|Image of Saturn Taken Near 2002
by: Rolf Meier
This picture of Saturn was taken within hours of opposition (opposite the sun) in 2002. According to Sky and Telescope magazine, the combination of wide open rings and nearness to perihelion make 2002 and 2003 "the finest for viewing Saturn in three decades". Notice features such as the Cassini division all around the rings, the shadow of the ball on the rings, and the Encke division.
Most of the equipment used for this picture was modest and low cost. Instead of an expensive CCD camera, a common webcam was used. Much of the software was free and available on the internet. The computer is several generations old. While the telescope is one of the more expensive components, it is not large by amateur standards and similar resolution is within grasp of most observers. The mechanical components driving the telescope and holding the camera to the telescope are home made.
There are many pictures of Saturn taken with a similar setup all over the Internet. Amateurs have discovered that inexpensive webcams offer a cheap way of imaging the planets. The trick is to remove the webcam's lens so that the image can be properly focused with an eyepiece or barlow lens. The next trick is to focus, and to keep the imaging element free of dust (luckily there is an optical window in front of the CCD).
Focusing is easier than with a conventional CCD because a webcam provides a "real time" view with instant feedback. Also, there are no color filters to change because the webcam's CCD has the color filters built in. Frames are downloaded at a fast rate, usually over a USB interface, at a maximum of 12 Mb/s. This can limit frame rates to just over 1 fps at the highest, uncompressed resolution. Even so, it is easy to generate hundreds of megabytes of data very quickly.
The real trick to getting a detailed picture is to combine images. This lessens the effect of random noise which appears in each individual image.
Some images of Saturn which appear on the internet are composed of thousands of individual frames. However, during the capture of so many frames the planet will have rotated and any features on the disc will have blurred. For Saturn this does not matter so much since it does not have so many spots, but rather bands with bland features. However, a planet such as Jupiter must be imaged within minutes because this planet contains a wealth of belt features. Any longer than 2 minutes or so and these spots will blur noticeably.
Here is a summary of the data for this picture:
date: December 17, 2002
time: 21:37 EST
seeing: very good
telescope: 6-inch f/12 Astro-Physics refractor
projection with 3X Televue Barlow lens to approx f/36
star diagonal used, therefore original images reversed
camera: 3Com HomeConnect PC Digital Webcam Lite (approx $100 but no longer available)
imaging element: 640x480 color CCD
webcam camera lens removed; no external IRB filter used
computer: 350 MHz Pentium II
image capture software: WinTLV time lapse shareware (approx $20)
camera settings: brightness 255, contrast 0, gamma 1, 640x480 RGB
capture rate: 750 msec to AVI file
total raw frames: 175 in about 2 minutes
selected good frames: 125, combined 25 at a time
AVI to BMP software: avi2bmp v0.49c (freeware)
BMP combining software: AstroStack (freeware)
first processing: unsharp masking PSF 6, LR deconvolution PSF 7 (Astrostack)
second processing: colour balance, contrast, and mirror with Paint Shop Pro
This page last modified: January 6, 2003