Webcam Astrophotography Tutorial for Planets

by Ray Shore

September 25th, 2005 (Updated April 29th, 2009)

1. Introduction

This webcam astrophotography tutorial is intended to explain my method for obtaining the planetary images found in my solar system image gallery. I hope it will be useful to those who are just starting out in astrophotography with a webcam. Below are a few of my favorite astrophotos that I have taken using my telescope and webcam. Click on thumbnails to view full size photo.

Incredible detail can be obtained with today's imaging techniques and software. I hope to demonstrate how this is done on a basic level in my webcam astrophotography instructions below. First though, I will start with the setup I use for astrophotography of planets.

4. Registax  Software

The method for obtaining high resolution images of the planets actually starts with a video taken with the webcam. The video is then processed in a freeware program called Registax  (by Cor Berrevoets) and results in a "stacked" image of several hundred frames. This will all be explained in detail later in this article. The Registax download can be found at: http://registax.astronomy.net.

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5. Finding the Planet Through the Webcam (webcam astrophotography method starts here)

The first step can be the most tricky part of it all! It is necessary to precisely center the planet in a relatively high power eyepiece. This must be done before switching to the webcam. Here are the steps involved:

1. Insert 2X Barlow lens. Webcam is not inserted yet.

2. Insert 32mm eyepiece for a low power, wide field of view. Adjust RA and DEC until the planet is as close to center as possible.

3. Carefully switch to the higher power eyepiece. I use a 10mm Plossl for this. This gives me about 400X magnification which is close to my highest "useful" magnification.

4. Center the planet and make sure it holds its position. A good polar alignment helps a lot here!

5. Very carefully, switch to the webcam (i.e.., remove the eyepiece and insert webcam).

6. Open the webcam software program. In my case, I use Spotlife which came with my Philips ToUcam Pro 740K. If the planet is not visible on the screen, it is usually due to 1 of 3 things: gain setting is too low, the planet is not centered (normally the case), or the telescope is WAY out of focus.

Gain Setting

One time I got frustrated because I could not get Saturn to show up on the screen. I was certain that it was centered well enough in the eyepiece. After quite a few minutes I decided to turn up the gain. Saturn was right there the whole time! So the best thing to try first is to turn up the gain. This is done in the webcam settings. I usually turn the gain up to about 75% to make the image bright enough to detect. 

Center in Eyepiece Again

This is normally the case. If the planet is still not visible, then follow the steps above again to center the planet. Normally it's just a matter of getting the planet centered in the webcam field of view. This was difficult when I first started using a webcam, but became MUCH easier with practice!

Focus

When all else fails, check the focus. It's possible (although unusual) for the image to be so far out of focus that it's too dim to detect. When the planet is in focus through my 10mm eyepiece, then it is usually visible (although not focused) through the webcam. I can easily make the adjustments once the planet is centered on the screen.  Here is a screenshot of what it looks like:

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6. Webcam Adjustments

Once the planet is centered on the screen, then it is time to make some adjustments to the webcam. First, I adjust the shutter speed and gain. To obtain the best quality, I normally select a shutter speed of 1/25 seconds or 1/33 seconds (or even 1/100 seconds in the case of Mars). I normally set the gain below 50%. It is important to keep the gain as low as possible but still see the detail. Otherwise, the finer details will be over-exposed. See screenshot below for typical settings:

Another important setting is the frame rate. The frame rate is directly related to image quality. Normally, I use a frame rate of 5 fps (frames per second) or 10 fps. Basically, 5 fps yields a higher resolution frame than 10 fps. However, by using 10 fps, I can obtain more frames (to stack) in a given time period. 5 fps works well when the seeing is very steady. Otherwise, I use 10 fps (which is most of the time!) Here's what the setting looks like:

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7. Capturing the Video

I normally take a 3-4 minute video (AVI) of the planets. This will yield hundreds of frames from which to stack (stacking process will be discussed later in the article). For example, if I take a 3 minute video at 10 fps, I will end up with 1800 frames (3 minutes x 60 seconds x10 fps). To a certain extent, the more frames available for stacking, the better the detail possible. It is important to note that there is a point where the detail will become blurred due to planet rotation. This is especially the case with Jupiter and its 10 hour rotation period. Thus, I limit my videos to about a 4 minute maximum recording time. As explained later, not all of the 1800 frames can be used during the stacking process.

Once I have started the video, I watch the planet to make sure that it does not drift off the screen. If it starts to get close to the edge, I make a fine adjustment to RA or DEC on the motor drive hand controller. The better I polar align my scope to start with though, the less I have to worry about drifting!

