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Two of the most popular webcams for planetary imaging are the Philips ToUCam Pro and the Celestron NexImage.  Both include easy-to-use control software.  Philips calls their software VRecord and Celestron uses Microsoft's AMCap.  Both are basically identical in operation, so this tutorial covers either camera.  Fancier programs like K3CCDTools also work well for capturing images.  While the specific steps outlined here may not work exactly with other programs, the basic ideas still apply.


Basics of Webcam Imaging

The idea behind webcam imaging is to capture a video file of a planet (or the moon or sun).  The video is usually taken at a rate of 10 to 30 frames per second.  In this way, a single 60-90 second video file contains 600 to 1800 individual frames.  Processing software such as Registax can then reject the blurry frames and stack the sharp frames to create a final image with incredible detail.


Initial Settings

Begin by making sure Preview is checked under the Options menu.  This will display the current image on the screen.

Select Options > Video Capture Pin to change the default image size.  In the Output Size pulldown menu at the bottom of the window, select 640x480.  This will allow you to capture the largest possible image with the camera.

Above:  Setting the Output Size to 640x480

I recommend starting with the camera exposure set to Full Auto.  The planet will be overexposed, but will be easier to locate initially.  Manual settings may underexpose an out-of-focus planet and make it impossible to see.


Finding & Focusing

With the preview mode enabled, you can now center and focus the object.

Tip:  Center the target in a high-power eyepiece before attaching the webcam to the scope.  This will increase the likelihood of the object being in the field of view.

Frame the object as desired using the telescope's fine adjustment controls.  Unless your telescope is perfectly polar aligned (which is not necessary for planetary imaging), you may notice the object slowly drifting out of the field of view.  You might find it best to place the object on one side of the field so that it drifts across the field (rather than out of it) during the duration of the video capture.

Focusing for planetary imaging can be a tad tricky, but with a little practice it can be easy to tell when the telescope is precisely focused.  Since webcam imaging is done at high magnification, the telescope make shake slight when the focus knob is touched.  A motorized focuser can be handy for webcam imaging but is by no means essential.  The planetary images on this website (in this tutorial and the Registax tutorial, for example) were all manually focused.  However, a fine focuser such as the Feathertouch Focuser by Starlight Instruments is recommend (and was used for the images on this site).

Allow the image to settle down for a moment after touching the focus knob.  Watch the image for a few moments as atmospheric turbulence will come and go causing the image to blur then sharpen over a few seconds, even when you are not touching the scope.

Look for a distinct detail such as the Cassini Division in Saturn's rings or the ice caps on Mars.  These features may only be visible in the live preview image when the focus is ideal.

Note:  The live preview image will bear little resemblance to the final processed file.  So don't expect stunning detail in the preview.  After spending a little time with the webcam you will learn when the conditions are best.  When you can see reasonably impressive detail in the preview image, you will know the final image should be great.

Above:  A single frame from a raw video of Jupiter compared to the final image obtained from the same video.  The image on the left would be considered a pretty good raw preview image, so if you get an image like this, you are doing well.


Exposure Settings

To change the exposure settings, go to Options > Video Capture Filter.  This will open the Camera Properties window.  Begin by unchecking the Full Auto checkbox under Control.

Tip:  For imaging the moon, you can leave Auto checked and the exposure settings need not be changed.

Above:  Initial exposure settings in the Camera Controls window, with Full Auto control disabled

Above:  Auto exposure disabled so gain and shutter speed can be set manually.  Auto White Balance usually does a good job and does not need to be manually set.

Drag the Camera Controls window to one side so you can see the live image in the preview window.  There are three main categories you will use to adjust the exposure: Image Controls, Exposure, and Frame Rate.  The other settings are typically not used for astronomical imaging.  The three categories are listed below in the order in which you set them, not the order they are listed in the window.

Frame Rate (Image Controls tab)

This is the first control to set.  It is recommended to use 10 frames per second (fps) or slower.  At faster frame rates, the camera needs to compress the image data to cram it through the USB cable fast enough.  This leads to image artifacts.  10 fps avoids any image compression.

Note:  You must also set the frame rate in the Set Frame Rate window under the Capture menu as described below.

