In article . com,
jim wrote:
The background is that I've been trying out a Canon Powershot digital
camera on a tripod with the Canon Zoombrowser software that lets the
camera be controlled from a computer via the USB.

This works well but illuminating the subject (a ragbag of documents and
old pictures) with desk lights using ordinary GLS lights gives a
visible pulsing of light which can be seen in the monitor due to the
50Hz mains frequency. [which means 2 flashes per sec or 100Hz] This
isn't ideal as it clashes with typical camera exposure speeds.

I'd be surprised if what you're seeing is indeed the lights varying in
intensity. It's more likely to be something to do with the monitor.

--
*Never put off until tomorrow what you can avoid altogether *

Dave Plowman London SW
To e-mail, change noise into sound.