Hi, I'm trying to produce an effect as though a magnifying glass is magnifying an image. I hoped to do it by making a copy of the portion the magnifying glass lies over, enlarging it and cropping away the excess.

Here's a screenshot, to give you a better idea:

The wells of circles are grouped and the magnifying glass is a group.

How do I trim away the excess?

Is the path that draws up the edge of the glass complete elipse? If yes, try duplicate it.
Then select the elipse AND the background image.
Click: Object -> Clip -> Set

Perfect! Thanks very much

When I group them, the old stuff reappears - is it possible to stop that from happening?

seans_potato_biz wrote:Perfect! Thanks very much

When I group them, the old stuff reappears - is it possible to stop that from happening?

Avoid group objects that belong to different layers. It doesn't work properly in Inkscape. There reason is something about thechnical spesification of svg format - I don't remember the rest of the story.