I have used setInterval now instead of onEnterFrame. I think movement is smoother and it seems to be ok.
http://www.barkerfamily.plus.com/
the code is:
// set up the function. Because the setInterval is running more quickly than
// the frame rate I have to include an updateAfterEvent
function follow (clip1,clip2) {
clip1._x =
clip2._x;
clip1._y =
clip2._y;
updateAfterEvent();
}
// call the function and pass it the arguments
setInterval(follow,1,binoculars_mc,mask_mc);
// set up the mask layer
vista_mc.setMask(mask_mc);
(the fla is very simple but if anyone wants it I will post it).