Canon DSLR cameras can not handle the trigger voltage of many of the after market flash units. The maximum trigger voltage that you can use is 6 volts. There are units that have trigger voltages of 200 volts and higher. You can burn up your camera if you use a flash with a trigger voltage over 6 volts. Here is a link to information on which flashes should be safe to use with your DSLR camera. I do know that my 1D can handle up to something like 250 volts. Iím not sure of the exact amount but I know that it is much more then the other Canon DSLR cameras. I would guess that the 1Ds is the same as the 1D. Please check this information before using a non-Canon flash unit on your Canon DSLR camera.
Canon Speedlite Flashes
Canon Flash Performance
Sigma Flash units
Thread on understanding EOS flash photography
Flash Photography with Canon EOS Cameras
Fill Flash Made Simple
Troubleshooting and Repair of Electronic Flash Units and Strobe Lights
Want to know the age of your equipment? Try this link.
When youíre ready to try some portrait photography a very good place to start is the Lighting Forum at DPreview. You will learn a lot about lighting and composition on that forum. The flash units that I bought were Alien Bees. These are powerful, light weight, and inexpensive units. They also have very fast recycle times.