I was having a hard time trying to keep up with very mobile protozoans, one hand for the stage, one for the focus and trying to fire the camera with my nose. Charlie sent me this link http://www.peeters.com/300d.html which allowed me to make a foot switch. I've stuck a bit of velcro on the back so that it sticks to the carpet - works like a dream.
Kenv
Foot Switch
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