My Astrophotography Equipment
b) CameraThe camera I use for planetary astrophotography is a Philips ToUcam Pro 740K. It's basically an upper-end computer webcam. Here's the details: Philips ToUcam Pro 740K Max resolution: 640 x 480 pixels (1280 x 960 for stills) Max frame rate: 60 fps Sensor: CCD This one is a very popular camera for astrophotography. However, Celestron and Meade have their own version as well. They are designed specifically for Astrophotography. See the "Further resources" section to the right.
Attaching the Webcam to the Telescope (Added June 2nd, 2008):Due to a number of requests, I added instructions for attaching the ToUcam to the telescope. Click on each photo below to view instructions.
Registax SoftwareThe 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. Registax download here.
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:
- Insert 2X Barlow lens. Webcam is not inserted yet.
- 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.
- 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.
- Center the planet and make sure it holds its position. A good polar alignment helps a lot here!
- Very carefully, switch to the webcam (i.e.., remove the eyepiece and insert webcam).
- 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
Center in Eyepiece AgainThis 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 for astrophotography, but became MUCH easier with practice!
FocusWhen 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:
Webcam AdjustmentsOnce 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:
Frame RateAnother 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:
Capturing the VideoI 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!
Registax ProcessingNext 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. 2/3/09 Update: Registax 4 tutorial here. Registax download here. 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). 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).
Further Processing- Adobe PhotoshopI won't spend too much time on this part. Please refer to the Photoshop Astrophotography Tutorial here for more information. Basically, the following tools in Photoshop are used to clean up the photo for the final version:
- Crop (to center image)
- Rotate canvas (for proper orientation)
- Levels (tonal range and color balance)
- Contrast Brightness Despeckle (cleans up some of the noise)
- Unsharp Mask (sharpens image but introduces noise!)
- Color Balance Hue & Saturation
Tips for Enhanced Planetary Imaging! Added June 2nd, 2008Be 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.