arrow keys on the keyboard.(Background and range is analogous to brightness and contrast). The antiblooming feature is also most useful for night time shots. This will help prevent a bright star from blooming, or saturating part of the image.

Gain is the amount of amplification applied to the camera signal. A setting of 1 is acceptable for most images, but faint nebula may need a setting of 2. Settings higher than 2 should rarely be used. Presets are provided for all these options which will cover most situations. For more information on other options such as Automatic New Dark Frame, and Flat Field, see the Camera Menu section.

The Shift and Combine feature allows the camera to take several exposures and add them together to produce a single image. This is desirable because the Pictor cannot effectively expose for more than 25 minutes or so, but some faint objects can benefit from long exposures. Also, many telescopes cannot track an object accurately for more than a few minutes without being manually guided or attached to an autoguider. Finally, note that all Pictor cameras can autoguide as well as image.

Shutting Down the Camera

To end your imaging session, disconnect from the Pictor by pressing the X button on the toolbar. You can select Perform Safe Shutdown to ensure that your Pictor does not warm up too abruptly, which can cause hot pixels to appear. Hot pixels are pixels that will always read brightly no matter what you are imaging. If you forget to do a controlled shutdown once in a while don't worry; it takes many times for the hot pixel problem to show up.

The First Nighttime Image

1. After getting familiar with the software, you are now ready to begin night imaging. For the first session, it is probably best to pick a target such as the Moon. Set up the telescope and camera as you did for daytime imaging. Remember to repeat Steps 4 and 5 to refocus your telescope and readjust your parfocal eyepiece. Select one of the Lunar Exposure Setups from the dropdown list, then connect to the camera by pressing the X icon. Click the Camera icon. You should now have a picture of the Moon! If the image is too dim or bright, try varying the background and range using the arrow keys. If it is still not correct, you may need to change the exposure time in the Exposure Setup.

2. To save an image, press F2. A default path and suggested file name will appear. You can change the file name and format by retyping them in the area provided.

3. Continue imaging the Moon or planets if you wish, or you can move onto deep sky imaging.

4. Deep Sky imaging: this is taking images of objects such as nebulae, double stars, clusters, and galaxies. For good deep sky images, good calibration frames are essential. See the section following this introduction and the section on Imaging With the PictorView Software in Section 2 of the User's Manual (or the Viewing Images section) for detailed information about calibration frames. Exposure times for deep sky objects will vary widely depending on the objects magnitude, seeing conditions, telescope size, etc. A sampling of DeepSky setups are preset for your convenience, but you will surely want to fine tune them as you gain experience.

Customizing and Adding Exposure Setups

As you gain experience, you will want to create custom Exposure Setups or change the options on the presets. PictorView XT allows you to do this easily. There are a total of 16 possible Exposure Setups, including the Default. Ten of these are predefined when you receive your camera, the other 6 are called User1 to User6. To create a custom setup, select one of the user setups in the dropdown list on the toolbar, then click the Edit Setup icon. Make the changes you want in the Edit Setup window and give the setup a name, such as MyDeepSky or Binned Moon, or whatever is meaningful to you. Click Save, and the new setup appears in the dropdown list. The same procedure can be applied to renaming or modifying the preset Setups. There is a special setup, called Default, that is always loaded. This setup may be modified just like any other, but its name cannot be changed. Use this to enter your most common options. Also, on the Edit Setup window there is a button called Shoot Now. This button allows you to take an exposure immediately. This is the same as clicking Save, then clicking the Camera icon.

CCD Technology

A CCD (Charge Coupled Device) is a semiconductor device similar to the integrated circuits found in televisions and computers. It's usually a small (less than 1" square) silicon chip subdivided into as many as 4 million picture elements, commonly known as pixels.

The pixels are arranged in a matrix, or rectangle. The figure below displays a simplified arrangement of pixels on a chip, with an individual pixel highlighted.

When light (in the form of a photon) hits a particular pixel, an electron is generated. The CCD chip will store this electron at the location of the pixel; for example, if a photon of light hits a pixel at the upper right of the CCD chip, the electron will be stored at the upper right of the CCD chip. More than one electron can be stored at a particular pixel location; if a number of photons hit a specific pixel, a corresponding number of electrons will be stored at that location.

By tracking the number of electrons stored at a particular location on the CCD chip, the Pictor can monitor any changes (movement of stars) in its field of view. For example, if a large number of photons have hit one pixel, this probably indicates the location of a particular celestial object. As these electrons move across the CCD chip, the Pictor 208 is alerted to that object's movement in the sky. Then the Pictor can send the commands to the telescope to keep it centered on that object.

Likewise, the Pictor can transmit the pixel data to the PictorView XT software which takes the intensities (the number of electrons that have struck each pixel), and converts that into a useable, visible picture.

Imaging Fundamentals

The most important things in CCD imaging are calibration, consistency, cooling, and patience. Calibration is taking sets of calibration frames (discussed in the next topic), and consistency means being consistent in everything; a steady temperature that is as cool as possible (cooling), taking calibration frames at the same temperature as the image frames, always remembering to log everything, always following a checklist (see sample in appendix).

Patience is needed because sometimes it can take several tries to make an excellent image.

A final tip is do not delete any raw frames. Images that look terrible can look excellent after being cleaned up. Images always look worst right out of the camera.

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