Satellite Imaging with the LX200
August 8, 2000
Photographing artificial satellites at high magnification (150X) can be
challenging and rewarding.
(See photos: small [11K];
medium [24K];
large [24K].) Here are some tips that will help you.
A telescope with an electric motor drive is best for slewing in front
of a satellite. I use an 8-inch Meade LX200 that has electronic motor
control of positioning. I believe a Dobsonian telescope can be quickly
(manually) positioned in front of a satellite's track.
It's absolutely necessary to have your sighting scope perfectly aligned
with your video camera. Since the field of view (FOV) of your telescope,
at high mag, will be very small you must rely on looking through the
finder scope for positioning. I've found that the ratio of FOV is
something like 100 to 1. You MUST position so that the satellite passes
through the center of the crosshairs or you'll miss it on video.
A fast shutter speed is required to prevent blurring/streaking of final
images. If set for automatic the video camera will adjust the shutter to
the dark sky and be open too long. This will result in streaking of the
image. Unless you have a readout of the shutter speed setting, you'll
have to experiment to get a good setting. A coarse reference can be set
by looking at a star of known magnitude and adjust the shutter until the
star blinks-out.
NOTE: Faster shutter speed = less light! Small, faint
satellites will not produce useful images.
Focus
I focus on the Moon whenever possible. Otherwise focus carefully on a
bright star.
NOTE: Be very sure that your optics are aligned and clean.
Vibration
At high slewing rates vibration can be a problem. It also comes into play
when you're slewing over very short distances. While viewing through the
sighting scope, try to reposition so that the target is at the edge of the
FOV. Then try not to move the telescope until the target is past center.
It's sort of a leapfrog approach. With some practice you'll be able to get
at least 5 images to video during a satellite's transit. I've been able to
get as many as 12 passes during one satellite transit.
NOTE: Also be sure that all optics and mechanics are secured tightly.
I made a bracket that secures the eye-pc projection tube and video camera
to the main telescope tube.
Positioning
Even with a right-angle eyepiece adapter you'll find it uncomfortable
trying to follow a satellite above 70 degrees elevation. So, I simply don't
try. I catch the satellite as it's ascending and descending (~40-65 degrees).
It's moving slower then too (apparent motion).
Post Processing
I've gotten good results with a 2-head VCR and using a Snappy frame grabber.
Of course, a 4-head VCR is better (especially for still frame viewing).
Additionally, there are several pieces of hardware and software that can be
used to process the video images.
ADDITIONAL TECHNIQUES
An accurate timepiece is very helpful. Radio Shack sells a radio-clock that
picks up signals from an extremely accurate reference source. I also purchased
an audible countdown timer and wireless microphone from them.
When reviewing tapes it helpful to know what you're looking at. So I got a
video titler. I use it to display the target name, date, my location and
magnification directly in each video frame.
To create interesting videos in real-time I've hooked up a converted and manual
switch between my computer screen and the VCR. I can switch between info on the
computer screen and live video. This is very useful when using an astronomy
program such as Epoch2000 to control the telescope. A person viewing the tape
gets to see all the scope pointing parameters and then the telescopic image.
Ted Pittman, Tpittman@aol.com