Thanks for the response
But i need to Ignore the Transformation for some items as they are required to retain the size independent of zoom level.

I didnt get your point, when you said "currently your implementation is incorrect as the scene doesn't see boundingRect() changes of your items, so it uses a too large boundingRect and redraws your items much too often".

Which item are you referring to ? The background item or the elliptical item?

I have also observing a strange behaviour,

When i set the update interval as 1msec, and run my app, the elllipse moves very fast but if i dont interact with the scene and leave the application alone, i dont see the movement of the item.
what could be the problem?