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8. Registax Processing

Next comes the fun part of processing the video. The program of choice for stacking frames is Registax. Since Registax 3 is the latest version of software as of this writing, I'll use it as an example. However, the basic principles are the same with any version of Registax.

Registax can be downloaded at http://registax.astronomy.net. Thanks to Cor Berrevoets (creator of Registax), it is available as freeware. His program is WELL appreciated!

Here is the basic procedure for converting an AVI video into a single stacked imaged.

1. Change screen area to 1024 by 768 pixels. In Registax 3, the entire screen is not visible with 800 by 600 resolution.
2. Open Registax and click on the select button at the top left of screen. Choose the video taken with webcam.
3. Scan the individual frames in the avi to find the best looking one. Frames will vary in quality from each other mostly due to the fluctuations in the atmosphere.  It is important to select a frame that provides the sharpest detail in the group since all others will be sorted according to this frame. Frames can be previewed by using the slider bar or the framelist. See screenshot below. Click to open in separate window (for easy reference).

4. Once the best frame is found, then an alignment box must be drawn around the image or particular feature within the image. I usually draw a box around the entire image though. There are several sizes of alignment boxes to choose from. These include 32, 64, 128, and 256. I select a size that is just large enough to completely surround the image of the planet.
5. Be sure to check the box "Use Colour".
6. In the Quality Estimate section, I select the Classic method and a Lowest Quality setting of 90%. This means that only those frames that are at least 90% as good as the reference frame will processed.
7. Click the Align button and the alignment process will begin.
8. At the end of the alignment process, note (at the bottom of screen) the stack size vs. the original number of frames. The lower quality frames (as compared to the reference frame) were screened out. Clicking the Limit button will eliminate the lower quality frames. Note the fewer number of frames for processing.
9. Now click on the Stack tab. Further refinement will be performed here. If the Stackgraph is not already displayed, click on the tab. Note the 2 sliders. The vertical slider is for difference cutoff. This is adjusted downward to eliminate those frames that are significantly different from the others. Here I cut off any large spikes. The horizontal slider controls the quality of the frames. The graph slopes downward from left to right. The left side being the highest quality frames (again, as compared to the originally selected reference frame) and the right side being the least quality frames. Better frames are selected as the slider is moved to the left. As this adjustment is made, the number of frames shown at the bottom of the screen will change.
10. When the best frames are selected, it is time to stack them together. Registax combines all the selected frames (that were at least 90% as good as the reference frame plus the additional manual adjustments) into a final composite image. I like to have a stack of at least 300 frames. The more frames that are stacked, the better the signal to noise ratio (more signal, less noise). Since each frame varies a bit in the amount of detail that was captured, the final stack will be a nice composite with lots of detail!
11. Now click the Wavelet tab. This is where the magic begins! Click the contrast tab and move the slider slightly to the left for both contrast and brightness. Note the wavelet sliders in the screenshot below.

12. Now it is time to adjust the wavelet sliders to bring out the detail in the composite image. I normally only adjust the sliders for layers 2-5. A lot of trial and error takes place at this stage. As the sliders are moved to the right, detail is brought out of the image. A nice balance must be struck between under-processing and over-processing the photo. If the wavelets aren't adjusted enough, then not all of the available detail will be brought out in the image. Over adjusting however will only make the photo grainy (noise). Here is a screenshot of the image above after some adjustment of the layers:

As you can see, the detail really stands out! Now it is time to polish up the image for final version.

13. Click on the Final tab. Click on the Save Image button or copy it to the clipboard. Note that final processing can be performed here. However, I prefer to finish it up in a photo editing program (Adobe Photoshop normally).

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9. Further Processing- Adobe Photoshop

I won't spend too much time on this part. Basically, the following tools in Photoshop are used to clean up the photo for the final version:

10. Final Image!

11. Tips for Enhanced Planetary Imaging! Added June 2nd, 2008

• Be sure that you have precise collimation of your telescope. This is especially critical for high power planetary imaging.
• Image during very good seeing conditions. You'll want to image when there is a stable air mass above you. Check the sky clock if there is one available for your area at: http://www.cleardarksky.com.
• Set your scope up outside at least 1 hour before imaging. If it hasn't had time to reach thermal equilibrium with the outdoor temperature, then the image can become distorted due to tube currents.
• Tweak the focus until you get the sharpest image possible "overall". The planet will appear to go in and out of focus constantly. This is due to an unstable atmosphere that you are imaging through. Spend a lot of time getting the best possible focus you can.

12. Tools of the Trade

If you're interested in webcam astrophotography of the planets, here are some resources to get started.