Pinch Zoom.. almost

Hey guys,

Does anybody have any idea of an algorithm that is similar to Apples pinch to zoom gesture? I am working on a resource for it, and I feel that I am really close, I just need to come up with a better algorithm. Currently my algorithm is really sensitive, if I move one of my fingers a few pixels it can zoom in/out all of the way.

Here's the algorithm that I have come up with:

void t2dPlaySceneWindow::pinchZoom()
{
    F32 currentPinchDistance = distance(mFirstFinger, mSecondFinger);
    F32 targetZoom = getCurrentCameraZoom();
   
    if(currentPinchDistance < mPreviousPinchDistance){
        // Zoom out
        F32 zoomLength = getCurrentCameraZoom() - mMinCameraZoomLimit;
        targetZoom -= 0.0005 * zoomLength * currentPinchDistance;      
    }else if(currentPinchDistance > mPreviousPinchDistance){
        // Zoom in
        F32 zoomLength = mMaxCameraZoomLimit - getCurrentCameraZoom();
        targetZoom += 0.0005 * zoomLength * currentPinchDistance;
    }
   
    if(targetZoom < mMinCameraZoomLimit)
        targetZoom = mMinCameraZoomLimit;
    else if(targetZoom > mMaxCameraZoomLimit)
        targetZoom = mMaxCameraZoomLimit;
   
    mPreviousPinchDistance = currentPinchDistance;
   
    setTargetCameraZoom(targetZoom);
    startCameraMove(0.0f);
}

The idea behind this algorithm is that the less space you have to zoom (zoomLength), the less a difference in the pinch difference makes. I probably could come up with an algorithm by hacking this one together and multiplying/adding different numbers to my current formulas, but I first wanted to see if the community had any elegant ideas.

Thanks,
Justin