I have an MP with 0.72 viewfinder. I am planning to buy a Summicron 28 mm lens. Do I need the 21/24/28 mm accessory Viewfinder? When I review the description of the product, it seems to indicate that I may not need it, unless the lens is below 28 mm, or, if you have a 0.85 viewfinder, in which case you WOULD need the accessory Viewfinder. "The basic design of the viewfinder mechanism of the Leica M limits the image field view in such a way that bright line frames for focal lengths below 28 mm cannot be included in any of the viewfinder configurations. In the case of the 0.85X viewfinder the bright line frame for the 28 mm focal length is also no longer possible to include." Can anyone shed any light on this.