Exposure (Camera Control tab)

Increasing the Gain control increases the exposure but it also boosts noise.  It is best to leave the Gain control as low as possible and set the correct exposure using the other sliders.  For a fainter target, or when using a smaller or slower scope, the Gain may need to be increased, but in general, leave it as low as possible.  (As an example, try leaving the cover on the webcam and increase the gain to its highest setting.  You will see a fairly bright image despite the fact that no light is reaching the webcam chip.  This is all gain noise.)

The Shutter Speed can be set to change the exposure time.  Note that the shutter speed cannot exceed the frame rate, so 1/10 second is the longest possible exposure for 10 fps.  For bright planets and the moon, decreasing the Shutter Speed is normally necessary.  If one exposure setting is too bright and the next shorter Shutter Speed too dim, use the Brightness control described below to fine tune the image brightness.  A common misconception concerning webcam imaging is that faster frame rates are better for stopping the seeing conditions.  Faster frame rates compress the data, so a slower rate is preferable.  The length of the exposure is controlled by the shutter speed, not the frame rate.  This means you can set a shutter speed of, say, 1/75 second whether the frame rate is 10 fps or 30 fps.

Image Controls

There are three sliders that can be adjusted in this category.  (Note that Contrast is disabled in manual exposure mode.)  Brightness can be used to fine tune the brightness of the image after setting the Shutter Speed as described above.  It is best to get the best exposure setting possible with the Shutter Speed control first, then adjust the Brightness if necessary. 

Gamma essentially controls the contrast of the image.  Moving the slider to the right brightens the image and moving it left darkens the image.  Once the other settings have been made you can fine tune the look of the image with the Gamma slider.

It is a good idea to add some Saturation to the video image.  While saturation can be increased in Photoshop, etc., it is best to get a good color rendition from the outset.  However, you don't want to overdo it either, especially since you will be able to make adjustments later.  Boosting the Saturation a little but not too much is recommended.


Capture Settings

Two other controls must be set before starting the video capture.  Under the Capture menu, select Set Frame Rate.  If this setting does not match the frame rate selected in the Camera Controls window, the wrong frame rate will be used.  Set this to the same frame rate selected above and make sure Use Frame Rate is checked.

Above:  Frame rate set to 10 fps

Select Capture > Set Time Limit.  This is where you will tell the software how long you want the video clip to be.  60 to 180 seconds is typical.  This will capture 600 to 1800 frames at 10 fps.  Be sure Use Time Limit is checked.

Above:  Time limit set to 120 seconds

Choosing a Video Capture Length

So, how long a video clip should you take?  It depends primarily on the total number of frames you want to capture.  If you are imaging at 10 fps and you want 1000 total frames, you need to take a video clip 1000/10 = 100 seconds long.  So the real question then becomes, how many total frames do you want?  If you decide that you want to keep the best, say, 40% of your images, and you want to stack 400 images to create the final image, you will need 1000 total frames (since 40% of 1000 is 400).  If you want to use the best 30% of the frames, and you want to stack 500 frames for the final image, you will need 1667 total frames (since 30% of 1667 is 500).  See the Registax tutorial for more details on deciding how many total frames to use.

Above:  Comparison of 100 frames (left) and 500 frames (right).  Note the significant decrease in noise in the right image.


Setting Capture File

The last step is to set the capture file.  Select File > Set Capture File.  Select the folder where you would like to save the file (or create a new folder if necessary) and type in an appropriate file name.  You may wish to include the date or telescope used in the file name for future reference.

Above:  Setting the file name for an image of Mars


Capturing the Video File

Select Capture > Start Capture and click OK in the window that appears to begin capturing the video file.

Above:  Ready to Capture window confirming the video sequence name and directory

The camera will begin taking the video sequence.  At the bottom of the screen it will display the number of frames captured, time elapsed and any frames dropped (there may be a few dropped but not many).

Above:  Video clip of Mars with final statistics displayed

Once finished you can select a new file name under Set Capture File and take another image or close the camera control software to begin processing the video file in Registax or similar program.

Note:  If you do not select a new file name, the previous file will be overwritten.

See the Registax tutorial for tips on processing a video file.

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