This creates the effect of looking through binoculars.

You can adjust the size, position and edge bleeding by changing the values for the Size X and Size Y (for a circle maintain a ratio of 1:1.79 for x:y), Position X and Position Y and the Transition width parameters respectively. In case you have clips on tracks below the clip where you apply this effect, the Alpha Operations effect makes sure that there is no alpha channel where other clips can be seen through. Otherwise you can delete it (keeping it doesn't hurt either).

After downloading move this to your Templates folder. If installed through Kdenlive you'll find the effect by simply searching for it or in the Templates folder in the Main Effects tab.