Zoom between images on a Canvas

Question

Hi,

I have a background bitmap drawn to the Canvas with drawBitmap(), I then have a secondary image drawn on top of this, smaller and with transparent sections.

Just working with this canvas: http://developer.android.com/reference/android/graphics/Canvas.html

I need to make the transparent sections of the second image essentially like a magnifying glass. So the transparent sections of the second image need to zoom in on the background image underneath by a configurable factor. So effectively im moving a magnifying glass over the background image, and need to do the zoom effect.

Anyone have any ideas how to do this? I've seen it done in opengl by altering the FOV, but I really just want to work with the canvas here if possible, as OpenGL ES seems horrendous to learn for a simple 2d game...

Thanks for any help